Process for fabricating polymeric articles

Abstract

A process for the production of a polymeric article directed to (a) forming a ply having successive layers, namely, (i) a first layer made up of strands of an oriented polymer material; (ii) a second layer of a polymeric material; (iii) a third layer made up of strands of an oriented polymeric material, wherein the second layer has a lower peak melting temperature that of the first and third layers; (b) subjecting the ply to conditions of time, temperature, and pressure sufficient to melt a proportion of the firsts layer to melt the second layer entirely, and to melt a proportion of the third layer, and to compact the ply; and (c) cooling the compacted ply. The resultant articles have good mechanical properties yet may be made at a lower compaction temperature than articles not employing the second layer, leading to a more controllable manufacturing process.

Claims

1. A polymeric article comprising a ply of at least three layers, the at least three layers comprising, in sequence, a first layer composed of strands of a first polymeric material, a second layer composed of a second polymeric material, and a third layer composed of strands of a third polymeric material, wherein the polymeric material of each of the three layers has a melting temperature and the second polymeric material has a degree of polymeric orientation less than that of the strands of the first and third polymeric materials; wherein the first and third layers are fabrics which are woven or knit from tapes, fibre yarns, or filament yarns; wherein a portion of each of the at least three layers has been melted; wherein each of the at least three layers comprises the same chemical class of polymer, the chemical class of polymer selected from the group consisting of polyethylene, polypropylene, polyoxymethylene, blends thereof, copolymers thereof, and mixtures thereof; wherein the second layer comprises a lower melting temperature than that of the first and third layers; wherein the melting temperature of the second layer is at least 5 C. lower than the melting temperature of the first and third layers; and wherein one of the at least three layers was biaxially oriented prior to being melted.

2. The polymeric article of claim 1 wherein the chemical class of polymer comprises polypropylene.

3. The polymeric article of claim 1 wherein the chemical class of polymer comprises a blend of polypropylene and polyethylene.

4. The polymeric article of claim 1 wherein the second layer has a thickness less than that of either the first layer or the third layer.

5. The polymeric article of claim 1 wherein each of the at least three layers has a substantially identical thickness.

6. The polymeric article of claim 1 wherein the second layer has a thickness greater than that of either the first layer or the third layer.

7. The polymeric article of claim 1 wherein at least one of the at least three layers comprises multiple layers.

8. A polymeric article comprising a ply of at least three layers, the at least three layers comprising, in sequence, a first layer composed of strands of a first polymeric material, a second layer composed of a second polymeric material, and a third layer composed of strands of a third polymeric material, wherein the polymeric material of each of the at least three layers has a melting temperature and the degree of polymeric orientation of the second polymeric material is less than that of the strands of the first and third polymeric materials; wherein the first and third layers are fabrics which are woven or knit from tapes, fibre yarns, or filament yarns; wherein a portion of each of the at least three layers has been melted; wherein each of the at least three layers comprises the same chemical class of polymer, the chemical class of polymer selected from the group consisting of polyethylene, polypropylene, polyoxymethylene, blends thereof, copolymers thereof, and mixtures thereof; wherein the second layer comprises a lower melting temperature than that of the first and third layers and is melted to a greater degree than the first and third layers; wherein the melting temperature of the second layer is at least 5 C. lower than the melting temperature of the first and third layers; and wherein the second layer is not oriented.

9. The polymeric article of claim 8 wherein the chemical class of polymer comprises polypropylene.

10. The polymeric article of claim 8 wherein the chemical class of polymer comprises polypropylene and polyethylene.

11. The polymeric article of claim 8 wherein the second layer has a thickness less than that of either the first layer or third layer.

12. The polymeric article of claim 8 wherein each of the at least three layers has a substantially identical thickness.

13. The polymeric article of claim 8 wherein the second layer has a thickness greater than that of either the first or third layer.

14. The polymeric article of claim 8 wherein at least one of the at least three layers comprises multiple layers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described in more detail with reference to the accompanying drawings, in which:

(2) FIG. 1 is a graph of tensile modulus versus temperature;

(3) FIG. 2 is a graph of peel strength versus temperature;

(4) FIG. 3 is a graph of tensile strength versus temperature;

(5) FIG. 4 is a graph of performance index versus temperature;

(6) FIG. 5 is a graph of peel strength versus temperature;

(7) FIG. 6 is a graph of tensile modulus versus temperature;

(8) FIG. 7 is a graph of tensile strength versus temperature;

(9) FIG. 8 is a graph of performance index versus temperature;

(10) FIG. 9 is a low magnification micrograph (50) showing the sample edge and fracture structure;

(11) FIG. 10 is a micrograph of the sample of FIG. 9 (30) showing the peel fracture surface for the sample made at 175 C. without a film.

(12) FIG. 11 is a low magnification micrograph (50) of the sample edge;

(13) FIG. 12 is a micrograph of the sample of FIG. 11 (30) showing surface damage associated with the interface where the film was located;

(14) FIG. 13 is a low magnification micrograph (50) showing the sample edge and fracture surface.

(15) FIG. 14 is a micrograph of the sample of FIG. 13 (30) showing the peel fracture surface for the sample made at 191 C. without a film.

(16) FIG. 15 is a low magnification micrograph (50) of the sample edge;

(17) FIG. 16 is a micrograph is the sample of FIG. 15 (30) showing that a sample made at 191 C. with a film develops surface damaging on peeling;

(18) FIG. 17 is a micrograph (30) showing a peel fracture surface from a sample made at 193 C. without a film.

(19) FIG. 18 is a micrograph of the sample of FIG. 17 (30) showing regions where there has been cohesive failure at the film/tape interface;

(20) FIG. 19 shows the results for both the flexural modulus and flexural strength for example set E;

(21) FIG. 20 and FIG. 21 are views of a corresponding peel tested product that have two and three layers of the 100GA02 polymer film, respectively;

(22) FIGS. 22-25 show low magnification micrographs of typical fracture surfaces from samples made without a film at 135, 148, 152, and 154 C., respectively;

(23) FIGS. 26-29 are four micrographs showing samples made with a film at 135, 148, 152, and 154 C., respectively;

(24) FIG. 30 is at 135 C. with no film;

(25) FIG. 31 is at 135 C. with film;

(26) FIG. 32 is at 148 C. with no film;

(27) FIG. 33 is at 148 C. with film;

(28) FIG. 34 is at 152 C. with no film;

(29) FIG. 35 is at 152 C. with film;

(30) FIG. 36 is at 154 C. with no film;

(31) FIG. 37 is at 154 C. with film.

DETAILED DESCRIPTION OF THE INVENTION

(32) The invention will now be further exemplified, with reference to the following examples, set out in sets.

(33) In these examples standard test methods were used.

(34) Tensile modulus and tensile strength were determined following the protocols of ASTM D638. Flexural strength was determined following the protocols of ASTM D790.

(35) Peel strength was determined by the protocols of the T-Peel test, ASTM D1876. Samples for testing were 10 mm wide and 100 mm long and were tested using a crosshead speed of 100 mm/min. The testing was carried out parallel to the warp direction.

(36) In all cases three samples were tested and the results averaged.

(37) The percentage of material melted was determined by Differential Scanning calorimetry (DSC) carried out at a heating rate of 10 C./min.

Example Set A

(38) Fabric layers were woven, in a plain weave, from CERTRAN, a 250 denier multifilament yarn of melt spun filaments of oriented homopolymeric polyethylene available from Hoechst Celanese, and characterised as follows:

(39) TABLE-US-00001 TABLE 1 Molecular weight Breaking Tensile initial Modulus (Mw) (Mn) strength (GPa) secant (GPa) 2% (GPa) 130,000 12,000 1.3 58 43

(40) Samples, using two layers of woven cloth, were processed in a hot press using a two stage pressure process. An initial pressure of 0.7 MPa (100 psi) was applied while the assembly reached the compaction temperature. After a 2 minute dwell time at this temperature, a higher pressure of 2.8 MPa (400 psi) was applied for 1 minute upon which time the assembly was cooled at a rate of approximately 20 C. per minute to 100 C. Samples were made under three conditions. Firstly, standard compaction at a temperature of 138 C. Secondly, a layer of the LDPE film was laid between the two layers of woven cloth and then processed at 126 C. (above the melting point of the film but below the melting point of the oriented fibres). Finally a sample was made by interleaving one layer of the LDPE film between the two layers of woven cloth and processing at a temperature of 136 C.

(41) The results of these tests are shown in the table below.

(42) TABLE-US-00002 TABLE 2 Compaction % fibre Peel Tensile temperature melted strength modulus Sample ( C.) material (N/10 mm) (GPa) Standard compaction 138 26 7.2 9.2 technique (comparison) Woven PE cloth + 126 0 6.8 3.1 interleaved LDPE film (comparison) Woven PE cloth + 136 14 11.2 8.1 interleaved LDPE film

(43) For the standard compaction technique without the film, a compaction temperature of 138 C. was found to be optimum for giving a good modulus and reasonable level of interlayer bonding (peel strength). This optimum temperature was very close to the point where major crystalline inciting occurred, at 139 C. Using an interleaved film, but processing at 126 C., just enough to completely melt the interlayer film, but not the surfaces of the fibres, good interlayer bonding was developed but modulus was poor due, presumably, to poor interfibre bonding as it will be difficult for the molten material to penetrate the fibre bundles. Finally, the sample made with the interlayer film but processed at 136 C., where selective inciting of the oriented fibres occurred, shows the highest peel strength and a good modulus. In addition, those properties were obtained at a temperature 2 C. below the temperature required for compaction without the film, widening the processing window as there is less risk of over melting at a temperature of 139 C.

Example Set B

(44) In these examples partially melted monolithic articles were prepared, using TENSYLON oriented polyethylene tape produced by Synthetic Industries, USA, having the following characteristics:

(45) TABLE-US-00003 TABLE 3 Tensile strength 1.5 GPa Tensile modulus 88 GPa Denier 720

(46) This was woven into a fabric. For the interlayer a polyethylene of closely similar type was obtained, FL5580 film grade from Borealis A/S, Denmark, melting point 130 C. This was extruded into a film approximately 10-15 m in thickness, using a standard film extruder and film die.

(47) Compaction experiments were carried out at a range of temperatures between the melting point of the film (approximately 130 C.) up to and including the normal compaction range for this material (148156 C.). The woven cloth was thin (areal density 83 g/m.sup.2) and to obtain an even pressure over the assembly during compaction rubber sheets were used inside the normal metal plates utilised for compaction, with soft aluminum foils between the rubber sheets and the ply being compacted. Dwell time was 5 minutes. Cooling was 20 C./min.

(48) In the first series of tests, samples were compacted over the temperature range 148 to 156 C., with and without the interleaved film. FIGS. 1, 2 and 3 show the tensile modulus, peel strength and tensile strength of these samples.

(49) It will be seen from FIG. 1 that when an interlayer is used, the tensile modulus shows a monotonic decrease with temperature, as opposed to the peak seen with normal compaction. We infer that the interlayer is producing higher levels of bonding at low compaction temperatures making the properties less sensitive to the amount of melted material produced.

(50) The peel strength of the interleaved film samples (FIG. 2) is higher throughout the temperature range, compared to normal compaction.

(51) The tensile strength (FIG. 3) was similar for the two samples; concern that this property might be compromised by use of the interlayer was allayed.

(52) We have developed a performance index (PI) in an attempt to discern the optimum combination of the compacted sheet properties. If we consider the tensile modulus E, the tensile strength c and the peel strength, Peel, assuming each property is equally important, this is defined as follows:
PI=100[(E.sub.T/E.sub.max)+(.sub.T/.sub.max)+(Peel.sub.T/Peel.sub.max)]/3
where the subscript T refers to a particular compaction temperature and the subscript max refers to the maximum value measured for all the samples. Values of the performance index are shown below in FIG. 4. From this it is seen that the interlayer samples show a less variable combination of properties, in particular having better properties at lower compaction temperatures, than corresponding samples without an interlayer. This confirms the view that a lower compaction temperature can be used when an interlayer is employed, giving processing advantages.

Example Set C

(53) The tests of this example employed the same materials, equipment and techniques as Example Set B. It provides a comparison of the properties of compacted sheets made at three temperatures: a normal compacted sample made at the standard optimum temperature of 154 C., an interlayer sample made at 152 C. and a comparison interlayer sample made at 135 C., which is enough to melt the interlayer but not any part of the TENSYLON tapes. The results are shown below.

(54) TABLE-US-00004 TABLE 4 Assembly Peel Tensile Tensile Sample temperature strength modulus strength configuration ( C.) (N/10 mm) (GPa) (MPa) Standard 154 10 + 2.7 29.6 + 3.9 535 + 55 compaction technique (comparison) Woven PE 152 10.6 + 1.5 26.8 + 1.6 483 + 28 cloth + interlayer Woven PE 135 5.9 + 0.9 14.5 + 2.7 283 + 25 cloth + interlayer (comparison)

(55) Compacting at a temperature just above the melting temperature of the interlayer but below the melting range of the oriented tapes (135 C.) gives modest mechanical properties. The sample made at 152 C. with the interlayer shows comparable values of tensile modulus, strength and peel strength, compared with the normal compacted sample made at 154 C. Using the film therefore gives the prospect of lowering the compaction temperature 2 C., increasing the width of the processing window.

Example Set D

(56) Tests were carried out to investigate the impact of using interleaved layers of polypropylene (PP) film in combination with the normal layers of woven PP tapes. The PP film this time was the same polymer grade as used for the drawn and woven tapes. The polymer, grade 100GA02, was obtained from BP Chemicals, Grangemouth, UK.

(57) The film had the following properties:

(58) Mn=78,100

(59) Mw=360,000

(60) Density=910 Kg/m.sup.3

(61) It was extruded using a Brabender single screw extruder and a standard film die set to a temperature of 260 C. Extrusion screw and wind up speeds (8 rpm and 4.6 m/min) were chosen such that a film thickness of approximately 15 m was produced.

(62) The next stage in the study was to manufacture a range of samples, with the film as an interlayer, and without (comparison), to assess the impact of an interlayer on compacted sheet properties. DSC tests, carried out a heating rate of 10 C./min, showed that the peak melting point of the film was 162 C., while the constrained peak melting point of the oriented tapes was 194 C. Compacted samples were therefore made at a temperature of 175 C., high enough to melt the film completely but not high enough to cause any melting of the oriented phase.

(63) The material used was a fabric woven tape, formed from a slit film, draw ratio nominally 10:1, woven in a 6060 style. A single pressure process (4.6 MPa) with a dwell time of 5 minutes was used. Samples were also compacted at 180, 187, 189, 191, 193, 195, 197 and 200 C. Cooling rate was 50 C./min, achieved by passing cold water through the heating platens.

(64) In the first set of tests, 4 layer samples were made for measurement of the interlayer bond strength, using the peel test. The results are given in FIG. 5.

(65) It is seen that at all compaction temperatures, the peel strength is higher when using the interlayer.

(66) The next stage was to measure the stress-strain behaviour of various materials to see if these had been reduced in any way.

(67) The results are shown in FIGS. 6 and 7.

(68) As shown in FIG. 6, within the experimental scatter no significant difference was seen between the initial tensile modulus of the two groups of samples. The modulus is seen to be relatively constant between 191 and 197 C. for both sets of samples. Thus in this set of tests the introduction of a thin film of material between the woven layers has no discernible detrimental effect on the compacted sample modulus.

(69) For the tensile strength results shown in FIG. 7 there was a clearer difference seen between the two sets of samples. Here the samples made with the film showed a higher tensile strength than those compacted normally. This difference is largest at the lower temperatures when there is little surface melting of the oriented tapes. However, even in the optimum compaction range, the film samples still show a slightly higher tensile strength.

(70) The table below presents a summary of the results from the tensile and peel strength tests (ASTM protocols as noted above), in respect of peel strength, tensile modulus, tensile strength and failure strain.

(71) In an attempt to discern the optimum combination of the four parameters mentioned above, and help assess the impact of the interleaved film, the following performance index (PI) was derived. Assuming each property tested is equally important, this is as follows
PT=100[(E.sub.T/E.sub.max)+(.sub.T/.sub.max)+(.sub.T/.sub.max)+(Peel.sub.T/Peel.sub.max)]/4
where the subscript T refers to a particular compaction temperature and the subscript max refers to the maximum value measured for all the samples. Values of the performance index are also shown in the table below and in FIG. 8. It is seen that the interlayer samples have a better balance of properties compared to the normal samples when analysed in this way, but with the peel strength showing the most marked improvement.

(72) It will be seen that the PI value of the samples made in accordance with the invention, employing a film as interlayer, exceeded the corresponding no film value at each given compaction temperature. The best performance was achieved when some melting of the woven fabric took place, notably at a compaction temperature of around 189-197 C. The PI value was higher in the interlayer sample.

(73) TABLE-US-00005 TABLE 5 Compaction Tensile Tensile Peel Performance temperature modulus strength Failure strength Index ( C.) E (GPa) (MPa) strain (N/10 mm) (PI) No film 175 2.99 67 5 0.63 38 180 2.31 93 12 1.17 46 187 2.24 123 15 1.89 55 189 2.87 148 18 3.7 69 191 3.41 154 18 4.98 76 193 3.43 155 15 7.53 77 195 3.4 138 21 7.2 80 197 3.39 137 20 >7.2* 79 200 1.4 29 20 >7.2* 49 with film 175 3.09 100 7 5.21 53 180 2.59 155 16 6.23 70 187 2.47 145 17 8.66 72 189 3.1 163 18 11 84 191 3.13 168 18 12.3 87 193 3.18 173 20 13.7 93 195 3.44 150 19 16.6 94 197 3.49 136 20 >16.6* 94 200 1.4 29 20 >16.6* 63 *samples too well bonded to be tested in peel test comparisons
SEM Images of Polypropylene Peel Fracture Surfaces

(74) The samples compacted at 175, 191 and 193 C. were selected for SEM microscopy of their fracture surfaces following peel testing. The samples were as follows.

(75) TABLE-US-00006 TABLE 6 Sample Compaction temperature ( C.) Details comparison 175 No film comparison 175 1 layer 100GA02 comparison 191 No film invention 191 1 layer 100GA02 comparison 193 No film Invention 193 1 layer 100GA02

(76) The measured peel strengths for these samples are as shown in the Table below.

(77) TABLE-US-00007 TABLE 7 Compaction temperature ( C.) Without film With film 175 0.63 + 0.12 5.21 + 0.98 191 4.98 + 1.6 12.3 + 4.1 193 7.53 + 3.52 13.7 + 3.5
Peel Fracture Loads (N/10 mm)

(78) The associated SEM micrographs are FIGS. 9-18. Comments on these micrographs are as follows.

(79) 175 C.No Film

(80) FIG. 9: This is a low magnification micrograph (50) showing the sample edge and fracture surface. The key point is that at this compaction temperature of 175 C., the tapes and the layers are very poorly bonded.

(81) FIG. 10: This micrograph (30) shows the peel fracture surface for the sample made at 175 C. without a film. There is very little surface damage. As will be seen from the later micrographs, the amount of surface damage correlates very well with the peel strength, as being evidence of the amount of energy needed to separate the surfaces. If the woven layers are poorly bonded, the failure proceeds between the layers causing little damage and a low peel load. If the layers are well bonded, the failure path has to move into the oriented tapes, or the film layer, which increases the peel load and the samples then show a much rougher surface appearance.

(82) 175 C.with Film

(83) FIG. 11: This is a low magnification micrograph (50) of the sample edge. It is seen again, that at this temperature the layers and tapes are in general poorly bonded.

(84) FIG. 12: This micrograph (30) shows that there is considerable surface damage associated with the interface where the film was located, which correlates with the measured increase in peel strength. However it is also seen that the tapes themselves are not well bonded to those underneath, i.e. where there is no film. To Summarise175 C. Results

(85) Using a film, and processing at a temperature above the film melting point but below the temperature where the oriented tapes melt, gives a structure which is well bonded where the film is present, but poorly bonded elsewhere. It is clear that it would be very difficult for the film to penetrate through the woven tape layers.

(86) Processing at a temperature well below the melting temperature of the oriented tapes, and using no film, gives poor bonding throughout the structure. 191 C.no Film

(87) FIG. 13: This is a low magnification micrograph (50) showing the sample edge and fracture surface. The key point is that at this compaction temperature of 191 C., where the surfaces of the oriented tapes are now beginning to melt, the layers are now much better bonded and the compacted sheet is more homogeneous. The individual tapes in the compacted sheet are less apparent than at 175 C. (FIG. 10).

(88) FIG. 14: This micrograph (30) shows the peel fracture surface for the sample made at 191 C. without a film. As would be expected, there is increased surface damage compared to the sample made at 175 C. As with most traditionally compacted samples (i.e. without a film) the surface damage is patchy: there are some regions where the damage is pronounced and others where it is less so. 191 C.with Film

(89) FIG. 15: This is a low magnification micrograph (50) of the sample edge. It is seen that at this temperature the layers are well bonded; the structure is now homogeneous.

(90) FIG. 16: This micrograph (30) shows that a sample made at 191 C. with a film develops a large amount of surface damage on peeling, reflecting the higher peel force measured for this sample. The damage is now seen to be more even across the sample surface. Perhaps the introduction of the film at the interlayer is able to even out any local differences in the way the two woven layers fit together. To Summarise191 C. Results

(91) Using a film, and processing at a temperature where the oriented tapes begin to melt, produces the combination of an overall homogeneous structure and interlayer regions (the weak point in the structure) which are very well bonded.

(92) The level of damage (i.e. bonding) is more even over the surface when using an interleaved film

(93) The level of damage for the sample made at 175 C. with a film is similar to that seen for the sample made at 191 C. without a film, reflecting the similarity in the peel load values. 193 C.without Film

(94) FIG. 17: This shows (30) a peel fracture surface from a sample made at 193 C. without a film. The fracture surface shows a similar amount of damage to that on the sample made at 191 C. without the film (FIG. 14) but not as much as that on the sample made at 191 C. with the film. The amount of surface damage correlates well with the measured peel loads. As with the sample made at 191 C. without the film, the damage seen over the area is patchy. 193 C.with Film

(95) FIG. 18: This micrograph (30) which shows regions where there has been cohesive failure within the film and regions of adhesive failure at the film/tape interface. This suggests that the failure could be a combination of these two modes. To Summarise193 C. Results

(96) Using a film, and processing at a temperature where the oriented tapes begin to melt, produces the combination of an overall homogeneous structure and interlayer regions which are well bonded.

(97) The level of damage (i.e. bonding) is more even over the surface when using an interleaved film. It is proposed that the interleaved film is able to more easily fill any gaps which might be present when the woven layers are pressed together.

(98) The level of damage seen on the 193 C. compacted sample fracture surfaces is higher than that on the corresponding 191 C. surfaces (FIGS. 15, 16) reflecting the associated increase in peel strengths.

Example Set E

(99) In this example set the flexural properties of samples compacted at different temperatures, with and without an interlayer, were tested.

(100) The sample preparation was as described previously. The ASTM testing regimes noted above were used.

(101) FIG. 19 shows the results for both the flexural modulus and flexural strength. Below the onset of selective surface melting of the oriented tapes (about 187 C.), the flexural properties of the interleaved film samples are better than the conventionally compacted samples. Above this temperature, the flexural properties of the two sets of samples are very similar. Flexural properties peak at a compaction temperature of 195 C. for both sets of samples.

Example Set F

(102) In this set of tests effect of interlayer thickness was studied, using the same method and polypropylene material as was used in Example Set D. As with the examples above a film of thickness 10-15 pm was used as an interlayer, with 0-3 such films being used, multiple films being placed together in a stack.

(103) Average values for stress-strain behaviour and peel strength are shown below in the following table.

(104) TABLE-US-00008 TABLE 8 Compaction Tensile Tensile Peel Temperature modulus strength strength ( C.) Interlayer (GPa) (MPa) (N/10 mm) 191 C. No film 3.41 + 0.25 154 + 8 4.98 + 1.6 1 layer 3.13 + 0.05 168 + 8 12.3 + 4.1 2 layers 3.17 + 0.15 135 + 9 8.8 + 1.3 3 layers 3.00 + 0.36 137 + 3 12.5 + 4.7 193 C. No film 3.43 + 0.29 155 + 7 7.53 + 3.52 1 layer 3.18 + 0.09 173 + 4 13.7 + 3.5 2 layers 3.22 + 0.18 144 + 5 9.6 + 2.3 3 layers 3.01 + 0.37 160 + 9 11.7 + 4.3

(105) The results indicate that the tensile modulus falls for both temperatures as the film thickness is increased; that the tensile strength peaks for the single layer film thickness and then falls again as the thickness is increased; and that the peel strengths are similar for all layers of film thickness, and all significantly higher than the comparative samples without an interlayer.

(106) The results, taken together, suggest that the single layer is the optimum, giving the maximum increase in peel strength for the minimum loss of tensile modulus, and with retention or slight improvement in tensile strength.

Example Set G

(107) In this example set SEM microscopy was used to study peel fracture surfaces using the same materials and processing as described in Example Set B but having multiple interlayers. The processing temperature was 193 C., so the figures of Example Set D which provide comparisons are FIG. 17 (no film) and FIG. 18 (one layer of film). FIGS. 20 and 21 are views of a corresponding peel tested product, but having two and three layers of the 100GA02 polymer film, respectively. By way of comparison, in the single layer sample of FIG. 18 of Example Set D, one can see the film layers F lying on top of the oriented tapes underneath. In FIG. 20 a sample made with two layers of film the edge of the sample clearly shows the film layer F located within the sample, and the film layer on the peel surface itself. It appears that failure has proceeded at this point predominantly through the film layer. From this micrograph we can see that the damage zone is located within the film layer. FIG. 21 shows a region of the surface showing the thick film layer, now composed of three film layers F. The damage zone is now seen to be much thinner than the overall film thickness.

Example Set H

(108) This example set examined the importance of the type of film used. In some of the tests the interlayer was made from the same polymer as was used to make the oriented tapes (PP 100GA 02 material as described above). In other tests two further interlayer films were investigated, namely.

(109) 1) A (30 m thick) polypropylene film of m.p. 163 C., obtained from ICI.

(110) 2) A PE film made in-house: this employed the Brabender single screw extruder and the same film die used to make the PP film described above. This used a BOREALIS PE (Film grade FL5580) and the final extruded film was between 10 and 15 m thick.

(111) Compaction experiments were carried out using the same woven PP cloth as described above (10:1 drawn tape, 6060 style, 100GA 02 polymer). Experiments were conducted at two compaction temperatures: 175 C., for comparison, enough to melt each film but not enough to melt the surfaces of the oriented materials and 193 C. which is in the optimum value for normal hot compaction

(112) The results axe shown in the table below.

(113) TABLE-US-00009 TABLE 9 Film Peel Sample thick- strength thickness ness E (Gpa) (MPa) (N/10 mm) (mm) m 175 C. no 2.99 67 5 0.6 0.64 10-12 film matching 3.09 100 7 5.2 0.64 30 PP film ICI PP 2.45 86 1.3 0.72 30 film PE film 2.51 92 0.7 0.68 10-15 193 C. no 3.43 155 15 7.5 0.47 film matching 3.18 173 20 13.7 0.51 10-12 PP film ICI PP 3.08 103 23 8.7 0.58 30 film PE film 2.70 113 28 2.3 0.53 10-15 comparisons

(114) The results indicate that the best samples are those made with the matching PP film.

Example Set I

(115) In this example as assessment was made of the application of the invention to polyester (PET) materials.

(116) Woven PET fabric, and polymer of an identical chemical composition, were supplied by KOSA, GmbH and Co. KG.

(117) The polymer and fabric details were as follows

(118) TABLE-US-00010 TABLE 10 Polymer Type T51-IV ~0.85, Mn ~22,500 Fabric weight 200 g/m.sup.2 Oriented shape multifilament bundles 1100 decitex Weave style Plain weave 9/9 threads/cm Peak m.p. 250 C.

(119) PET film (.about.15 m thick) was cast from the polymer using a standard extruder and a film die, A second PET film, of a different chemical composition to the woven cloth, was also used in these tests: this film was slightly biaxially oriented.

(120) The work reported looked at the application of the invention to the woven PET material, both with and without an interleaved film. Samples were made using both films.

(121) The table below shows a comparison between the stress-strain and peel strength behaviour of samples made with and without the film of the same composition at 257, 258 and 259/260 C. As is seen all the samples made with the film showed increased tensile modulus, tensile strength and peel strength over the samples made without the film, at a given temperature.

(122) TABLE-US-00011 TABLE 11 Compaction Tensile Tensile Peel temperature modulus strength strength ( C.) Sample (GPa) (MPa) (N/10 mm) 257 No film 4.51 + 0.18 88 + 18 1.2 + 0.2 Same film 5.69 + 0.52 178 + 16 5.1 + 0.6 258 No film 4.96 + 0.4 120 + 5 2.0 + 0.4 Same film 6.65 + 0.69 175 + 5 5.9 + 1.4 260/259 No film 6.41 + 0.77 138 + 16 7.2 + 1.2 Same film 7.27 + 0.64 188 + 8 6.9 + 0.9 comparisons

(123) As a further experiment samples were also made, using a compaction temperature of 257 C., using no film, and both PET films, and tested in the manner described previously. The results are as follows.

(124) TABLE-US-00012 TABLE 12 Tensile Tensile Peel modulus strength strength Samples (GPa) (MPa) (N/10 mm) No film 4.51 + 0.18 88 + 18 1.2 + 0.17 Different film 6.85 + 0.32 158 + 13 3.9 + 0.6 Same film 5.69 + 0.52 178 + 16 5.1 + 0.6

(125) It can be seen that in this experiment the mechanical properties were significantly boosted by the presence of either film; and that the films gave rise to enhancement of different mechanical properties. Namely the tensile modulus of the sample with the different film is higher than with the identical film, although the tensile strength and peel strength are higher with the identical film.

(126) A significant finding is that these mechanical properties were achieved using a compaction temperature of 257 C. The optimum temperature for compacting PET by the prior method (no film) is regarded as 260 C. With PET the processing window is narrow, which could inhibit the commercialization of hot compaction processes as applied to PET. A lowering of the compaction temperature to 257 C., yet with achievement of good mechanical properties, suggests a significant practical benefit.

Example Set J

(127) SEM Images of Polyethylene Peel Fracture Surfaces

(128) Peel samples were manufactured as described in Example Set B using woven TENSYLON 10:1 PE tapes (6060 style). Samples were made with and without an interleaved film. In these tests a film of the same grade as the oriented tapes was not available and so the Borealis FL5580 material, a similar grade, was sourced.

(129) 8 samples were studied, having been compacted at 135 C., 148 C., 152 C. and 154 C., with and without an interlayer film, and subjected to the peel test.

(130) TABLE-US-00013 TABLE 13 Compaction temperature ( C.) Without Film With film 135 0.72 + 0.31 5.94 + 0.92 148 4.23 + 0.78 9.02 + 1.18 152 5.56 + 1.05 10.6 + 1.5 154 10 + 2.73 13.4 + 3.3 Peel fracture loads (N/10 mm)

(131) The associated SEM micrographs are FIGS. 22-37 herein. Comments on these micrographs are as follows.

(132) FIGS. 22-25: These figures show low magnification micrographs of typical fracture surfaces from samples made without a film at 135, 148, 152 and 154 C. respectively. As the compaction temperature is increased the level of surface damage increases. At the lowest temperature, where there is no surface melting of the PE tapes, there is no bonding of the tapes.

(133) At 148 C., where the surfaces of the tapes are just beginning to melt, the tapes appear better bonded although the peel surfaces are clear of damage.

(134) At 152 C. surface damage has increased, reflecting the increase in the measured peel load. As with the PP studies, the areas of surface damage are variable when a film is not used.

(135) At 154 C. the damage is further increased.

(136) FIGS. 26-29:

(137) These four micrographs show samples made with a film at 135, 148, 152 and 148 C. respectively. All show increased surface damage compared to the equivalent samples made at the same temperature. Unlike the PP studies, the film is still visible on some of the fracture surfaces, particularly at 135 C. As the compaction temperature is increased the amount of damage increases. Only at 154 C. is substantial damage seen within the oriented tapes (i.e. at the temperature where there is substantial surface melting of the tapes).

(138) For the other temperatures the failure mode seems to have occurred at the film/woven cloth surface, i.e. at least partial adhesive failure. The best performance is therefore confirmed as a combination of film melting and melting of the tape outer surfaces.

(139) FIG. 30: 135 C.

(140) no film: shows one tape going underneath another at 90 to it, and confirms no bonding between the tapes at this temperature.

(141) FIG. 31:

(142) 135 C. with film: this high magnification micrograph shows surface damage and tearing of the interleaved film, but that failure has occurred between the film and the woven layer in some instances.

(143) FIG. 32:

(144) 148 C. no film: this micrograph shows a junction between tapes and indicates much better bonding between the tapes. However there is minimal surface damage suggesting the surfaces were fairly easily separated (i.e. low peel strength).

(145) FIG. 33: 148 C. with film: shows increased surface damage but still adhesive failure.

(146) FIG. 34: 152 C. no film: increased surface damage on this sample compared to the lower temperatures made without a film.

(147) FIG. 35: 152 C. with film: shows adhesive failure.

(148) FIG. 36: 154 C. no film: optimum temperature without a film: substantial damage of the oriented tapes produced during peeling.

(149) FIG. 37: 154 C. with film: this sample gave the roughest peeled surface seen, which correlates with the highest peel load measured. At this compaction temperature the failure appears to be cohesive. The piece of film on the left shows evidence of material peeled off the adjoining tape on the other surface.