WO1998003586A1

WO1998003586A1 - Polymer blend

Info

Publication number: WO1998003586A1
Application number: PCT/AU1997/000460
Authority: WO
Inventors: Ru Yu Wu; Lawrence David Mccarthy
Original assignee: Crc For Polymers Pty. Ltd.
Priority date: 1996-07-22
Filing date: 1997-07-21
Publication date: 1998-01-29
Also published as: AUPO116296A0

Abstract

A polymer blend comprising at least one thermoplastic polymer, cellulosic material and at least one polyisobutylene polymer. The cellulosic material for use in the polymer blend may advantageously be recycled newsprint. Polyisobutylenes are often incorporated into thermoplastic polymers such as polyethelene in the manufacture of stretch or cling wrap films. The blending or recycled newsprint with recycled stretch or cling wrap film produces a useful material from waste products. Advantageously the incorporation of cellulosic material and thermoplastic polymers with polyisobutylene polymers also results in improved dispersion and improved wetting with respect to the cellulosic materials with corresponding improvments in mechanical properties.

Description

POLYMER BLEND

The present invention relates to a fibre reinforced polymer and to a process for the production of a fibre reinforced polymer. In particular, the present invention relates to a thermoplastic polymer incorporating cellulosic fibres and to a process for the manufacture thereof. The present invention may find particular application in the recycling and/or reusing of spent materials such as waste paper and waste thermoplastics.

Thermoplastic polymers have, in general, a low elastic modulus. It is well known that the elastic modulus of a polymer may be increased by the addition of fibrous reinforcing agents and/or inert fillers. The resulting polymer composites are generally more rigid and have reduced materials costs since the cost of fibrous reinforcing agents may be significantly less than the cost of the base polymer. Mineral fillers and glass fibres may be used to increase modulus, however, these "hard" fillers generally result in extruder wear and weight increase in the composite. While cellulosic materials such as wood flour and paper pulp have been used in thermosetting molding compounds in order to provide low density, high modulus and high strength, the use of cellulosic materials in thermoplastic polymers has been limited.

This is primarily due to compatibility problems between hydrophilic cellulosic materials and the hydrophobic thermoplastic which results in poor and uneven dispersion. While compounders of thermoplastics have been able to incorporate wood flour in thermoplastic polymers, such as polypropylene, the process requires a high degree of mixing, such as with twin screw extruders, in order to obtain an acceptable blend. However, the wood flour generally remains poorly dispersed.

The incorporation of discontinuous bulky cellulose fibres into polymers is not as facile as mixing wood flour and polymers. Waste paper is a potentially inexpensive source of cellulosic fibres. Fibres from waste paper are tangled and it is not easy to disperse them. Waste paper may also be hammer milled into bulky fibre form but feeding the bulky fibres into extruder is very difficult. Paper granules can be made from hammer milled fibres for the ease of feeding. Irrespective of the form of cellulosic fibres, intensive and prolonged mixing is usually required to impregnate and disperse the fibres. We have found that batch type mixers are usually required for prolonged mixing which is not economical both in terms of energy consumption and man-power. Prolonged mixing also results in extensive breakage of fibres, reducing their effectiveness as reinforcing agents.

Hamed, US. patent 3,943,079 (1976) describes generally the pre-treatment of cellulose fibres with polymer processing lubricants to reduce friction between fibres and thus to improve impregnation and to decrease mixing time.

It is desirable for cellulosic particles to be incorporated into thermoplastic polymers whereby the cellulosic particles are evenly dispersed throughout the thermoplastic polymer and that the thermoplastic polymer wets the cellulosic particles. The degree of dispersion of the cellulosic particles as well as the degree of wetting determines the mechanical properties of the composite materials. We have now found that the incorporation of cellulosic particles into thermoplastic polymers is substantially improved by the addition of polyisobutylene polymers. The term "polyisobutylene polymers" includes homopolymers and copolymers of isobutylene such as the range of homopolymers known as polyisobutylenes and the range of copolymers known as polybutenes. Polybutenes are copolymers of isobutylene and at least one of the n-butenes. Polyisobutylene polymers are generally known as tackifiers and have been used for hot melt adhesives, pressure-sensitive adhesives, stretch and cling films. We have found that these tackifiers provide improved dispersion and wetting and result in composites having improved mechanical properties.

Accordingly there is provided a polymer blend comprising at least one thermoplastic polymer, cellulosic material and at least one polyisobutylene polymer.

The thermoplastic polymer used in the polymer blend of the present invention may be any thermoplastic polymer which may be processed below the thermal decomposition temperature of the cellulosic material (about 200° C). It is preferable that the thermoplastic polymer not be sensitive to water vapour at the processing temperature. The thermoplastic polymer may be in the form of a blend of one or more thermoplastic polymers. Thermoplastic polymers suitable for use in the polymer blends of the present invention include polymers and copolymers of ethylene, modified polyethylene, propylene, styrene, vinyl chloride and other polyolefins. It will be understood by those skilled in the art that the term 'copolymers' includes polymers formed from two or more monomers. Copolymers formed from three monomers for instance, often referred to as terpolymers, are included within the meaning of the term 'copolymer' .

Polyethylene suitable for use in the process of the present invention may include very low, low, linear low, medium and high density polyethylene. Modified polyethylenes have hydrogens on a tertiary C-atom substituted by other groups, such as cross-linked, chlorinated, sulfonated, and chlorosulfonated polyethylenes. Ethylene copolymers suitable for use in the present invention include ethylene/vinyl acetate copolymers, ethylene/vinyl alcohol copolymers, ethylene/ethyl acrylate copolymers and ethylene/methacrylate copolymers. Other polyethylenes suitable for use in the process of present invention include ionomers. lonomers such as those copolymers of ethylene and acrylic or methacrylic acids, which have been neutralised wid metal ions such as sodium, lithium or zinc, are exemplified by the commercial products "Surlyn" (manufactured by Du Pont).

Polypropylene suitable for use in the process of the present invention may include isotactic polypropylene, syndiotactic polypropylene, functionalised polypropylene and modified polypropylene. Modified polypropylene includes block copolymers with ethylene, but-1-ene and higher α-olefin; ethylene / propylene (diene) copolymers, polypropylene / ethylene propylene blends. Functionalised polypropylene includes maleic anhydride grafted polypropylene.

Advantageously, the polymers which may be used in the present invention can be derived from waste plastics materials, especially co-mingled plastics wastes such as multi- layered films and bottles, polymer blends, car bumpers, shrink, stretch and cling films; or contaminated plastics, such as waste detergent, engine oil and edible oil containers, printed botdes and films, agriculture films contaminated with soil or dirt etc. Waste stretch or cling films may be advantageously incorporated into the polymer blend as these waste materials incorporate polyisobutylene polymers.

Cellulosic materials may conveniently be derived from finely ground products of wood pulp, agricultural products such as the shells of peanuts or walnuts, corn cobs, rice hulls, vegetable fibres, bamboo, cotton, hemp or fibres from fruit and vegetable skins such as pineapple and banana skins. It is preferred that cellulosic material be in the form of fibres as fibres present considerable advantages in the reinforcement of thermoplastic polymers.

A particularly convenient source of cellulosic fibres is waste paper and/or newsprint. Waste paper, newsprint and die like typically contain lignin or other incidental components such as dyes, printing pigments, printing binders, trace oils etc. While the properties of the polymer blend may be improved by removing one or more of these incidental components we have found that it is unnecessary as acceptable properties may be obtained in the polymer blend notwithstanding presence of these incidental components. It is preferred that the cellulosic material is either milled or beaten in order to promote particle or fibre separation. Pretreatment of the cellulosic materials is preferred although not necessary to produce acceptable materials. Cellulosic materials may be thermally pretreated immediately prior to blending to improve their compatibility with the thermoplastic polymer thereby further reducing die compounding time required to produce a homogeneous polymer blend.

Thermal pretreatment of the cellulosic materials is performed by heating to temperature which results in dehydration without destruction of the particles. Hammer milled newspaper fibre heated to temperatures between 80 and 200°C in an inert atmosphere results in dehydration without significant destruction of the fibre. It is believed that this dehydration of die fibres renders die fibres less hydrophilic and more susceptible to polymer adsorption. We have found tiiat such thermal treatment results in increased homogenity in the polymer blend. While a degree of dehydration will occur during the compounding of the fibres into the polymer blend, the compounding times are reduced by the use of thermal pretreatments which it is believed to be as a result of the partial dehydration of the cellulose.

The cellulosic particles may be heated in an oven under an oxygen depleted atmosphere at a temperature approaching the decomposition temperature of the cellulose. If oxygen is present, present rapid decomposition of the paper occurs at this temperature and any fibrous structure may be lost. For example, when using hammer milled newsprint, heating in the range of from 80 to 200°C for 20 minutes under forced nitrogen was found to be advantageous. Other fibrous cellulosic materials which contain water may also be pretreated at temperatures dependant on die impurity content, chain length and cellulose chemistry.

The polymer blends of d e present invention may incorporate cellulosic materials in amounts from 1 to 99% by weight of the polymer blend, preferably in the range of from 5 to 75 % by weight of the polymer blend.

At least one polyisobutylene polymer may be a polyisobutylene homopolymer or a polyisobutylene copolymer or a mixture thereof.

Polyisobutylene homopolymers range from low molecular weight semi-liquids to high molecular weight elastomers.

Polyisobutylene copolymers are generally obtained from a mixture of C„H₈ isomers in the form of the C₄ fraction of processes that crack petroleum fractions and natural gas. The four C H₈ isomers are 1-butene, cis-2-butene, trans-2-butene and isobutylene. Copolymers of these C H_g isomers are useful polyisobutylene copolymers. Other comonomers such as isoprene may be used in the polyisobutylene copolymers.

It is preferred mat the polyisobutylene homopolymers and copolymers have a low molecular weight form of a highly viscous liquid. Polyisobutylene polymers having a molecular weight average of from 200 to 10,000 are particularly suitable, preferably polyisobutylene has a weight average molecular weight from 300 to 10,000 and most preferable a weight average molecular weight of about 1500.

We have observed that polyisobutylene assists the dispersion of cellulosic materials and improves their adhesion to the thermoplastic polymer.

Tackifiers used for stretch or cling wrap applications, such as low molecular weight polyisobutylene polymer may advantageously be used. It is particularly convenient for the polyisobutylene polymer to be provided in die form of recycled stretch or cling wrap whereby die thermoplastic polymer or polymers also present in the recycled material may be incorporated into die polymer blend of the present invention.

It is preferred mat die polyisobutylene polymer be present in the polymer blend in an amount of from 0.1 to 10% by weight of the polymer blend, dependent upon the amount of cellulosic material. The process may be applied to recycled materials such as polymer films including shrink wrap and which hitherto have presented an environmental problem in tiiat applications for the recycled materials have not been available.

The polymer blend of d e present invention may also incorporate various other additives typical of those incorporated into thermoplastic blends. Such additives may include pigment, colorants, antioxidants, UV stabilizers, plasticisers, lubricants, flame retardants, nucleating agents, powdery and fibrous fillers and chemical blowing agents.

We have found tiiat the use of a polyisobutylene polymer improves homogeneity, reduces processing times, improves some mechanical properties and improves the appearance of articles manufactured from the polymer blend.

In accordance with a second aspect of the present invention, there is provided a process for die production of a polymer blend comprising mixing cellulosic material witii at least one polyisobutylene polymer and at least one tiiermoplastic polymer. We have found that it is preferable for the polyisobutylene polymer to be blended with at least a portion of the thermoplastic polymer prior to the incorporation of the cellulosic material into the blend.

The compounding of the polymer blend can be done on conventional polymer processing mixers or by any mixer capable of compounding highly viscous polymeric systems at elevated temperatures. Continuous mixing equipment may also be used. Preferably a twin screw extruder is used to blend d e components of the polymer blend. Solvents or heat may be used to aid adsorption. Typically die mixer is heated to a suitable temperature and the required amount of polymer is added. After the polymer is completely molten the polyisobutylene polymer is added. The cellulosic materials are added as rapidly as possible, keeping torque below the equipment maximum. It is conventional to allow mixing for a fixed time or until die torque has dropped to a prescribed minimum.

It is preferred tiiat the process of the present invention incorporates a pre-treatment step whereby die cellulosic material is treated by heating to a temperature which results in the dehydration of the cellulosic material without the destruction of the particles or fibre. For example, hammer milled newspaper fibre may be treated at temperatures between 80 and

200° C in order to result in dehydration widiout significant destruction of the fibre.

The polymer blend may be removed from d e blender, divided into smaller pieces and allowed to cool. These pieces may then be taken and platten press molded into plaques and bars. Alternately the material could be taken directly from die mixer and moulded while hot. Certain compositions within the scope of the invention have low enough viscosity to be further processed by extrusion or injection molding vastly extending d e possible applications.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers. The following examples illustrate certain embodiments of the invention but are not meant to limit the scope of the invention in any way.

EXAMPLE 1 5 Hammer milled newsprint was dried for 8 hours at 90°C under a forced draught of nitrogen. During tiύs time the paper released approximately 10 % W/W of water. 98.6 gram of stretch wrap waste (comprising 5 % W W of polyisobutylene in linear low density polyethylene) was softened at 200°C (5 minutes) in a 242 cc batch mixer attached to a Brabender PL2000 unit. 239.3 gram (70% W W) of die dried newsprint was mixed in as quickly as possible (approx. 10 20 minutes). Maximum torque was 7,000 m-gram and final torque was 3,400 m-gram. The resulting composite was a homogeneous plastic mass with a dark grey colouration.

.An 8cm x 8cm x 0.43 cm plaque was pressed at 79.4 kg/cm² and 200°C. The specific gravity of the plaque was 1.27. Flexural tests were performed on samples cut from the plaque. The 15 flexural modulus was found to be 1997 Mpa. Breaking stress was found to be 30 Mpa, breaking strain was found to be 0.034 mm/mm.

COMPARATIVE EXAMPLE 2

Anotiier composite material was prepared according to the method of example 1 , with the 20 substitution of pure LLDPE for stretch wrap waste.

The time required to add the dry newsprint was 34 minutes (an increase of 14 minutes over Example 1). The maximum torque in the mixer was 8,600 m-gram and the final torque was 4,600 m-gram (compared to 7,000 m-gram and 3,400 m-gram in Example 1). 25

Breaking stress was found to be 25 MPa, breaking strain was found to be 0.015 mm/mm and flex modulus was found to be 2,627 MPa.

EXAMPLE 3 AND COMPARATIVE EXAMPLES 4 TO 10 30 Various of potential processing aids were assessed by judging tiieir efficiency in impregnating and dispersing cellulosic fibres and compared witii comparative example 2 which had no additives. The efficiency of impregnation of the fibres can be reflected by the ease of incorporation of d e fibres. The total mixing time served as a quantitative indicator of wetting. The total mixing time is the time taken to feed all the fibres into Brabender mixer as fast as one can and until the extruder torque becomes stable.

The dispersion of fibres was easily assessed visually during mixing by observing how much undispersed fibre aggregates were present. Table 1 is a summary of findings:

TABLE 1

sample Processing aid Dispersion Wetting

2 none 0 0

3 Polyisobutylene (Ultravis) +3 +2

4 Glycerol mono-oleate 0 +3

5 Waste engine oil -1 + 1

6 Ethylene vinyl alcohol + 1 +2

7 Hot melt adhesive 0 0

8 Chlorinated paraffin oil -1 0

9 Metallocene polyetiiylene + 1 + 1

10 Polyterpene -1 -1

In Table 1, 0 means no effect, + 1 means noticeable improvement, +2 means moderate improvement, +3 means substantial improvement and minus sign means negative effect. COMPARATIVE EXAMPLE 11

50% paper granules (from ground up telephone books with a small amount of starch binder) and 50% LLDPE were mixed on a Windsor co-rotating intermeshing twin screw extruder. The diameter of the screw was 65 mm and die length to diameter ratio was 8: 1. The paper granules were used as obtained with no additional drying. The barrel was kept at 180°C. During extrusion, die stabilised electrical current consumption was 2.8 Ampere. The extrudate passed through 4.5mm holes to produce a rod. There was considerable breakage of the rod during extrusion and the extrudate could be collected with bare hands due to d e protrusion of uncombined paper.

After compounding and extrusion the rods were pelletised and 8cm x 8cm x 0.3 cm plaques were pressed at 79.4 kg/cm and 190^*C. Flexural modulus was found to be 618 Mpa. Strain at break was found to be 1.8% and die flexural strength was found to be 6.6 Mpa. The high speed puncture impact strength was 3.2 Joule.

EXAMPLE 12

A composite material was prepared according to d e method of Example 11 , with the addition of 5% polyisobutylene Ultravis (BP Chemicals) as used to produce stretch wrap. The electrical current reading was 2.0 Ampere for stable extrusion. Extrudate breakages was significantly less than in example 11. The improved incorporation of the paper in the plastic meant mat the extrudate could no longer be handled by bare hands as in example 11 , the molten plastic made up d e majority of the extrudate surface.

Flexural modulus was found to be 471 Mpa. Strain at break was found to be 2.7% and the flexural strength was found to be 7.4 Mpa. The high speed puncture impact strength was 5.9 Joule.

EXAMPLE 13

Approximately 2 g samples of the extrudate pellets from Examples 11 and 12 were extracted in a soxhlet apparatus for 8 hours using xylene solvent. This completely removed all of the LLDPE from the composite and left the fibre mass for examination. The fibre mass from example 11 had not significantly changed from its original granular form. The fibre mass from Example 12 was virtually completely disaggregated leaving very few residual granules showing tiiat the presence of the polyisobutylene polymer had resulted in good dispersion of die cellulose fibre. See Figure 1.

COMPARATIVE EXAMPLE 14

Car interior boards made of 50% polypropylene, 45% wood flour and 5 % talc were cut into small pieces and fed into a Brabender 242 cc batch mixer and mixed at 190° C for two minutes.

An 8 cm x 0.45 cm plaque was pressed at 79.4 kg/cm² and 190°C. Wood flour agglomerates could be easily seen with the naked eye from die surface of the plaque.

EXAMPLE 15

Another composite material was prepared according to die method of example 14 with the addition of 2% w/w of polyisobutylene (Ultravis) also included in the Brabender mixture.

The resulting compression moulded plaque looked very homogenous and wood flour aggregates could not be detected.

EXAMPLE 16-18

Low melt flow index polypropylene (PP) and talc were mixed in a Brabender mixer at 190°C and ti en granulated paper was added to d e mixer. Mixing was allowed to continue until all die paper was added plus 2 minutes. The percentages of constituent materials of EXAMPLE 16-18 are listed in Table 2.

Plaques were pressed at 80 kg/cm² and 190°C from the above mixed materials. Impact resistance of the plaques were evaluated by using ICI Instrumented Impact Tester. Mechanical properties were also evaluated by tiiree point bend flexual test. The results are shown in Table 2.

TABLE 2

Example Paper PP PIB Talc Impact Modulus Strength Break

% % % % (Joule) (MPa) (MPa) Strain %

16 20 73 2 5 1.8 1556 23.12 2.76

17 35 57.5 2.5 5 2.3 1845 24.59 2.93

18 45 47.5 2.5 5 2.4 2620 26.88 2.11

Claims

CLAIMS:

1. A polymer blend comprising at least one thermoplastic polymer, cellulosic material and at least one polyisobutylene polymer.

2. A polymer blend according to claim 1 wherein said thermoplastic polymer is selected from the group consisting of polymers, and copolymers of ethylene, propylene, styrene, vinyl chloride and derivatives thereof.

3. A polymer blend according to claim 2 wherein the polymers and the copolymers of ethylene are selected from the group consisting of: very low, low, linear low, medium and high density polyetiiylene; modified polyetiiylenes having substituents at the tertiary C- atom; ethylene copolymerised with vinyl acetate, vinyl alcohol, ethylacrylate and methacrylate; and polyethylene ionomers.

4. A polymer blend according to claim 2 wherein the polymers and copolymers of polypropylene are selected from the group consisting of: isotactic polypropylene, syndiotactic polypropylene, functionalised polypropylene including maleic anhydride grafted polypropylene and modified polypropylene including block copolymers with etiiylene, but-1-ene and higher α-olefin; ethylene / propylene (diene) copolymers, polypropylene / etiiylene propylene blends.

5. A polymer blend according to any one of claims 1 to 5 wherein d e thermoplastic polymer is derived from waste plastics materials.

6. A polymer blend according to claim 5 wherein said waste plastics materials are selected from the group consisting of co-mingled plastics wastes incorporating at least one of multi-layered films and bottles, polymer blends, car bumpers, shrink, stretch and cling films; contaminated plastics, including waste detergent, engine oil and edible oil containers, printed bottles and films, agriculture films contaminated with soil or dirt.

7. A polymer blend according to any one of claims 1 to 6 wherein the cellulosic material is selected from the group consisting of finely ground products of wood pulp, the shells of

5 peanuts or walnuts, corn cobs, rice hulls, vegetable fibres, bamboo, cotton, hemp or fibres from pineapple and banana skins.

8. A polymer blend according to any one of claims 1 to 7 wherein the cellulosic material is in the form of waste paper or newsprint.

10

9. A polymer blend according to claim 8 wherein die cellulosic material has been thermally pretreated prior to blending widi the thermoplastic polymer and die polyisobutylene polymer.

15 10. A polymer blend according to any one of claims 1 to 9 wherein the at least one polyisobutylene polymer is selected from the group consisting of polyisobutylene homopolymers, polyisobutylene copolymers and mixtures thereof.

11. A polymer blend according to any one of claims 1 to 10 wherein the at least one 20 polyisobutylene polymer comprises a polyisobutylene copolymer.

12. A polymer blend according to claim 11 wherein the polyisobutylene copolymers is a copolymer of isobutylene and at least one comonomer selected from die group consisting of 1-butene, cis-2-butene and trans-2-butene.

25

13. A polymer blend according to any one of claims 1 to 12 wherein the weight average molecular weight of the at least one polyisobutylene polymer is in the range of from 300 to 10000.

14. A polymer blend according to any one of claims 1 to 13 wherein the weight average molecular weight of the at least one polyisobutylene polymer is about 1500.

15. A process for the production of a polymer blend comprising blending cellulosic material with at least one thermoplastic polymer and at least one polyisobutylene polymer.

16. A process according to claim 15 wherein the process further comprises forming a pre- blend of at least one thermoplastic polymer and at least one polyisobutylene polymer prior to blending the cellulosic material into die pre-blend.

17. A process according to either claim 15 or claim 16 wherein the blending of die cellulosic material with die at least one thermoplastic polymer and at least one polyisobutylene polymer is performed in either a batch mixer capable of compounding highly viscous polymeric systems at elevated temperatures or continuously mixing extruders.

18. A process according to claim 17 wherein the blending is preformed in a twin screw extruder.

19. A process according to any one of claims 15 to 19 wherein the process further comprises the step of thermally treating the cellulosic material prior to blending die thermally treated cellulosic material with the at least one thermoplastic polymer and the at least one polyisobutylene polymer wherein said step of tiiermally treating the cellulosic material is conducted at a temperature in the range of from 80°C to 200°C under an inert atmosphere.