Rotomoulded articles prepared from a blend of polyethylene powders

Abstract

The present invention discloses the use of a dry blend comprising a polyethylene resin and a functionalized polyolefin or ionomer in a composition with a thermoplastic resin in order to produce a layer that provides adhesion, fire resistance and low permeation rate in a multi layer rotomolded article.

Claims

1. A single layer rotomoulded article prepared from a dry blend of a) from 10 to 90 wt % based on the weight of the blend, of a first composition consisting of from 40 to 90 wt % based on the weight of the first composition of a first powder or micropellets composition consisting of from 50 to 99.9 wt % based on the weight of the first powder of a linear low density ethylene co-polymer and of from 0.1 to 50 wt % of a functionalised polyolefin or an ionomer or a combination thereof and of from 10 to 40 wt % based on the weight of the first composition of a second resin in powder or micropellets form prepared from the or the linear low density ethylene co-polymer wherein the second resin is dry blended with the first resin; b) from 10 to 90 wt % based on the weight of the blend of a second composition prepared from a thermoplastic resin comprising polyamide.

2. A single layer article comprising a powder or micropellets blend comprising: a) from 40 to 90 wt % based on the weight of the blend of a first resin in powder or micropellets composition of from 50 to 99.9 wt % based on the weight of composition a) of a homopolymer of ethylene having a melt index ranging from 0.1 to 50 dg/min and of from 0.1 to 50 wt % based on the weight of composition a) of a functionalised polyolefin or an ionomer or a combination thereof; and b) from 10 to 40 wt % based on the weight of the blend of a second resin in powder or micropellets form prepared from the homopolymer of ethylene; wherein resin powder b) is dry blended with composition powder a), and wherein about 50 wt % of the blend comprises metallocene-catalyzed polyethylene.

3. The single layer article of claim 2 wherein said article is rotomoulded.

4. The single layer article of claim 2 wherein said article is a pipe coating.

5. A single layer article comprising a composition comprising a resin in powder or micropellets form of from 50 to 99.9 wt % based on the weight of the composition of a homopolymer of ethylene having a melt index ranging from 0.1 to 50 dg/min and of from 0.1 to 50 wt % based on the weight of the composition of an ionomer or a functionalised polyolefin and an ionomer, wherein the resin is dry blended with a second resin in powder or micropellets, and wherein the second resin comprises the homopolymer of ethylene; and wherein about 50 wt % of the composition is metallocene catalyzed polyethylene.

6. The single layer article of claim 5 wherein the composition comprises the ionomer and a grafted polyethylene.

7. The single layer article of claim 5 wherein said article is rotomoulded.

8. The single layer article of claim 5 wherein said article is a pipe coating.

9. The single layer article of claim 2, wherein the homopolymer of ethylene has bimodal or multimodal molecular weight distribution.

10. The single layer article of claim 5, wherein the homopolymer of ethylene has bimodal or multimodal molecular weight distribution.

11. The single layer rotomoulded article of claim 1, wherein about 50% of the weight of the polyethylene in the blend is metallocene-catalyzer polyethylene.

Description

LIST OF FIGURES

(1) FIG. 1 represents the ignition time expressed in seconds for rotomoulded articles of specified wall thicknesses and resin composition.

(2) FIG. 2 represents a two-layer rotomoulded article wherein the inside layer is prepared from polyamide resin R11 and the outside layer is prepared from resin R9 that is a powder blend according to the present invention. The interface between both layers is perfect.

(3) FIG. 3 represents a two-layer rotomoulded articles wherein the inside layer is prepared from polyamide resin R11 and the outside layer is prepared from resin R4 that is a conventional blend of metallocene-prepared polyethylene with a functional polyolefin. Air bubbles are trapped between the two layers especially in sharp angles.

(4) FIG. 4 represents the adhesion level expressed in N/cm for two-layer rotomoulded articles wherein the inside layer is prepared from polyamide resin R11 and the outside layer is a blend as indicated on the figure.

(5) FIG. 5 represents the surface energy expressed in mJ/m.sup.2 for several resins or resin compositions as indicated on the figure.

(6) FIG. 6(a) represents the energy curve for a two-layer rotomoulded article according to the present invention wherein the horizontal axis is the displacement expressed in mm and the vertical axis is the load expressed in newtons

(7) FIG. 6(b) represents the energy curve for a rotomoulded article prepared from cross-linked polyethylene wherein the horizontal axis is the displacement expressed in mm and the vertical axis is the load expressed in newtons.

EXAMPLES

(8) Several rotomoulded articles were prepared as follows.

(9) All test mouldings were carried out on the ROTOSPEED rotational moulding machine. It is a carrousel-style machine with offset arm, LPG burner arm with a burner capacity of 523 kW/hr, air fan cooling, and/or water spray cooling and a maximum plate diameter of 1.5 m.

(10) An aluminum box mould was used to produce the test mouldings. The mould was equipped with a draft angle to facilitate demoulding and the bi-layer articles were prepared by the use of a drop box. The drop box was filled with the material needed for the first layer and then attached to the lid of the mould. A pneumatic ram in the drop box held the material in place until the required temperature was reached, the ram was then activated and the material was dropped in. That operation was repeated for each layer under the conditions described below.

(11) The tests were carried out on several types of resin compositions. The mould was removed from the oven at different peak internal temperatures. The moulding conditions for the trials were as follows: oven temperature: 300° C. rotation ratio: 4:1 cooling medium: water preheated arm and mould rotolog unit n°5/rotolog software version 2.7.

(12) Layer A was prepared from various blends according to the present invention wherein the base resin was a metallocene-produced polyethylene (mPE). The metallocene catalyst component was isopropylidene bis(tetrahydroindenyl) zirconium dichloride. For comparison several resins or resin compositions typically used in rotomoulding applications were also used.

(13) The functionalised polyolefin was a functionalised PE or an ionomer.

(14) Layer B was prepared with a polyamide resin.

(15) All the resins or resin compositions are described in Table I.

(16) TABLE-US-00001 TABLE I Resin mPE resin Composition Form R1 M4043UV ®* 85 wt % mPE + 15 wt % powder Orevac ®18380# R2 M3583UV ®* 85 Wt % Mpe + 15 Wt % powder Orevac ® 18380# R3 M4043UV ®* 95 wt % mPE + 5 wt % powder Orevac ® C306# R4 M4043UV ®* 95 wt % mPE + 5 wt % powder Priex ® 12031.sup.a R5 M4043UV ®* 95 wt % mPE + 5 wt % powder Priex ® 30101.sup.a R6 M4043UV ®* 95 wt % mPE + 2.5 wt % powder Priex ® 12031.sup.a + 2.5 wt % Priex ® 30101.sup.a R7 M4043UV ®* 97 wt % mPE + 3 wt % micropellets Priex ® 12031.sup.a R8 M4043UV ®* 50 wt % R7 + 50 wt % R10 Blend micropellets powder R9 M4043UV ®* 50 wt % R6 + 50 wt % R10 powder R10 M4043UV ®* — powder R11 PA11 Rilsan ®# — R12 XL4008 ®.sup.$ — *Produced by TOTAL Petrochemicals #Produced by Arkema .sup.$Cross-linked PE resin produced by Matrix Polymers .sup.aproduced by Solvay.

(17) Resin mPE was a linear low density polyethylene (LLDPE) having a melt flow index of 4 dg/min, a melting temperature Tm of 120° C. and a vicat temperature Tv of 83° C.

(18) Fire Resistance.

(19) Single-layer articles were produced respectively with resins R6, R10, R11 and R12 in order to assess the fire resistance. The rotomoulded articles were prepared as follows: A1 was prepared with resin R6 and had a 4 mm wall thickness; A2 was prepared with resin R10 and had a 7 mm wall thickness; A3 was prepared with resin R10 and had a 11 mm wall thickness; A4 was prepared with resin R11 and had a 6 mm wall thickness; A5 was prepared with resin R12 and had a 6 mm wall thickness;

(20) The fire resistance was measured following the method of standard test ISO 5660-1. It is a cone calorimeter method using the Fire technology ConeCalc software. The test conditions are: surface area of 100 cm.sup.2 heat flux of 60 kW/m.sup.2 horizontal.

(21) The quantities that were measured: time to ignition in seconds; heat released in kW/m.sup.2; mass loss rate in g/sec.

(22) The results for ignition time are displayed in FIG. 1. It can be seen that adding ionomers Priex 12031 and 30101 to resin R10 brought a significant improvement in ignition time even for a part which had a smaller wall thickness than that produced with resin R10 (4 mm versus 7 and 11 mm respectively).

(23) Rotomoulded fuel tanks are typically used in boat applications that must fulfil ISO standard 10088. Prior art resin R10 needs a wall thickness of 11 mm to pass the test whereas cross-linked resin R12 needs a wall thickness of 8 to 9 mm. It was surprisingly observed that the blend R6, used in the present invention, that was prepared from resin R10 and a blend of ionomers, was very close to the fire performance of cross-linked resin R12.

(24) Processability.

(25) A two-layer article was produced with resin R9 according to the present invention as outside layer and R11 as inside layer in order to assess the processability. For comparison, another two-layer article was prepared with resin R4 as outside layer and R11 as inside layer.

(26) The results are presented in FIGS. 2 and 3 for the articles prepared respectively with resins R9/R11 and with resins R4/R11.

(27) It was observed that the resins according to the present invention showed a neat interface between the two layers whereas the prior art article had several air bubbles trapped between the two layers especially in the sharp angles.

(28) Delamination.

(29) Rotomoulded articles were prepared with R11 as inside layer and one of R1 to R9 as outside layer.

(30) The linear force in delamination mode was tested with the dynamometer 400/M, Captor 100N testing system. The testing speed was of 50 mm/min, the temperature of 23° C.+ or −2° C. and the force per length was determined in N/cm. The results are displayed in FIG. 4. It was further observed that for the bi-layer structure R8/R11, adhesion between the PE and PA layers was so strong that delamination occurred within the PE layer and not at the interface between the two layers.

(31) Surprisingly, the adhesion level of blends R8 and R9 according to the present invention was higher than that of the starting resins R6 and R7 to which was added a plain polyethylene resin R10 that had no adhesion properties. One would have expected on the contrary, a degradation of the adhesion level of resin R6 or R7 by addition of resin R10.

(32) Additional adhesion tests were carried out on two-layer rotomoulded fuel tanks wherein the external layer had a thickness of 4 mm and was prepared with resin R5 either alone or dry blended in a 50/50 composition with metallocene-prepared polyethylene R10. The internal layer had a thickness of 2 mm and was prepared with polyamide PA11. The rotomoulded parts were cooled with water.

(33) Samples were cut from rotomoulded parts and were immersed in fuel C and in fuel C10 at a temperature of 40° C. Peeling tests were carried out after 1, 2, 3, and 6 months of fuel contact. The results are displayed in Table II.

(34) TABLE-US-00002 TABLE II Resin 0 days 1 month 2 months 3 months 6 months Contact with fuel C R5 19 19 21 18 19 R5 + R10 19 19 17 18 17 Contact with fuel C10 R5 + R10 19 18

(35) These results revealed that the adhesion level was not affected by prolonged contact with fuel, the variations observed being within the limit of accuracy of the method. The same results were observed for structures prepared with the polyamide layer outside and the polyethylene-based layer inside. The adhesion properties were thus preserved making these rotomoulded articles quite suitable for fuel tank applications.

(36) Surface Energy.

(37) In some instances, it is desirable to paint the rotomoulded part. The paintability is function of the surface energy level that must have a value of at least 39 mJ/m.sup.2 in order retain non-polar adhesive systems.

(38) The surface energy was evaluated by a method based on the equilibrium existing between a drop of liquid deposited on a solid surface in the presence of the liquid vapour. The surface energy can be expressed as
γsv=γsL+γL.Math.cos θ
wherein γsv is the surface energy of the solid in the presence of the liquid vapour, γsL is the interfacial energy between solid and liquid, γL is the liquid surface tension and θ is the contact angle of the liquid on the solid. The method is fully described in Dalet (Thèse de Pierre Dalet: intitulée <<Contribution à la corrélation entre architectures macromoléculaires, énergies libres de surface et adhésivité.>> presented in 1999 at Université de Bordeaux-1 and written in collaboration with Prof. J-J. Villenave).

(39) The results for surface energy are presented in FIG. 5. It can be seen that resins R6 and R7 have a surface energy well above the paintability threshold.

(40) Impact Properties.

(41) Two-layer rotomoulded fuel tanks were prepared. The external layer had a thickness of 4 mm and was prepared with resin R5. The internal layer had a thickness of 2 mm and was prepared with polyamide PA11. The impact properties were measured following the method of standard test ISO 6602. The energy curve is displayed in FIG. 6(a) representing the displacement expressed in mm as a function of load expressed in Newtons. They exhibit a completely ductile behaviour quite comparable to that of crossed-linked polyethylene from Paxxon also represented in FIG. 6(b) for comparison.

(42) Permeability.

(43) Permeation tests were carried out at a temperature of 40° C. for fuel C and for fuel C10 using the method of standard test ECE34. In the U.S.A. permeation level for fuel tanks must meet the level required by CARB and EPA of less than 1.5 g/m.sup.2/day, at a temperature of 40° C. for fuel C, and at a temperature of 28° C. for fuel C10. For the fuel tanks prepared according to the present invention, that target was reached respectively for a wall thickness of 10 to 11 mm for fuel C and for a wall thickness of 8 mm for fuel C10. 10 L bottles of different wall thickness were prepared from resin R10 alone or from a 50/50 blend of resin R10 and R5: they were filled respectively with fuel C and with fuel C10. The permeation rate results expressed in g/m.sup.2/day are displayed in Table III.

(44) TABLE-US-00003 TABLE III Thickness R10 R5 + R10 mm Fuel C Fuel C10 Fuel C Fuel C10 6 6.47 7.22 7.37 5.09 8 5.07 4.79 4.33 2.59 10 3.06 2.38 2.19 1.3 12 1.545 2.77 0.76 0.36

(45) The fuel tanks prepared according to the present invention thus have much better barrier properties to fuel than mPE and very good barrier properties to alcohol.

(46) The blend according to the present invention also has the advantage of reducing the cost of layer A as a substantial fraction of the layer may be provided by a low cost resin.

(47) It further offers the flexibility to tailor the blend according to the needs by dry blending the polyethylene composition with another resin selected for example from polyethylene, polypropylene, polyamide, plastomers, polivinylidene fluoride (PVDF) and by modifying the amount of each component to improve either impact or fire resistance or rigidity, or paintability.

(48) The high temperature Audi cycle test was carried out on two layer rotomoulded parts wherein the external layer was prepared from resin R5 and had a wall thickness of 4 mm and the internal layer was prepared from PA11 and had a wall thickness of 2 mm. They passed the test for high temperature alcohol, gasoline, diesel and biodiesel.

(49) Recycled multilayer rotomoulded articles were also tested for impact, tensile properties and permeability. Rotomoulded bilayer fuel tanks prepared from resin R5 and PA11 were ground and re-extruded with 40 wt % based on the total weight of a composition comprising 95 wt % based on the weight of the composition of metallocene prepared polyethylene R10 and 5 wt % of Priex 12301. This compound was ground and used to produce single layer rotomoulded parts.

(50) The processability was excellent.

(51) The impact properties were measured following the method of standard test ISO 6602-3. The tests were carried out at temperatures of 23° C. and of −20° C. on 6 mm thick mouldings.

(52) The results were as follows. Temperature of 23° C. Peak energy=25 J Total energy=48.4 J Ductility index=48% Temperature of −20° C. Peak energy=32.4 J Total energy=56.9 J Ductility index=43%

(53) A ductility index larger than 40% is representative of a ductile behaviour. The samples thus had a ductile behaviour even at low temperature.

(54) Tensile tests were carried out on the same samples following the method of standard test ASTM D693. The results were as follows. Young modulus=591 MPa Yield stress=18.15 MPa Yield elongation=11.4% Rupture elongation=362%

(55) Recycled material can thus be used to produce excellent quality rotomoulded parts such as fuel tanks or tanks.