Self healing polymer compositions

Abstract

There is provided a polymer composition comprising a first polymer phase and a second polymer phase, wherein: a) the first polymer phase comprises a thermoplastic polymer matrix modified with an adhesive functional group or a group which is a precursor of an adhesive functional group; and b) the second polymer phase comprises a thermoplastic polymer capable of acting as a self-healing agent and being chemically reactive on healing of the polymer composition.

Claims

1. A polymer composition comprising a first polymer phase and a second polymer phase, wherein: a. the first polymer phase comprises a thermoplastic polymer matrix modified with an adhesive functional group or a group which is a precursor of an adhesive functional group, wherein said adhesive functional group or said group which is a precursor of an adhesive functional group comprises a polar functional group; and b. the second polymer phase comprises a thermoplastic polymer that is provided in the thermoplastic polymer matrix as a dispersion of discrete portions, that is capable of acting as a self-healing agent and being chemically reactive to form a volatile by-product on healing of the polymer composition, wherein said thermoplastic polymer comprises one or more functional groups selected from the group consisting of amine, acid, hydroxyl, epoxy, ketone, ether, ester, and salts thereof.

2. The polymer composition according to claim 1, wherein the ratio of the thermoplastic polymer of the second polymer phase to the thermoplastic polymer matrix of the first polymer phase is in the range of 4:1 to 1:4, or is 1:1; or wherein the thermoplastic polymer matrix of the first polymer phase comprises a non-polar polymer, or a polyolefin; or wherein the polyolefin is selected from the group consisting of polyethylene and polypropylene.

3. The polymer composition according to claim 1, wherein the thermoplastic polymer matrix of the first polymer phase comprises: a graft copolymer of polyethylene and a monomer selected from the group consisting of maleic anhydride, maleic acid, and mixtures thereof; or a graft copolymer of polypropylene and a monomer selected from the group consisting of maleic anhydride, maleic acid, and mixtures thereof.

4. The polymer composition according to claim 1, wherein the thermoplastic polymer matrix of the first polymer phase further comprises a partially neutralized polymer.

5. The polymer composition according to claim 1, wherein the thermoplastic polymer of the second polymer phase comprises an ester, wherein the thermoplastic polymer of the second polymer phase is a functionalized polyolefin or copolymer thereof; or wherein the functionalized polyolefin or copolymer thereof is a functionalized polyethylene or copolymer thereof; or wherein the functionalized polyethylene or copolymer thereof is polyethylene co-methacrylic acid (EMAA).

6. The polymer composition according to claim 1, wherein the thermoplastic polymer of the second polymer phase is not encapsulated in an encapsulating agent.

7. The polymer composition according to claim 1, further comprising one or more additives, wherein the additive is selected from the group consisting of pimelic acid, citric acid, and mixtures thereof.

8. A coating comprising the polymer composition according to claim 1, wherein the coating comprises a third polymer phase, wherein the third polymer phase comprises a thermoset polymer matrix or one or more polymerizable thermoset agents capable, on curing, of producing the thermoset polymer, wherein optionally the thermoset polymer comprises an epoxy, wherein optionally the thermoset polymer matrix comprises an epoxy based resin, or the one or more polymerizable thermoset agents comprise epoxy resin forming agents, and wherein the epoxy resin forming agents comprise a resin and a hardener.

9. The coating according to claim 8, wherein the thermoplastic polymer of the second polymer phase is provided in the form of one or more layers in between the first polymer phase of the polymer composition and the third polymer phase, wherein optionally each of the one or more layers of the thermoplastic polymer of the second polymer phase has thickness of 150 to 500 m.

10. The coating according to claim 8, further comprising a fourth polymer phase, wherein the fourth polymer phase comprises a polymer material that is compatible with the first polymer phase of the polymer composition, wherein optionally the fourth polymer phase polymer material is a non-polar polymer material, wherein optionally the fourth polymer phase polymer material is polyolefin, wherein optionally the polyolefin is selected from the group consisting of polyethylene, polypropylene, polybutylene, and mixtures thereof.

11. The coating according to claim 10, wherein the thermoplastic polymer of the second polymer phase of the polymer composition is provided in the form of one or more layers in between the first polymer phase of the polymer composition and the fourth polymer phase, wherein optionally each of the one or more layers of the thermoplastic polymer of the second polymer phase has thickness of 150 to 500 m.

12. A method for preparing the polymer composition according to claim 1, comprising the steps of: a) modifying a thermoplastic polymer with an adhesive functional group or a group which is a precursor of an adhesive functional group, wherein said adhesive functional group or said group which is a precursor of an adhesive functional group comprises a polar functional group, to form the thermoplastic polymer matrix of the first polymer phase; and b) adding to the first polymer phase, a thermoplastic polymer capable of acting as a self-healing agent and being chemically reactive to form a volatile by-product on healing of the polymer composition to form the second polymer phase, wherein said thermoplastic polymer comprises one or more functional groups selected from the group consisting of amine, acid, hydroxyl, epoxy, ketone, ether, ester, and salts thereof.

13. The method according to claim 12, wherein the modification of the thermoplastic polymer in step (a) is conducted at a temperature of at least 140 C., wherein optionally the modification of the thermoplastic polymer in step (a) comprises mixing the thermoplastic polymer with a component providing the adhesive functional group or the group which is a precursor of an adhesive functional group at a speed of at least 160 rpm, wherein optionally the modification of the thermoplastic polymer in step (a) is conducted under solvent-free conditions, wherein the modification of the thermoplastic polymer in step (a) comprises chemically reacting the thermoplastic polymer with the adhesive functional group or the group which is a precursor of an adhesive functional group.

14. The method according to claim 12, wherein prior to step (a), said thermoplastic polymer is mixed with said component providing the adhesive functional group or said group which is a precursor of an adhesive functional group.

15. The method according to claim 12 further comprising step (c) heating said thermoplastic polymer matrix of the first polymer phase and said second polymer phase to form a melt, wherein optionally the method further comprises step (d) cooling said melt to disperse said second polymer phase in said thermoplastic polymer matrix of the first polymer phase.

16. A method of self-healing cracks that form in a coating according to claim 12, comprising the step of applying a stimulus to the coating to cause the thermoplastic polymer of the second polymer phase to at least partially fill said crack, and removing said stimulus to allow the thermoplastic polymer of the second polymer phase to bond the edges of said crack together.

17. The method according to claim 16 wherein the stimulus is selected from the group consisting of heat, pressure, and combinations thereof; or wherein optionally the heat is applied at a temperature of at least 90 C., or wherein the heat is applied at a temperature that is less than the melting point of the first polymer phase, the third polymer phase, and/or the fourth polymer phase, or wherein optionally the temperature is about 120 C.

18. The polymer composition according to claim 1, wherein said discrete portions are in the form of particles having a diameter that is sufficient to provide a reservoir of said thermoplastic polymer of the second polymer phase for self-healing to occur, wherein said diameter is at least 5 m.

19. The method according to claim 12, wherein step a) further comprises adding a free radical initiator, wherein the free radical initiator is selected from the group consisting of 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane (BBTCH), 1,1-di(tert-butylperoxy)cyclohexane (BBCH), dicumyl peroxide (DCP), ,-di(tert-butylperoxy)diisopropylbenzene (DIPB), di-tert-butyl peroxide (DBP), 2,5-di(tert-butylperoxy)-2,5-dimethylhexane (DTBH), di(tert-butylperoxy)-2,5-dimethylhexyne (DTBHY), tert-butyl-hydroperoxide (TBHP), cumyl hydroperoxide (CHP), tert-butyl peroxy benzoate (TBPB), 2-phenylazo-2,4-dimethyl-4-methoxypentanenitrile, dibenzoyl peroxide, lauroyl peroxide, and mixtures thereof; or wherein step a) further comprises adding a co-agent, wherein the co-agent is selected from the group consisting of stearamide, styrene, methacrylamide and caprolactam.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The accompanying drawings illustrate a disclosed embodiment and serves to explain the principles of the disclosed embodiment. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

(2) FIG. 1 shows the screw design of the extruder used for the laboratory scale processes.

(3) FIG. 2a shows the adhesive failure of the unmodified ETILINAS LL0209AA LLDPE polymer.

(4) FIG. 2b shows the cohesive failure of the MAH-modified ETILINAS LL0209AA LLDPE polymer.

(5) FIG. 3 shows a chart comparing the peel strength of a commercially available adhesive formulation against that of the ETILINAS LL0209AA LLDPE reactively modified with MAH and various concentrations of initiators (0.5 wt %, 1.0 wt %, and 3.5 wt %).

(6) FIG. 4 shows a three dimensional chart of the effect of barrel temperatures (average) and screw speeds on grafting efficiency of MAH onto ETILINAS LL0209AA LLDPE using two different initiators (di-benzoyl peroxide and lauroyl peroxide).

(7) FIG. 5 shows FTIR spectra of samples of adhesive compositions obtained from grafting LLDPE with MAH using various amounts (0 wt %, 1 wt %, 2 wt %, 3 wt % and 4 wt %) of the initiator di-benzoyl peroxide (Luperox A75).

(8) FIG. 6 shows the adhesive strength of various MAH-grafted LLDPE samples wherein various processing and fabrication conditions were varied. The sequence of numbers on the x-axis refers to: Extrusion temperature ( C.): fabrication temperature ( C.): fabrication time window (sec): Fabrication time (min) in the same order.

(9) FIG. 7 shows the adhesive strength of the unmodified LLDPE, MAH-grafted LLDPE, and LLDPE grafted with MAH and a partially neutralized polymer (5 wt % Surlyn 9970 or 5 wt % Nucrel 2940), with addition of 2 wt % initiator (Luperox A75 or Lauroyl Peroxide) with an extrusion temperature of 230 C., a fabrication temperature of 200 C., a fabrication time window of 30 sec, and a fabrication time of 6 min.

(10) FIG. 8a shows the failure surface of the MAH-grafted LLDPE peel test coupon obtained using scanning electron microscopy (SEM).

(11) FIG. 8b shows the failure surface of the Nucrel-modified grafted LLDPE peel test coupon obtained using SEM.

(12) FIG. 9 shows the FTIR spectrum of the unmodified Y022 polypropylene against the FTIR spectra of three Y022 polypropylene samples grafted with MAH, prepared by varying the amount (wt %) of the dicumyl peroxide (DCP) initiator, the MAH (maleic anhydride), stearamide (SA), and increasing the screw speed (thereby reducing the residence time).

(13) FIG. 10 shows the FTIR spectrum of the unmodified Y022 polypropylene against the FTIR spectra of Y022 polypropylene samples grafted with MAH, prepared by varying the amount (wt %) of the dicumyl peroxide (DCP) initiator, the MAH (maleic anhydride) and stearamide (SA), and reducing the screw speed (thereby increasing the residence time).

(14) FIG. 11 shows the FTIR spectrum of the unmodified Y022 polypropylene against the FTIR spectra of Y022 polypropylene samples grafted with MAH, prepared by varying the amount (wt %) of the dicumyl peroxide (DCP) initiator, the MAH (maleic anhydride) and stearamide (SA).

(15) FIG. 12 shows a chart comparing the MFI values of the polypropylene adhesive samples. The samples that displayed adhesive properties are annotated on the chart. std refers to unmodified polypropylene. std thru extruder refers to unmodified polypropylene put through the extruder without modification. The remaining samples were prepared by varying the amount (wt %) of the dicumyl peroxide (DCP) initiator, the MAH (maleic anhydride) and stearamide (SA), and varying the rate of addition of additives.

(16) FIG. 13 shows the screw design of the extruder used for the industrial scale production of the polyethylene and polypropylene adhesives.

(17) FIG. 14 shows the FTIR spectra of the polyethylene pre-trial product samples.

(18) FIG. 15 shows the FTIR spectra of the polyethylene product samples taken at various time periods during processing (1 hr, 4 hr and 8 hr on day 1, 1 hr and 8 hr on day 2).

(19) FIG. 16 shows a chart comparing the grafting efficiency of the unmodified polyethylene against those of the modified samples taken at various time periods during processing.

(20) FIG. 17 shows the MFI values of the polyethylene samples collected during processing.

(21) FIG. 18 shows the adhesion strength results for various polyethylene product samples.

(22) FIG. 19 shows the FTIR spectra obtained for comparative grafting sample (101008S5), comparative adhesive sample, pre-trial 100 kg batch, the production sample 5, the production sample 7, and Y022 polypropylene.

(23) FIG. 20 shows the FTIR spectra obtained for all of the polypropylene production samples 1 to 7.

(24) FIG. 21 shows the adhesion test results obtained for all of the polypropylene production samples 1 to 7.

(25) FIG. 22a shows the load versus extension data for the sample of Nucrel 2940 blended with the 5 wt % Nucrel-modified maleic anhydride grafted in a 2:1 ratio.

(26) FIG. 22b shows the load versus extension data for the sample of Nucrel 2940 blended with the 5 wt % Nucrel-modified maleic anhydride grafted in a 1:1 ratio.

(27) FIG. 22c shows the load versus extension data for the sample of Nucrel 2940 blended with the 5 wt % Nucrel-modified maleic anhydride grafted in a 1:2 ratio.

(28) FIG. 23 shows the healing efficiency for various formulations with varying ratios of Nucrel 2940 (healing agent) to modified adhesive from 2:1 to 1:9, and without addition of Nucrel 2940, under conditions of elevated temperature (High Temperature) or pressure (Extra Load).

(29) FIG. 24 shows the Differential Scanning calorimetry (DSC) thermograms for the formulations with varying ratios of Nucrel 2940 (healing agent) to modified polyethylene adhesive from 2:1 to 1:9, and without addition of Nucrel 2940.

(30) FIG. 25 shows the DSC thermogram displaying the glass transition temperature for the formulations with varying ratios of Nucrel 2940 (healing agent) to modified polyethylene adhesive from 2:1 to 1:9, and without addition of Nucrel 2940.

(31) FIG. 26a shows a SEM image of the fractured surface of a modified adhesive wherein the ratio of healing agent:modified grafted LLDPE is 1:9.

(32) FIG. 26b shows a SEM image of the fractured surface of the modified adhesive wherein the ratio of healing agent:modified grafted LLDPE is 1:4.

(33) FIG. 26c shows a SEM image of the fractured surface of the modified adhesive wherein the ratio of healing agent:modified grafted LLDPE is 1:2.

(34) FIG. 26d shows a SEM image of the fractured surface of the modified adhesive wherein the ratio of healing agent:modified grafted LLDPE is 1:1.

(35) FIG. 26e shows a SEM image of the fractured surface of the modified adhesive wherein the ratio of healing agent:modified grafted LLDPE is 2:1.

(36) FIG. 27 shows a schematic representation of the pressure delivery mechanism.

(37) FIG. 28a shows the optical microscopic surface of the 10 wt % citric acid modified adhesive formulation after healing.

(38) FIG. 28b shows the optical microscopic surface of the 10 wt % pimelic acid modified adhesive formulation after healing.

(39) FIG. 28c shows the optical microscopic surface of the unmodified adhesive formulation after healing.

(40) FIG. 29a shows the load versus extension data for the unmodified adhesive, and 2 wt % and 10 wt % pimelic acid modified adhesive formulation before and after healing.

(41) FIG. 29b shows the load versus extension data for the unmodified adhesive, and 2 wt % and 10 wt % citric acid modified adhesive formulation before and after healing.

(42) FIG. 30a shows the optical image illustrating cohesive failure of the unmodified adhesive formulation.

(43) FIG. 30b shows the optical image illustrating cohesive failure of the 2 wt % citric acid modified adhesive formulation.

(44) FIG. 30c shows the optical image illustrating cohesive failure of the 2 wt % pimelic acid modified adhesive formulation.

(45) FIG. 31a shows the load versus extension data of samples before and after healing for formulations containing varying concentrations of the Nucrel 2940 (healing agent) from 10 wt % to 67 wt %.

(46) FIG. 31b shows the peak load data for samples before and after healing for formulations containing varying concentrations of the Nucrel 2940 (healing agent) from 10 wt % to 67 wt %.

(47) FIG. 32a shows the load versus extension data of samples before and after healing for formulations containing varying concentrations of the Nucrel 2940 (healing agent) from 8 wt % to 50 wt %, and 2 wt % of pimelic acid.

(48) FIG. 32b shows the peak load data for samples before and after healing for formulations containing varying concentrations of the Nucrel 2940 (healing agent) from 8 wt % to 50 wt %, and 2 wt % of pimelic acid.

(49) FIG. 33a shows the load versus extension data of samples before and after healing for formulations containing varying concentrations of the Nucrel 2940 (healing agent) from 18 wt % to 50 wt %, and 2 wt % of citric acid.

(50) FIG. 33b shows the peak load for samples before and after healing for formulations containing varying concentrations of the Nucrel 2940 (healing agent) from 18 wt % to 50 wt %, and 2 wt % of citric acid.

(51) FIG. 34 shows the optical and SEM images of the 2 wt % citric acid and 2 wt % pimelic acid modified adhesive formulation containing 38 wt % of Nucrel 2940.

(52) FIG. 35a shows an optical image of the primer surface of the 2 wt % pimelic acid modified adhesive formulation exhibiting the bubbles responsible for the pressure delivery healing mechanism.

(53) FIG. 35b shows a SEM image of the 2 wt % pimelic acid modified adhesive formulation containing 18 wt % of Nucrel 2940 showing evidence for the adhesion of phase separated particles after healing.

(54) FIG. 35c shows an optical image of the 2 wt % pimelic acid modified adhesive formulation containing 18 wt % of Nucrel 2940 illustrating cohesive failure after healing where some adhesive were found adhering to the under side of the topcoat.

(55) FIG. 36a shows an optical image of the primer surface of the 2 wt % citric acid modified adhesive formulation exhibiting the bubbles responsible for the pressure delivery healing mechanism.

(56) FIG. 36b shows a SEM image of the 2 wt % citric acid modified adhesive formulation containing 18 wt % of Nucrel 2940 showing evidence for the adhesion of phase separated particles after healing.

(57) FIG. 36c shows an optical image of the 2 wt % citric acid modified adhesive formulation containing 18 wt % of Nucrel 2940 illustrating cohesive failure after healing where some adhesive were found adhering to the under side of the topcoat.

(58) FIG. 37a shows the DSC analysis of the pimelic acid modified adhesive formulation showing the consistency of the glass transitional point.

(59) FIG. 37b shows the DSC analysis of the citric acid modified adhesive formulation showing the consistency of the glass transitional point.

(60) FIG. 38 shows the load versus extension data of the adhesive formulation modified with varying ratios of Nucrel 2940/EVA from 50/10 to 0/50.

(61) FIG. 39 shows a chart on the peak load data for the adhesive formulation modified with varying ratios of Nucrel 2940/EVA from 50/10 to 0/50.

(62) FIG. 40 shows the optical and SEM image of 50:0 EVA:Nucrel 2940 modified adhesive showing the phase separation and bubbles on the polymer surface.

EXAMPLES

(63) Non-limiting examples of the invention, including the best mode, and a comparative example will be further described in greater detail by reference to specific Examples, which should not be construed as in any way limiting the scope of the invention.

Example 1

Standard Protocols

(64) (a) Preparation of Adhesive Coupons

(65) Three layer coatings were prepared by powder coating fusion bonded epoxy (FEE) (Scotchkote FBE Coating 226N+8G from 3M) to a steel substrate, and then applying an adhesive and topcoat. The surface of the steel (AS/NZS 3678-250 XLERPLATE) was first wiped with methyl ethyl ketone (MEK) and sandblasted. The sample coupons were cut to pieces having dimensions of 120 mm30 mm3 mm, powder coated with the FBE to a thickness of about 80-100 m, placed on a Teflon coated hotplate, and allowed to equilibrate at the desired temperature of 190 C. to 230 C. when a polyethylene based adhesive sample was used, and 160 C. to 200 C. when a polypropylene based adhesive sample was used. A pre-cut adhesive layer and topcoat layer were placed on the sample and a 2.15 kg roller was applied to the sample evenly at least three times. The sample was removed from the hot plate after 2 minutes and used for peel testing. Where a polyethylene based adhesive sample was used, the topcoat used was Etilinas PC4012 (Petronas), and where a polypropylene based adhesive sample was used, the topcoat used was PETRONAS Y022.

(66) (b) Peel TestEvaluation of Adhesive Performance

(67) Peel testing was performed according to the standard DIN 30670 protocol for testing of polyethylene coatings for steel pipes and fittings (April 1991), or the standard DIN 30678 protocol for testing of polypropylene coatings for steel pipes (October 1992) using a jig set up on an adhesion testing machine (Instron 5566). The sample was placed on the jig and locked into position using adjustable metal supports and locking pins. A cord connecting the base of the jig to the cross-head beam assists the base of the jig to move at the speed of the cross-head to keep the peel angle consistent. As the cross-head beam moves, the adhesive is peeled away from the metal at about 90.

(68) (c) Fourier Transform Infrared (FTIR)Quantification of Level of Grafting

(69) Fourier Transform Infrared (FTIR) spectroscopy was used for semi-quantitative measurement of the level of grafting that resulted from modification of the polyolefin. The FTIR was performed using a Thermo Nicolet 5700 FTIR or a Bruker Equinox, followed with analysis of the spectra using the OMNIC Version 7.1 software.

(70) A calibration curve was first constructed using commercially available MAH-grafted polyethylene (Sigma Aldrich) containing 0.4 wt %, 0.5 wt % or 0.85 wt % grafted MAH. The calibration curve was then used for comparison of the level of grafting between the samples prepared as well as against commercially available benchmarks.

(71) Samples were prepared for analysis by dissolving 3 g of the polymer via refluxing with xylene for 3 hrs, followed by precipitation with acetone, drying in an oven at 100 C. for 1 hr, and pressing into a film of about 0.1 to 0.3 mm thick using a hydraulic press set at 230 C.

(72) (d) Melt Flow Index (MFI)

(73) The melt flow index (MFI) of the samples was determined using the ISO 1133 protocol. The polymer sample was pushed through a die at 190 C. using a 2.16 kg weight. The amount of sample collected after 10 min was taken to be the MFI value (g/10 min).

(74) (e) Floating Roller Test Fixture

(75) The floating roller test was conducted using the ASTM D3167 protocol.

(76) (f) Differential Scanning Calorimetry (DSC)

(77) A TA Instruments DSC-2920 (Delaware, USA) was used to determine the melting points and miscibility of the samples. A sample (5 mg) was placed in an aluminum crucible and heated from 30 C. to 220 C. at a rate of 10 C./min under nitrogen. The melting points and miscibility of the samples were then determined from the DSC spectra.

(78) (g) Scanning Electron Microscopy

(79) Scanning electron microscopy was conducted using a Leica 440 scanning electron microscope at a voltage of 20 kV.

Example 2

Solvent-Based Reactive Modification of Polyethylene (PE)

(80) (a) Extrusion Screw Design

(81) The design of the extrusion screw used in the grafting process was found to be important for optimizing the mixing time and the level of chemistry taking place between the polymer reactants of a sample in the reaction zone, and minimizing degradation of the polymer reactants. As shown in FIG. 1, the screw (1) used was a Haake 25 mm Twin Screw (L/D 36) designed to comprise two mixing zones (2, 3) interspersed between conveyance regions (4, 5, 6). Each mixing zone in the screw used is made up of regions to facilitate forward, neutral and reverse mixing directions. In this way, the level of mixing between the polymer reactants was maximized, which maximized reaction between the polymer reactants, prior to the extraction zone (7).

(82) (b) Sample Preparation

(83) Various samples comprising the polyethylene PETRONAS Etilinas LL0209AA (LLDPE), maleic anhydride (MAH) (Sigma Aldrich) (as grafting agent), methyl ethyl ketone (MEK) (as solvent) (Sigma Aldrich) and tert-butyl peroxybenzoate (TBPB) (as free radical initiator) (LuperoxP from Sigma Aldrich) were prepared according to Table 1 below.

(84) TABLE-US-00001 TABLE 1 Sample compositions for modification of polyethylene with MAH in solvent-based system Sample TBPB (wt %) MAH (wt %) LLDPE in MEK (wt %.) 1 0 0 100 2 0 50 50 3 0.5 50 49.5 4 1 50 49 5 2 50 48 6 3.5 50 46.5
(c) Modification Process

(85) The above reactants were fed into the mixing zone (2), FIG. 1, of the extruder to allow the chemical reaction to proceed. The temperature was monitored throughout the process, and was observed to be relatively consistent, varying between 190 C. and 220 C. across the barrel of the extruder.

(86) (d) Results

(87) FIG. 2 compares the adhesion performance of an unmodified ETILINAS LL0209AA (LLDPE) polyethylene coupon with that of a modified ETILINAS LL0209AA (LLDPE) polyethylene coupon prepared as set out above in Table 1. FIG. 2a shows a clean smooth surface of an unmodified ETILINAS LL0209AA (LLDPE) polyethylene coupon while FIG. 2b shows cohesive failure of the modified ETILINAS LL0209AA (LLDPE) polyethylene coupon, as evidenced by the presence of LLDPE particles still remaining on the HDPE.

(88) FIG. 3 shows the peel test results for the samples 1 (unmodified), 3 (with 0.5 wt % initiator), 4 (with 1.0 wt % initiator) and 6 (with 3.5 wt % initiator) of Table 1 against the commercial benchmark, Fusabond EMB 100D. The MAH-modified samples 3, 4 and 6 displayed excellent adhesive properties that were comparable to (sample 6) or higher (samples 3 and 4) than that of the commercial benchmark. Hence, when 0.5 wt % or 1.0 wt % of initiator was used in combination with the optimal level of MAH, the polyethylene exhibited significantly higher adhesive strength than the commercial benchmark. In particular, when 1.0 wt % of the free radical initiator was added to the formulation, the peel strength increased significantly to more than 90 N/cm, which was double that of the commercial benchmark. In contrast, the unmodified polyethylene sample (sample 1) did not exhibit any adhesive properties.

Example 3

Solvent-Free Reactive Modification of Polyethylene (PE)

(89) (a) Reactant Feeding

(90) For solid phase (solvent-free) modification of polyethylene, an initiator/MAH mixture was fed into the barrel of the extruder comprising the screw of FIG. 1 at the same point as the ETILINAS LL0209AA (LLDPE) polyethylene through a parallel port using a micro-twin screw feeder. In the feeding process, the micro-twin screw feeder ground the initiator/MAH mixture together such that they had similar particle sizes and were well dispersed and mixed. This differs from the solvent-based modification in Example 2 above, where the initiator/MAH mixture was dispensed directly into the mixing zone of the extruder barrel.

(91) (b) Optimization of Screw Speed and Barrel Temperature to Improve Grafting Efficiency

(92) 1.83 wt % MAH, 98.1 wt % LLDPE and 0.037 wt % of initiator (either di-benzoyl peroxide (Luperox 75A) or lauroyl peroxide) were fed into the extruder at 50 g/hr. The reaction was conducted at varying screw speeds from 120 to 340 rpm, and at varying barrel temperatures from 120 C. to 240 C. The readings collated were computed into a three-dimensional plot as shown in FIG. 4.

(93) FIG. 4 shows the impact of varying the barrel temperature and screw speed of the extruder on the efficiency of grafting. It can be seen that increasing the temperature and screw speed led to an increase in the level of grafting. To achieve at least about 36% of grafting efficiency, a barrel temperature of about 140 C. and a screw speed of at least 240 rpm were applied when lauroyl peroxide was used as initiator. When the temperature applied was 180 C., the screw speed was 240 rpm, and di-benzoyl peroxide (Luperox 75A) was used as initiator, the grafting efficiency was about 39%.

(94) FIG. 4 also compares the effectiveness of two different initiators, di-benzoyl peroxide (Luperox 75A) and lauroyl peroxide, under the reaction conditions studied. It can be seen that di-benzoyl peroxide is a more efficient initiator at promoting grafting of MAH onto the polyethylene LLDPE under the reaction conditions studied.

(95) FIG. 5 shows the FTIR spectrum obtained for the LLDPE grafted with MAH in the presence of varying amounts of the initiator di-benzoyl peroxide from 1 wt % to 4 wt %. The carbonyl peak attributed to MAH at about 1700 cm.sup.1 in the FTIR spectrum is clearly evident in all of the samples. It can also be seen from the FTIR spectrum that increasing the initiator concentration resulted in higher levels of grafting as reflected by the higher peak at 1700 cm.sup.1.

(96) (c) Adhesion Strength of Samples

(97) FIG. 6 shows the adhesion strength of different MAH-grafted LLDPE samples obtained by varying reactant and/or reaction conditions of the extrusion process. The numbers on the x-axis of the chart represent the following parameters from left to right: extrusion temperature ( C.), fabrication temperature ( C.), fabrication time window (sec), and fabrication time (min).

(98) The samples that were prepared at extrusion temperatures of 230 C., fabrication temperatures of 200 C., fabrication time windows of 30 sec and fabrication time of 4-6 min resulted in adhesive performance that was significantly higher than the adhesive performance of a commercial standard and the DIN 30670 target of 35 N/cm.

(99) (d) Addition of Partially Neutralized Polymers

(100) A further study on improving and controlling the adhesive properties of the ETILINAS LL0209AA polyethylene polymer was conducted by adding additives to the MAH-grafted ETILINAS LL0209AA polyethylene polymer in a second extrusion step. The additives tested were the ionomer Surlyn 9970 and Nucrel 2940.

(101) The samples were prepared as follows: a) 2 wt % Luperox was fed from one micro-hopper (or feeder) and combined with ETILINAS LL0209AA polyethylene fed from another hopper at the same time. b) 2 wt % Lauroyl Peroxide was fed from one micro-hopper (or feeder) and combined with ETILINAS LL0209AA polyethylene fed from another hopper at the same time. c) 2 wt Luperox and MAH were fed from one micro-hopper (or feeder) and combined with ETILINAS LL0209AA polyethylene fed from another hopper at the same time. d) 2 wt % Lauroyl Peroxide and MAH were fed from one micro-hopper (or feeder) and combined with ETILINAS LL0209AA polyethylene fed from another hopper at the same time. e) 2 wt % Luperox and MAH were fed from one micro-hopper (or feeder) and combined with ETILINAS LL0209AA polyethylene fed from another hopper at the same time. 5 wt % Surlyn was added in a second extrusion run through a separate single screw extruder. f) 2 wt Lauroyl Peroxide and MAH were fed from one micro-hopper (or feeder) and combined with ETILINAS LL0209AA polyethylene fed from another hopper at the same time. 5 wt % Surlyn was added in a second extrusion run through a separate single screw extruder. g) 2 wt % Luperox and MAH were fed from one micro-hopper (or feeder) and combined with ETILINAS LL0209AA polyethylene fed from another hopper at the same time. 5 wt % Nucrel 2940 was added in a second extrusion run through a separate single screw extruder. h) 2 wt % Lauroyl Peroxide and MAH were fed from one micro-hopper (or feeder) and combined with ETILINAS LL0209AA polyethylene fed from another hopper at the same time. 5 wt % Nucrel 2940 was added in a second extrusion run through a separate single screw extruder.

(102) As shown in FIG. 7 the addition of 5 wt % of either the ionomer (Surlyn 9970) or the ethylene methacrylic acid copolymer (Nucrel 2940) resulted in a substantial increase in adhesive performance that surpassed that of the commercial standard and the target DIN 30670 standard.

(103) FIG. 8 shows two examples of the failure surface obtained using scanning electron microscopy (SEM). FIG. 8a shows the SEM of a MAH-grafted LLDPE and FIG. 8b shows the SEM of a Nucrel-modified MAH-grafted LLDPE. Both samples exhibited cohesive adhesive failure and therefore, good adhesive performance.

Example 4

Solvent-Free Reactive Modification of Polypropylene (PP)

(104) (a) Optimization of Feed Composition and Screw Speed to Improve Grafting Efficiency

(105) A range of formulations were prepared by varying the amounts (wt %) of dicumyl peroxide (DCP) initiator, the MAH (maleic anhydride), stearamide (SA), and increasing or decreasing the screw speed (thereby reducing or increasing the residence time, respectively). The FTIR spectra of the resultant formulations were subsequently evaluated and are shown in FIGS. 9, 10 and 11, while the MFI values are shown in FIG. 12.

(106) To compare the results semi-quantitatively, the FTIR spectra in FIGS. 9 to 11 were normalized using the peak at about 1150 cm.sup.1 as reference. This peak was selected because it is considered to be part of the polymer backbone and therefore not expected to undergo any changes. Once normalized, the spectra were offset so that the baselines of the carbonyl peaks were consistent with each other.

(107) As can be seen from FIG. 9, when the amounts of the DCP, MAH and SA were doubled and the residence time was kept constant, the peak around the 1800 cm.sup.1 wavelength region showed significantly higher absorbance. This suggests that a higher percentage of MAH was bonded successfully to the YO22 polypropylene polymer, which in turn leads to better adhesive strength. In contrast, when the screw speed was increased (which resulted in a reduction of the residence time and thus the available reaction time), no observable changes in the grafting efficiency was seen when the concentrations of the reactants were doubled. In fact, for the sample with higher concentrations of reactants, reduced residence time resulted in a reduction in the size of the peak.

(108) As shown in FIG. 10, reducing the initiator and co-agent concentrations led to a reduction in the size of the peak at about 1800 cm.sup.1. Accordingly, reducing the wt % of these two parameters leads to a decrease in grafting efficiency.

(109) As shown in FIG. 11, further reducing the initiator and MAH concentrations while increasing the concentration of the stearamide co-agent resulted in comparatively poor levels of grafting as reflected by the small peak sizes.

(110) (b) Peel Test

(111) Quantitative peel tests results could not be obtained for the polypropylene adhesives samples because when positive adhesive qualities were present, the brittleness of the topcoat led to cracking and/or splintering of the top coat before adhesive cohesive failure could occur. Hence, the peel test could only be qualitative in nature. The samples which resulted in positive adhesive qualities are as indicated in FIG. 12.

(112) (c) MFI Data

(113) FIG. 12 also shows the MFI values of the different polypropylene adhesive samples prepared by varying the amounts (wt %) of dicumyl peroxide (DCP) initiator, the MAH (maleic anhydride), stearamide (SA), and the rate of addition of additives. The MFI was seen to vary from sample to sample and is indicative of the level of degradation/chain scission that occurred during processing. The samples with MFIs higher than the commercial benchmark (Borealis BB108E) all also displayed adhesive properties. It can also be seen that two formulations were developedone with a high MFI of the order of 20 (that is, good grafting was achieved but higher levels of degradation occurred), and one with a lower MFI of the order of 12 (that is, good grafting was also achieved but lower levels of degradation occurred) that is comparable to the commercial benchmark. As can also be seen from FIG. 12 (std thru extruder), simply mixing and processing the unmodified polypropylene at elevated temperature without any modification also resulted in some level of degradation. Hence, some degree of degradation is inevitable during modification.

Example 5

Scale-Up Production of Polyethylene Adhesive

(114) (a) Sample Preparation

(115) Two 200 kg batches (pre-trial samples) of MAH-grafted polyethylene adhesive were prepared, both with and without the antioxidant package of chemicals that are typically used, according to the compositions as shown in Table 2 below.

(116) Each 200 kg batch was prepared by blending multiple batches in a 25 kg capacity speed mixer for 1 min at low speed (55 rpm), 1 min at high speed (90 rpm) and 1 min again at low speed (50 rpm).

(117) To prepare a two tonne batch of MAH-grafted polyethylene adhesive based on Formulation 2 in Table 2, a different method of mixing was used, hereinafter referred to as the manual bag transfer mixing method (MBTM). The additives were first mixed in the 25 kg capacity speed mixer with an equal quantity of polyethylene powder for three minutes. The mixture was then added to polyethylene powder in a bulk storage bag for a total mass of 500 kg. To allow further mixing, the polymer blend was transferred from bag to bag by pouring from a height of about 1 m to mix the components. During the transfer to the bag underneath, further mixing was achieved through manual intervention using a shovel. This process was repeated four times before mixing was considered complete.

(118) TABLE-US-00002 TABLE 2 Compositions of samples in scale-up production of polyethylene adhesive Formulation 1 Formulation 2 Components Mass (Kg) (%) Mass (Kg) (%) ETILINAS LL0209AA 24.51 97.71 24.47 97.56 (powder) Maleic anhydride 0.457 1.82 0.457 1.82 Luperox 75A (di benzoyl 0.0093 0.037 0.0093 0.037 peroxide) Calcium stearate 0.025 0.10 0.025 0.10 Phosphite(Irgafos 168) 0.025 0.10 Phenolic(Irganox 1010) 0.013 0.05
(b) Reactive Modification

(119) Reactive modification was performed using a Coperion twin screw ZSK50MC (L/D40) reactive extruder. The screw design is shown in FIG. 13. As with the screw used in the laboratory scale experiment (shown in FIG. 1), the screw (8) in FIG. 13 also has two mixing zones (9, 10) interspersed between conveyance regions (11, 12, 13). Each mixing zone in the screw used is made up of regions to facilitate forward, neutral and reverse mixing directions. In this way, the level of mixing between the polymer reactants was optimized, which optimized reaction between the polymer reactants.

(120) The extrusion conditions for both pre-trial and trial production formulations were as follows: Torque: 81% Output rate: 150 kg/hour Pressure: 46 bar Melt temperature: 239 C. Screw speed: 280 rpm Heat zones: 180, 185, 190, 195, 200, 205, 210, 215, 220, 230 C.
(c) FTIR Analysis

(121) The FTIR spectra of the pre-trial samples prepared above are shown in FIG. 14. It can be seen that good grafting was achieved as evidenced by the strong carbonyl stretching peak derived from the MAH at 1780 cm.sup.1. The presence of anti-oxidants not only did not interfere with the level of grafting, but increased the level of grafting slightly.

(122) The anti-oxidant based formulation was scaled up to prepare 1.9 tonnes of polyethylene adhesive (trial samples). Samples were collected throughout the extrusion process and the FTIR spectra on the samples are shown in FIG. 15. Like the pre-trial systems, the level of grafting appears very good with all trial samples exhibiting very strong MAH carbonyl stretching peaks at about 1780 cm.sup.1. This was confirmed by comparison with virgin unmodified polymer (with no grafting). The grafting was consistent throughout the extrusion process as can be seen in FIG. 16.

(123) (d) MFI Analysis

(124) Analysis of the MFI of each sample was performed to monitor the extent of polymer degradation during processing. The results are shown in FIG. 17, which show chemical reactive modification having occurred in the extruder barrel. The MFI value of a virgin polymer (unmodified) was MFI of 0.94 while the MFI values of the grafted adhesive samples ranged from about 0.20 to about 0.50.

(125) (e) Adhesion Performance

(126) The adhesion strength between the primer layer and the topcoat layer is an important measure of adhesive performance. The results of peel tests on the production trial samples are shown in FIG. 18. All samples displayed good adhesive performance and are typically well above the required DIN 30670 industry standard. Two tests were useda primary test using a floating roller test fixture and a re-test using the peel test.

Example 6

Scale-Up Production of Polypropylene Adhesive

(127) (a) Sample Preparation and Reactive Modification

(128) A 100 kg pre-trial batch based on the polypropylene formulation shown in Table 3 below was prepared using the same manual method as previously described above for the preparation of the polyethylene adhesive in Example 5.

(129) TABLE-US-00003 TABLE 3 Compositions of samples in scale-up production of polypropylene adhesive Component Mass (kg) (%) YO22 489.35 97.87 Dicumyl peroxide 0.6 1.2 Maleic anhydride 4.4 0.88 Stearamide 4.4 0.88 Calcium stearate 0.5 1.0 Phosphite (Irgagos 168) 0.5 1.0 Phenolic (Irganox 1010) 0.25 0.05

(130) The following processing conditions were used for reactive modification of the pre-trial batch: Heating zones: 180, 185, 190, 195, 200, 200, 210, 210, 210, 215 C. Melt Temperature: 209 C. Screw speed: 320 rpm Torque: 77% Melt pressure: 29 Bar Output: 250 kg/hr

(131) A 1 tonne batch of the same formulation was prepared via 2500 kg batches and was prepared according to the MBTM method as described above. The extrusion conditions used at the beginning of the production run were: Heating zones: 155, 155, 160, 160, 160, 160, 160, 175, 210 C. Melt Temperature: 174 C. Screw speed: 160 rpm Torque: 65% Melt pressure: 11 Bar Output: 110 kg/hr

(132) Under the above conditions, good processing of the polypropylene was observed, which occurred rapidly at about 200 kg/hr.

(133) (b) MFI Analysis

(134) A sample of the polypropylene adhesive at the end of the pre-trial was taken for MFI measurement and FTIR analysis. During the production run, several samples were taken at different stages of the process and at different processing conditions, and the MFI measured. Table 4 below shows the number of samples collected during production of the polypropylene adhesive showing the time the sample was collected, the MFI and the key extrusion parameters changed during the production run.

(135) TABLE-US-00004 TABLE 4 Samples collected during production of polypropylene adhesive showing the times at which the samples were collected, the MFI values and the key processing parameters changed Collection Key extrusion MFI Sample Time (hr) condition changed (g/10 min) Pre-trial 1 19.6 Production 1 * 37.61 sample 1 Production 3 (no change) 24.53 sample 2 Screw speed = 160 rpm Production 3.5 (no change) 31.67 sample 3 Screw speed = 160 rpm Production 4 Output - 170 kg.hr; 22.39 sample 4 Screw speed = 200 rpm; Melt temp. = 179 C. Production 4.5 Output = 200 kg/hr; 22.05 sample 5 Screw speed = 235 rpm Production 1 hr Output = 200 kg/hr; 31.37 sample 6 (day 2) Screw speed = 235 rpm Production 1.5 hr Output = 200 kg/hr; 23.48 sample 7 (day 2) Screw speed = 235 rpm * Sample was dried in an oven beforehand at 100 C. and may have affected the run. A second sample was collected after 2 hrs using the sample extrusion conditions and the MFI was 24.53.

(136) The MFI of the pre-trial sample was 19.6, compared to 2.9 for the unmodified YO22 polypropylene formulation. The increase in MFI indicates some polymer degradation is inevitable when the polypropylene undergoes grafting.

(137) (c) FTIR Analysis

(138) The samples for FTIR analysis were taken from the pre-trial 100 kg batch, the trial production run 5, and the trial production run 7. The data is shown in FIG. 19, which compares these samples to two comparative samples exhibiting good grafting and good adhesion propertiescomparative grafting sample (101008S5) and comparative adhesive sample. Grafting was seen to have occurred for all samples, as evidenced by the presence of MAH peaks at about 1780 cm.sup.1. In all cases, the polypropylene adhesive samples were normalized against an internal standard peak at 1260 cm.sup.1 and then offset for clarity if necessary. The peaks from the production trial samples are also similar in size to the two comparative samples exhibiting good grafting, indicating comparable levels of grafting has been achieved. The two samples also exhibited good adhesion. The results were also compared to the unmodified YO22 polypropylene which did not undergo grafting and exhibited poor adhesion. Hence, despite some degree of degradation, which is inevitable, a good level of grafting and adhesion was still achieved.

(139) FIG. 20 compares the level of grafting for all of the production run samples. After normalizing against the internal standard (and offsetting for clarity), the level of grafting for each sample appears similar. This provides validation of the consistency and quality of the processing conditions used to perform the grafting.

(140) (d) Adhesion Performance

(141) Peel adhesion measurements of the grafted polypropylene were determined using the peel test. All measurements are an average from three coupons. As can be seen from FIG. 21, excellent adhesion was achieved with all the production run samples, which was well above the target adhesion value of the DIN 30678 PP industry standard.

Example 7

Blending with Self-Healing Agent

(142) (a) Characterization of Healing

(143) Nucrel 2940, a polyethylene-co-methacrylic acid copolymer, was tested as the healing agent. 2 wt % Luperox and MAH were fed from a micro-hopper (or feeder) and combined with ETILINAS LL0209AA polyethylene (LLDPE) fed from a separate hopper at the same time in a twin screw extruder. 5 wt % Nucrel 2940 was added in a second extrusion run through a single screw extruder to form 5 wt % Nucrel-modified MAH-grafted LLDPE. The healing agent (Nucrel 2940) was then blended with the 5 wt % Nucrel-modified MAH-grafted LLDPE at ratios of 2:1, 1:1 and 1:2 by weight in a third extrusion run through the single screw extruder under the following conditions: Single Screw Extruder Type: AXON ab PLASTMASKINER SINGLE SCREW COMPOUNDER: L:D ratio of 38:1, 18 mm Screw Diameter, 3 mm strand diameter die Melt Temperature: 230-236 C. Temperature Profile (Zones 1 to 6): 170 C., 175 C., 180 C., 180 C., 180 C., 180 C. Melt Pressure: 596-745 PSI Screw Speed: 72 rpm Motor Current: 0.1 Amp

(144) Using the above method, all the components were melted together and upon cooling, form a self-healing adhesive blend with a microstructure where the healing agent is dispersed as particles within the 5 wt % Nucrel-modified MAH-grafted LLDPE.

(145) The self-healing adhesive blend was then used as the adhesive layer between a topcoat layer and a primer layer in a coating for the peel test coupons. The coupons were subjected to consecutive peel tests. After the first peel test, the topcoat was put back onto the primer surface and held in place using a clamp with up to 120 N force and then heated to 110 C. for 1 hr before the coupon was subjected to the next peel test. Healing efficiency was determined by comparing the initial peak load prior to crack propagation of the virgin material against the peak load of the healed material.

(146) The conditions above were varied by increasing the clamping pressure to 240 N as well as heating the topcoat to 120 C. for 1 hr. The data is shown in FIGS. 22(a), (b) and (c) for the 1:2, 1:1 and 2:1 (healing agent:grafted adhesive) formulations. A summary of the results is also set out in Table 5.

(147) TABLE-US-00005 TABLE 5 Healing results at various ratios of healing agent:grafted adhesive and various healing methods Formulation (Healing Load agent:LLDPE) Healing method Virgin Healed Efficiency 1:2 Standard 166.2 23.1 13.9 1:2 Increased 193.7 51.7 26.7 Pressure 1:2 Increased 220.6 85 38.5 temperature 1:1 Standard 156.7 103.4 66.0 1:1 Increased 138.3 100.5 72.7 Pressure 1:1 Increased 88.48 73.9 83.5 temperature 2:1 Standard 131.3 107.1 81.6 2:1 Increased 57.9 57.5 99.7 Pressure 2:1 Increased 50.6 46.3 91.5 temperature Standard conditions: 120N force applied and heated to 110 C. for 1 hr Increased pressure: 240N force applied and heated to 110 C. for 1 hr Increased temperature: 120N force applied and heated to 120 C. for 1 hr

(148) From the above results, it can be seen that: 1) increasing temperature and pressure increased the healing efficiency to almost 100% if higher concentrations of the healing agent is used; 2) increasing temperature resulted in a larger beneficial effect because a slight increase of 10 C. from 110 C. to 120 C. increased healing efficiency from 13.9 to 38.5 (1:2 formulation) and from 66.0 to 83.5 (1:1 formulation), while doubling the pressure from 120N to 240N only increased the healing efficiency from 13.9 to 26.7 (1:2 formulation) and from 66.0 to 72.7 (1:1 formulation); 3) increasing the concentration of the healing agent had a significant impact on healing efficiency; 4) increasing the pressure only significantly increased the healing efficiency if the concentration of the healing agent was higher than that of the grafted adhesive.

(149) FIG. 23 shows the results of healing efficiency for a range of formulations with varying concentrations of the healing agent (Nucrel) and healing conditions. A continuous decrease in healing was observed as the level of healing agent was reduced. This was regardless of the healing conditions. No healing was achieved in the absence of the healing agent (Nucrel).

(150) Thermal analysis of the formulations was performed to elucidate the healing mechanism. FIG. 24 shows the results of differential scanning calorimetry (DSC) analysis. The addition of Nucrel 2940, which has a melting point of about 90 C., would have been expected to reduce the melting point of the grafted polyethylene significantly through blending. However, the DSC results in FIGS. 24 and 25 show that the glass transition temperature of the adhesive is relatively unaffected by blending. This indicates that plasticization of the adhesive did not occur. It is also seen that, as higher ratios of the healing agent was blended with the adhesive, there was an observable second endothermic region in the temperature range of 80 C. to 90 C. (FIG. 24). This indicates that the blended formulation exists as two separate immiscible phases.

(151) The SEM images of FIG. 26 show the fractured surface of the same blends. These provide further support for the lack of plasticization and confirm the presence of a biphasic structure in the polymer formulation. The Nucrel 2940 is clearly not miscible with the grafted polyethylene as a two-phase microstructural morphology is present.

(152) As a result of the biphasic system, it is envisaged that an increase in pressure due to expansion of the healing agent from heat and the external pressure applied drives the healing agent into a damaged zone to rejoin the two surfaces. This allows the healing of the damaged zone through a pressure delivery mechanism, which is schematically shown in FIG. 27. As seen in FIG. 26, observation of the difference in surface roughness between the phase separated Nucrel particles and the grafted polyethylene suggests that the healing present in these systems may arise from the phase separated Nucrel particles adhering to both the primer and the topcoat layers. The phase separation of the Nucrel from the grafted polyethylene adhesive may have resulted in increased mobility during healing and supports the postulated pressure delivery mechanism. The observation also suggests that the microstructure of large phase separated particles may facilitate a sufficient amount of the healing agent to flow into a damaged zone when a stimulus such as heat is applied.

(153) (b) Additives

(154) Pimelic acid and citric acid were tested as modifiers in the self-healing formulation. 2 wt % and 20 wt % of the Nucrel phase was replaced with the modifiers and healing of the interface was assessed. FIG. 28 shows the surfaces after healing for the 10 wt % modified samples compared with the unmodified mendable formulation. A plethora of bubbles on the surface of the modified samples were observed. In particular, very large bubbles were observed on the surface for the 10 wt % pimelic acid modified formulation.

(155) The data showing the actual load versus extension before and after healing for the pimelic acid and citric acid modified systems are shown in FIGS. 29a and 29b, respectively. It can be observed that cohesive failure after healing was evident for each system as seen from the 2 wt % modified systems as shown in FIG. 30, which compares well with the unmodified adhesive.

(156) Formulations where decreasing concentrations of the healing agent blended with the MAH-grafted polymer, and decreasing concentrations of healing agent blended with the MAH-grafted polymer which further comprised pimelic acid or citric acid were prepared as follows:

(157) TABLE-US-00006 TABLE 6 Samples with varying concentrations of the Nucrel 2940 (healing agent) from 10 wt % to 67 wt % % Nucrel 2940 % MAH-grafted polymer 10 90 20 80 33 67 50 50 67 33

(158) TABLE-US-00007 TABLE 7 Samples with varying concentrations of the Nucrel 2940 (healing agent) from 8 wt % to 50 wt %, and 2 wt % of pimelic acid % Nucrel 2940 % Pimelic Acid % Adhesive 50 0 50 48 2 50 38 2 60 28 2 70 18 2 80 8 2 90

(159) TABLE-US-00008 TABLE 8 Samples with varying concentrations of the Nucrel 2940 (healing agent) from 18 wt % to 50 wt %, and 2 wt % of citric acid % Nucrel 2940 % Citric Acid % Adhesive 50 0 50 48 2 50 38 2 60 28 2 70 18 2 80 8 2 90

(160) The load versus extension data and peak load data of these formulations were analyzed and shown in FIGS. 31, 32 and 33.

(161) FIG. 32a shows the load versus extension data of formulations comprising 8 wt % to 50 wt % Nucrel 2940. The erratic nature of the data is typical of cohesive failure. When the maximum loads before and after healing are shown, as can be seen in FIG. 32b, the benefits of adding the pimelic acid are more evident. It can be seen that Nucrel 2940 was able to function as an effective healing agent for all samples regardless of its concentration. However, below 28 wt % of Nucrel 2940, the level of adhesion had decreased, which compromised only the static properties and not the mendability. Similar results were obtained for the citric acid modified system (as can be seen in FIG. 33) with excellent healing efficiency being achieved across the range of Nucrel 2940 concentrations used apart from the lowest concentration of Nucrel 2940.

(162) FIGS. 34, 35 and 36 show the effect of reducing Nucrel 2940 concentration and changing the modifier from citric acid to pimelic acid using optical or scanning electron microscopy. It can be seen that each primer surface showed extensive evidence of cohesive failure, but also a plethora of bubbles. This was evident at different Nucrel 2940 concentrations for both pimelic acid and citric acid modified samples. The scanning electron microscopic images show the presence of these bubbles, further confirming the pressure delivery healing mechanism. Extensive phase separation of the modifier from the continuous adhesive matrix was also observed, which indicates that the Nucrel 2940 has higher mobility because it is present in an undiluted state in the matrix. This means that when thermal energy is applied, it is able to flow into a cavity. After cooling, it can be seen that the phase separated particles were able to adhere to the epoxy primer, as evidenced by thermoplastic tearing observed on the surface. The pressure delivery healing mechanism further enhances this mobility by pushing the healing agent into a cavity.

(163) DSC analysis shown in FIG. 37 for the pimelic acid and citric acid modified formulations show little change in the melting point for all of the formulations evaluated. This indicates that the Nucrel 2940 healing agent does not plasticize the polyethylene matrix and is therefore present in a phase separated microstructure. Without being bound by theory, this suggests that the phase separated Nucrel 2940 with enhanced mobility provides the primary driving force for healing during thermal activation.

(164) Ethylene vinyl acetate (EVA) was also investigated as a healing agent. In this case, the grafted adhesive was kept at a constant concentration but the ratio of EVA to Nucrel 2940 was systematically varied, from 50/0, 40/10, 25/25, 10/40 to 0/50 of EVA/Nucrel 2940. Data on load versus extension are shown in FIG. 38, while the peak loads before and after healing are shown in FIG. 39. The peak load plots clearly show that EVA is an effective healing agent. Scanning electron images of the failure surface shown in FIG. 40 illustrate the presence of the pressure delivery healing mechanism as evidenced by the plethora of bubbles on the surface. This indicates that a number of chemical interactions occurred between the matrix and the EVA which facilitate the healing mechanism.

Applications

(165) Preparation of polyethylene and polypropylene adhesives, which incorporate a self-healing function, have been demonstrated. The self-healing function is capable of being repeated to restore adhesive performance after damage.

(166) The self-healing polymer materials or composite materials thereof have applications for use in self-healing the coatings of pipelines (such as those for transport of oil and gas products), light weight construction structures where durability is required (such as in aerospace and aircraft parts and components), vehicle components, and components for marine use, bridge pipes and energy production (such as wind turbines and blades).

(167) It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.