Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L7/00—Compositions of natural rubber
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L75/00—Compositions of polyureas or polyurethanes; Compositions of derivatives of such polymers
  • C08L75/04—Polyurethanes
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L77/00—Compositions of polyamides obtained by reactions forming a carboxylic amide link in the main chain; Compositions of derivatives of such polymers
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L9/00—Compositions of homopolymers or copolymers of conjugated diene hydrocarbons
  • C08L9/02—Copolymers with acrylonitrile
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08C—TREATMENT OR CHEMICAL MODIFICATION OF RUBBERS
  • C08C19/00—Chemical modification of rubber
  • C08C19/04—Oxidation
  • C08C19/06—Epoxidation
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L15/00—Compositions of rubber derivatives
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L23/00—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers
  • C08L23/02—Compositions of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Compositions of derivatives of such polymers not modified by chemical after-treatment
  • C08L23/04—Homopolymers or copolymers of ethene
  • C08L23/08—Copolymers of ethene
  • C08L23/0846—Copolymers of ethene with unsaturated hydrocarbons containing other atoms than carbon or hydrogen atoms
  • C08L23/0869—Acids or derivatives thereof

Definitions

• the present invention is directed to a rubber matrix composition including natural rubber with the capacity to form a thermoplastic composite with a range of thermoplastics.
• Natural rubber has been used for a variety of purposes over time however, there are some properties which make rubber more difficult to use in industrial processes and/or make it unsuitable for certain applications. These properties include having a high molecular weight, high viscosity, often being contaminated with naturally occurring proteins and often having a high dirt content. Additionally rubber as it is generally used is cross linked by vulcanisation. These cross-links are difficult to reverse and as a consequence recycling of used rubber products is difficult to satisfactorily achieve.
• Natural rubber also has some very desirable properties compared to plastics and some other rubbers which properties include, toughness, dynamic sealing properties, resilience, flex fatigue life, low compression and tension set, and low flex modulus and creep. There has been a desire therefore to blend natural rubber and certain thermoplastics to make a composite having the desirable properties of rubber but processable and reprocessable as thermoplastics.
• Blends between thermoplastics and natural or synthetic rubbers have been facilitated in the past in a number of ways by introducing polar compounds into the natural or synthetic rubber and one such approach has been to introduce acrylonitrile into natural rubbers and synthetic rubbers to facilitate such a blending.
• one or more first compatabilisers selected from a group of polymers containing either i) a nitrile group, ii) a halogen, iii) an acetate group, iv) an epoxide, v) a styrene, or vi) an acrylate
• one or more second compatabilisers which are interfacial copromoters selected from a group comprising either i) polyvinyl acetate, ii) ethylene vinyl acetate, iii) polyacrylonitrile or high nitrile resin, iv) acrylamide or polyacrylamide, v) a phenolic resin, vi) an acrylate polymer, vii) a halogenated polymer, viii) maleic anhydride or polymaleic anhydride, or ix) a bismaleimide.
• interfacial copromoters selected from a group comprising either i) polyvinyl acetate, ii) ethylene vinyl acetate, iii) polyacrylonitrile or high nitrile resin, iv) acrylamide or polyacrylamide, v) a phenolic resin, vi) an acrylate polymer, vii) a halogenated polymer, viii) maleic anhydride or polymaleic anhydr
• the rubber matrix may be mixed with a range of thermoplastics to form thermoplastic rubber composites.
• the thermoplastic may be selected from one or more of the group including, but not limited to polyolefins, polyamides, polyesters, polyurethanes, polystyrene, acrylonitrile butadiene styrene, all of which will be described in detail later.
• the first and second compatabilisers are different.
• thermoplastics are recyclable and/or reprocessable and can be re-moulded.
• thermoplastic rubber composite formed by mixing the rubber matrix of the present invention with a thermoplastic can similarly be recycled, reprocessed, and/or re-moulded.
• the natural rubber is preferably selected from the grades known as deproteinated natural rubber (DP-NR), oil extended natural rubber (OE-NR), peptised natural rubber, superior processing rubber (SP or PA), standard Malaysian rubber (SMR) constant viscosity (SMR-CV), low viscosity (SMR-LV), or general purpose (SMR-GP) grades or ISNR LCV grades. These grades tend to have a low protein and low dirt content. Most preferably SMR or ISNR LCV grades are used.
• the content of natural rubber in the rubber matrix may be between 10 phr and 90 phr (parts per hundred rubber).
• the rubber matrix has between 35 phr to 40 phr natural rubber for the desirable elastoplastic properties of the natural rubber to be transferred to a final product. If less than 10 phr of natural rubber is used in the rubber matrix the desirable properties of natural rubber tend not to be inherent in the final product.
• the molecular weight of natural rubber is high and it is a highly viscous and resilient rubber.
• the normal process involved with blending natural rubber with plastics is to break down the molecular weight of natural rubber so as to match it with the size of the plastic in order to get effective blending.
• the present invention is believed to work at least in part by preventing the natural rubber, which is a highly resilient material and normally regains its molecular weight, from creating a discontinuous phase between the blending plastic and that of the natural rubber. In the present case it is thought that this problem is overcome by the addition of a polar rubber which also has a lower molecular weight and creates a better base and a better match between the rubber and the plastic phases.
• the lower molecular weight is thought to reduce and stabilise the viscocity of the rubber phase, which in turn increases the flow characteristics.
• the polar compounds also are also thought to increase the attractive forces between the plastics and rubber phases.
• the polar groups increase the resistance of natural rubber to oils and polar petrochemical based fluids.
• thermoplastic compositions each having different properties may be formed.
• the properties may be tailored to suit a particular application.
• a range of soft composites may be formed by compounding the rubber matrix with polyolefins, polyvinyls or polyurethanes for example.
• intermediate composites may be produced by compounding the rubber matrix with polyurethanes, polyamides, polyvinyls or polyesters for example.
• Rigid composites may be produced by compounding the rubber matrix with polyolefins, polyurethanes or polyamides for example.
• the natural rubber content in the rubber matrix is preferably about 20-70% and most preferably about 40%, with the rubber matrix and plastics preferably being blended in relative proportions of 5-70 parts to 95-30 parts to a total of 100 parts respectively.
• the rubber matrix comprises more than 75 parts per hundred of the total composite the flow of the composite will be restricted and a continuous phase may not form in the composite.
• the plastics in such soft composites might be selected from the group comprising polypropylene, polyethylene, polyvinyl acetate, ethylene vinyl acetate, ethylene propylene plastic (Engage; DuPont), polyurethanes or polyvinyl chloride.
• the first compatabiliser is selected to have good natural rubber blending properties, and also to present a polar group for attraction by the second compatabiliser.
• the first compatabiliser is also thought to stabilise the viscosity of natural rubber. At least some of the properties of the first compatabiliser will be transferred to the final composition, the degree of which will be determined in part by the amount of first compatabiliser in the final composition.
• a nitrile based first compatabiliser may be selected from: an acrylonitrile diene rubber such as nitrile isoprene rubber or nitrile butadiene rubber; nitrile natural rubber; polyacrylonitrile; high nitrile polymer.
• the amount of nitrile based compatabiliser added to the rubber matrix will be determined by the desired properties of the final composition, but is preferably greater than 10% of the rubber matrix.
• the nitrile butadiene, nitrile isoprene and nitrile natural rubber preferably has an acrylonitrile content of over 20%.
• the nitrile content will improve the oil and fuel resistance of the rubber. Further, the elastic behaviour of the nitrile rubbers becomes poorer as the nitrile content increases however at the same time the polymer becomes more thermoplastic which is advantageous regarding the processability of the compounds.
• the compatibility with polar plasticisers or polar plastics improves with increasing nitrile content.
• High nitrile polymers having a nitrile content of more than about 50% may also be used.
• Barex 210 (B-210) (BP America Inc) is a commercially available acrylonitrile-methyl acrylate-butadiene (70:21:9 parts by weight) polymer. These polymers have excellent barrier properties and are useful in packaging solids, liquids and gases of various types.
• a halogenated first compatabiliser may be a halogenated polymer selected from: chlorinated rubber; polyvinyl chloride; polychloroprene (Neoprene; DuPont); vinyl diene fluoride.
• Chlorinated polyethylene or chlorosulphonated polyethylene e.g. Hypalon; DuPont
• the rubber matrix may be halogenated in situ by the addition of a halogen source such as N- bromosuccinimide.
• a further alternative is to introduce halogen into the composition by the inclusion of chlorinated paraffin oil.
• the halogenated compatabiliser is used in conjunction with a nitrile compatabiliser.
• the halogen containing polymer comprises greater than 15% of the rubber matrix.
• a rubber matrix containing a halogen based first compatabiliser will be particularly suited to blending with polyvinyl chloride, polyamides, polyurethanes and/or polyesters.
• An epoxide based first compatabiliser may be an epoxidised natural rubber preferably formed by the reaction of natural rubber with hydrogen peroxide/formic acid/acetic acid.
• the epoxide based compatabiliser has an epoxide content of 20 to 50% to give a rubber matrix having an epoxide content of 10 to 25%.
• An acetate containing first compatabiliser may be selected from: polyvinyl acetate; ethylene-vinyl acetate containing a relatively high vinyl acetate content; a vinyl acetate rubber.
• the acetate polymer comprises 20 to 50% of the rubber matrix and more preferably comprises 30%, and the rubber matrix has a vinyl acetate content of greater than 20%.
• An acrylate based first compatabiliser may be selected from: an acrylic rubber such as Vamac (Dupont), or one formed from the following monomers: ethyl acrylate; methyl acrylate; methyl methacrylate.
• the acrylate compatablilser is used in conjunction with a nitrile compatabiliser in about equal ratios.
• the combination of acrylic and nitrile first compatabilisers is particularly suited to blending with polyamides or acrylates.
• a styrene based first compatabiliser may be selected from: styrene natural rubber; styrene butadiene rubber; styrene isoprene styrene block coploymer (SIS) (e.g. Kraton; Shell); styrene ethyl butylene styrene block copolymer (SEBS).
• SIS styrene ethyl butylene styrene block copolymer
• SEBS styrene ethyl butylene styrene block copolymer
• a rubber matrix containing a styrene based first compatabiliser may be particularly suited to blending with a styrene thermoplastic such as polystyrene or an acrylonitrile butadiene styrene (ABS).
• a combination of more than one of the first compatabilisers may be used in the rubber matrix so as to impart at least some of the characteristics of each of the compatabilisers onto the rubber matrix.
• nitrile rubbers may impart a degree of swell resistance to the rubber matrix such that a final composition may have increased resistance to oils, fuels and fats.
• halogenated rubbers, and in particular chlorinated rubbers are fire resistant and therefore incorporation of them into the rubber matrix will increase the fire resistance as well as the swell resistance of the final product.
• a preferred combination of first compatabilisers is a nitrile rubber and a chlorinated rubber which will tend to increase the resistance of a final composition to fire and to petrochemical based solvents and oils.
• the second compatabiliser is chosen to provide a greater polarity or charge density within the rubber phase of a composite to facilitate blending with thermoplastics that do not readily blend with the first compatabiliser.
• the choice of second compatabiliser is not restricted to those compounds that can interact with the largely non-polar rubber and still present a polar group. They are selected so as to be able to interact with, for example the polar group presented by acrylonitrile, and then present a further polar group with greater polarity or charge density to thereby increase the range of plastics that can be mixed with the rubber matrix. It has been found that in many instances natural rubber is incompatible with, for example, a nitrile rubber-polar thermoplastic blend. However upon addition of a second compatabiliser it is possible to incorporate natural rubber and achieve a continuous phase thermoplastic elastomer composition.
• polyvinyl acetate, ethylvinyl acetate, acrylamide or polyacrylamide, polyacrylonitrile or high nitrile resin, an acrylate polymer, a halogenated polymer, maleic anhydride or polymaleic anhydride, or a bismaleimide is used as a second compatabiliser it is possible to achieve good compounding with the group including but not limited to polyamides, polyurethanes, polyesters, polystyrene including high impact polystyrene, acrylonitrile butadiene styrene, as well as the more readily blended plastics such as the polyolefins.
• aspects of the present invention involve the formation of two phases, a rubber matrix as a rubber phase and a thermoplastics component in a plastics phase, and the invention thus involves a first mixing of components to form the rubber matrix.
• Combining the rubber matrix with the plastics phase involves a second mixing of the rubber matrix (rubber phase) with the plastics phase.
• the rubber matrix is substantially a rubber phase and acts as an intermediate.
• the rubber matrix can be tailored to be combined with any one of a number of different thermoplastics.
• the ratio of rubber phase to plastic phase is between 5:95 and 90:10, however compositions having greater than about 75% rubber phase tend to have a high viscosity and do not flow easily and therefore may be of limited use.
• the composition is required to have a continuous plastic phase and therefore the plastic phase should comprise at least 10% of the final composition. These portions are necessary to provide sufficient rubber to give elastomeric compositions and sufficient plastic to provide thermoplasticity. The ratio of rubber to plastic can be altered within these limits to form a composition having the desired characteristics.
• the rubber phase (or rubber matrix) is formed first and includes the steps of mixing components of the rubber phase including a) the natural rubber; b) a first compatabiliser and, c) a second compatabiliser and d) any further additives that might be required.
• the rubber phase is formed in a cold mixing process. Such a cold mixing process will typically be performed at a temperature of less than about 120°C. The cold mixing is thought to reduce the particle size of the natural rubber to below about 50 ⁇ thus forming an intimate mixture of natural rubber particles dispersed in the rubber matrix. After mixing or masticating the rubber phase is normally viscosity stabilised once it is formed and may be left to mature before inclusion in a second mixing as described below.
• the first compatabiliser apart from providing polarity to the rubber matrix, in particular is thought to stabilise the viscosity of the natural rubber in the matrix and prevent the normal tendency of the rubber to regain its molecular weight thus creating a discontinuity between the plastics phase and the natural rubber.
• the second compatabiliser is then thought to provide further polarity to the matrix so that a range of polar thermoplastics are compatible with the matrix.
• a second mixing may be carried out using any of the known methods such as melt mixing or dynamic vulcanisation.
• Dynamic vulcanisation is preferred and may be carried out using conventional masticating equipment, for example a Banbury mixer, Brabender mixer, mixing extruder or a twin screw extruder.
• the conditions of high shear provided under dynamic vulcanisation conditions provides for dispersal of the rubber phase and plastics phase.
• the thermoplastic composition is formed by mixing the plastics phase and the rubber phase and masticating the mix at a temperature sufficient to at least soften the plastic, but more preferably a temperature above the melting point of the plastic.
• the plastic melts at less than 205°C.
• Representative temperatures may include but are not limited to: for polypropylene 170°C; polyethylene 130-150°C; polyamide 180-200°C; thermoplastic polyurethane 180-200°C; polyester 200°C. It is preferable that the melt temperature of the plastic is less than 205°C because the natural rubber will tend to degrade above this temperature. Heating and masticating at these temperatures is usually sufficient to allow cross link formation.
• compositions of the invention may also be prepared by methods other than dynamic vulcanisation.
• a fully vulcanised rubber phase may be powdered and mixed with the plastics phase and provided that the rubber particles are small and there is sufficient match between the size of the rubber particles and the plastics, a composition having rubber particles well dispersed in the plastics phase can be formed.
• the mixing of the rubber matrix with the plastics phase will require the addition of a curative agent to allow the formation of cross links within the rubber matrix.
• a curative agent to allow the formation of cross links within the rubber matrix.
• certain plastics such as ethylene vinyl acetate or polyethylene are used there may be some cross linking of the plastic with itself and/or with the rubber matrix.
• Any of the curative systems typically used in rubber vulcanisation can be used.
• the curative system may be selected from the group comprising but not limited to: a dimethylol phenol system (e.g.
• the curative agent is a cross linking agent such as a peroxide bismaleimide system.
• the curative may include an interfacial promoter such as for example phenylene bismaleimide (HVA 2 , Dupont), ethylene glycol dimethacrylate (Perkalink 401; Akzo Nobel), trimethylo propane trimethacrylate (Perkalink 400; Akzo Nobel), triallyl isocyanourate (Perkalink 300; Akzo Nobel) or triallyl cyanourate (Perkalink 301; Akzo Nobel).
• the interfacial promoter may also act as stabilisers in an overall peroxide/urethane cross linking system.
• An advantage of a peroxide curative system may be the creation of cross links between the plastic and rubber phases when the peroxide is used in conjunction with SARET/HVA2, and use of a peroxide curative system may lead to a composite having improved tensile strength and improved high temperature strength.
• peroxide curative systems can not be used in direct contact with polypropylene due to the action of peroxide degrading the plastic, however they may be used in a rubber matrix which is subsequently mixed with polypropylene. Further, it may not be possible to use peroxide curing systems with maleic anhydride in an open system due to potential for ignition in contact with air.
• Peroxide curative systems are preferably not used with chloroprene rubbers, in which case magnesium oxide or zinc oxide may be used as curatives preferably in conjunction with phenolic resins.
• the peroxide may be chosen from the group including, but not limited to, dicumyl peroxide, di-tert-butyl peroxide, di (2-tert-butyl peroxy isporopyl) benzene.
• the peroxides may be supported on an inert carrier.
• Peroxide curative systems are less commonly used when the total rubber content in the final composition is less than 15% unless HVA2 or SARET are present. Typically when the total rubber content in the final composition is less than 15%, HVA 2 may provide sufficient cross linking however small amounts of peroxide may be used to assist in the cross linking. If HVA2 or SARET are not present the peroxides are likely to degrade the polypropylene and thus the composition may lose the desirable properties.
• a sulphur based curative system will not create cross links between the plastic and rubber phases and the resultant composition will have a lower compression set and better tensile properties than a composition having the rubber and plastics phases cross linked.
• the curative agents are preferably added to the rubber matrix while masticating, that is at the first mixing stage.
• the rubber matrix content is between 10% and 20% of the total composition the HVA2 should be added to the plastic phase and the peroxide to the rubber phase.
• peroxide should not be used and other curatives such as an accelerated sulphur system or a phenolic system may be used if required.
• thermoplastic rubber composition may be modified by the inclusion of additives which are conventional in the compounding of rubbers and/or thermoplastics.
• additives which might be used could include heat stabilising chemicals, flame retarding chemicals, peptising agents, fillers, extenders, plasticisers, pigments, accelerators, stabilisers, antidegradants such as anti-oxidants and UV filters, processing aids and extender oils.
• halogen containing radicals such as tin chloride or chlorinated paraffin oil are used in a composition
• magnesium oxide or maleic acid may be added to the composition to act as scavengers and/or pH stabilisers.
• Suitable UV filters may be selected from one or more of the group including, but not limited to, Tinuvan P (Ciba Geigy), titanium dioxide or carbon black. Tinuvan P is preferably added according to the manufacturers directions. Titanium dioxide or carbon black are preferably added at about 2.5 parts per hundred parts of the final composition.
• Suitable plasticisers may be selected from one or more of the group including, but not limited to, aromatic, naphthenic and paraffinic extender oils, phthalate plasticisers, sulphonamide plasticisers, adipate plasticisers or phosphate plasticisers.
• Preferred plasticisers are dehydrated castor oil which may be added at 0.8 phr of rubber content, and cumarone and indene resins are ideally suited for the compositions of the present invention at levels up to 5 phr.
• Processing aids may include internal lubricants to increase flow and enhance mixing particularly during the mastication stage.
• Suitable lubricants may include zinc or magnesium salts.
• the lubricant is zinc stearate which is added during mastication.
• the zinc stearate is readily added in the form of zinc oxide (e.g. from about 5 to about 15 phr) plus stearic acid (e.g. from about 1 to about 5 phr).
• the rest of the curing system is ordinarily kept apart from the elastomer until just prior to curing.
• Reinforcing fillers may be selected from the group comprising, but not limited to, carbon black, clays, minerals such as talc and silica. Fillers tend to increase the tensile strength of the final composition. Fillers may be added up to levels of 30phr.
• Polypropylene homopolymer may also be added to balance mould shrinkage caused by the addition of fillers.
• Heat stabilising additives may be selected from the group comprising, but not limited to, phenolic resins (e.g those available from Hylam Bakelite); Flectol H; chlorinated rubbers.
• Suitable antioxidants may be selected from one or more of the group including, but not limited to, Wingstay L/100 (Goodyear); di-naphthyl- -phenylene diamine (Santowhite Cl, Monsanto); styrenated phenol (Montaclere-SE, Monsanto); 2,5-di(tert-amyl) hydroquinone (Santovar-A, Monsanto); 4,4'-butylidenebis-(6-tert-butyl-m-cresol) (Santowhite, Monsanto); tributyl thiourea (Santowhite-TBTU, Monsanto); 6-tert-butyl- m-cresol/sulfur dichloride (Santowhite-MK, Monsanto); trinonyl phenylene phosphate (TNNP; Ciba Geigy).
• antioxidants are added at 1 to 2 % of the total composition.
• Antidegradants that may be added could include ethylene propylene diene terpolymer (EPDM) rubbers. These can be added at 5% of the total composition to improve the weatherability of the composition. Levels over 5% may have an adverse impact on curing because EPDM are slow curing rubbers.
• EPDM ethylene propylene diene terpolymer
• Peptising agents may be selected from any of those known in the art, such as Renacit 1 1 (Bayer). These agents are preferably added at about 0.07 % of the total composition.
• the invention might also be said to reside in a natural rubber thermoplastics composite of a rubber matrix of the first aspect of the invention blended with any one or more of the thermoplastics selected from the group comprising polyolefins, polyurethanes, polyesters, polyamides, acrylates, acrylonitrile butadiene styrene (ABS).
• the thermoplastics selected from the group comprising polyolefins, polyurethanes, polyesters, polyamides, acrylates, acrylonitrile butadiene styrene (ABS).
• first compatabilisers selected from a group of polymers containing either i) a nitrile group, ii) a halogen, iii) an acetate group, iv) an epoxide, v) a styrene, or vi) an acrylate
• second compatabilisers which are interfacial copromoters selected from a group comprising either i) polyvinyl acetate, ii) ethylene vinyl acetate, iii) polyacrylonitrile or high nitrile resin, iv) acrylamide or polyacrylamide, v) a phenolic resin, vi) an acrylate polymer, vii) a halogenated polymer, viii) maleic anhydride or polymaleic anhydride, or ix) a bismaleimide
• thermoplastics selected from a group comprising either i) polyurethanes, ii) polyesters, iii) polyamides, iv) acrylates, v) acrylonitrile butadiene styrene, vi) polyolefins, or vii) cellulose esters.
• thermoplastic is more polar than natural rubber, such thermoplastics including polyurethanes, polyesters, polyamides, acrylates, acrylonitrile butadiene styrene or celluloses. It will be appreciated that some slow curing rubbers such as butyl rubber may not be particularly suitable in the practice of this invention because of their undesirable curing properties. Further, when the thermoplastic is selected from the group of polyolefins and the first compatabiliser is selected from the group of halogenated polymers, then preferably the second compatabiliser is not a phenolic resin or a halogenated polymer.
• thermoplastic used in the composite may be derived from recycled thermoplastics.
• Suitable polyolefins may be selected from the group including but not limited to high density polyethylene (HDPE), linear low density polyethylene (LLDPE), polypropylene homo polymer (PPHP), polyproylene copolymer (PPCP), poly(ethylene-co-propylene) (PEP).
• Polyolefins may be chosen for their high chemical resistance, electrical properties, high impact strength and low cost.
• thermoplastic polyamides include those that are crystalline or resinous high molecular weight copolymers or terpolymers.
• Polyamides may be prepared by polymerisation of one or more lactams such as caprolactam, pyrrolidinone, lauryllactam, or by condensation of diamines with diacids.
• Suitable polyamides include polymeric amides having recurring amide groups as part of the polymer backbone and may be chosen form the list including but not limited to polycaprolactam (Nylon-6), polylauryllactam (Nylon- 12), polyhexamethyleneadipamide (Nylon-6,6), polyhexamethyleneazelamide (Nylon-6,9), polyhexamethylenesebacamide (Nylon- 6,10), polyhexamethyleneisophthalamide (Nylon-6,IP), the condensation product of 1 1-aminoundecanoic acid (Nylon- 1 1) and the product of reaction between castor oil and sebasic acid.
• Suitable polyamides also include copolymers with other monomers. Polyamides may be chosen for their high impact strength, shock resistance, high tensile strength, ability to absorb moisture and/or their flame resistance.
• Suitable polyurethanes may include but are not limited to thermoplastic polyurethane resins based on caprolactam, ethylene glycol or ethyl or propyl adipate reacted with isocyanates and having a Shore A hardness of 80 to 90. Polyurethanes may be chosen for their desirable properties that may include their toughness and abrasion resistance.
• thermoplastic polyesters may be suitable and the polyesters may be prepared by condensation of one or more dicarboxylic acids, anhydrides or esters and one or more diol.
• Cellulosic polyesters are particularly suitable for the present invention and suitable cellulosics can include but are not limited to polymers of cellulose acetate, cellulose acetobutyrate or cellulose propionate. Suitable polyesters may also include polycarbonates.
• Suitable acrylic thermoplastics may include polymethyl methacrylate and these may be added to improve heat stability and coulourability of a final composition. Further, acrylics tend to be highly crystalline and therefore they are preferable when a highly crystalline final composition is required.
• the rubber thermoplastic compositions of the present invention may be divided into one of four classes depending upon the properties of the composition, namely rigid, toughened, semi-toughened or soft natural rubber thermoplastic compositions.
• the rubber thermoplastic compositions of the present invention are intended for use as thermoplastic elastomers that are processable and can be fabricated into parts by conventional techniques used for thermoplastic materials.
• the mechanical properties of the compositions of the present invention may be determined using the standard test procedures used in the rubber and thermoplastics industries.
• Thermoplastic rubber compositions of the present invention may be used for making articles used in the mechanical, automotive, construction, textile, sports goods, irrigation, cable, agriculture, footwear, pipe/hose and tyre and wheel industries.
• the articles may be made by extrusion, injection moulding or compression moulding.
• the invention might also be said to reside in an article made from a thermoplastic composite of the present invention, which article may be formed by any suitable method used in the thermoplastics industries, which methods may include extrusion, injection moulding or compression moulding.
• the invention might also be said to reside in a method of forming a natural rubber thermoplastics composite, including the steps of forming a rubber matrix of the first aspect of the invention, and combining the rubber matrix with a plastics phase under conditions of dynamic vulcanisation.
• Figure 1 shows weight loss versus temperature results of differential scanning calorimetry of a sample 'soft' grade sample of natural rubber/nitrile rubber/polyolefin
• Figure 2 shows heat flow versus temperature results of differential scanning calorimetry of a sample 'soft' grade sample of natural rubber/nitrile rubber/polyolefin
• Figure 3 shows loss modulus versus temperature results of dynamic mechanical analysis of a sample 'soft' grade sample of natural rubber/nitrile rubber/polyolefin
• Figure 4 shows weight loss versus temperature results of differential scanning calorimetry of a sample 'intermediate' grade sample of natural rubber/nitrile rubber/polyolefin
• Figure 5 shows heat flow versus temperature results of differential scanning calorimetry of a sample 'intermediate' grade sample of natural rubber/nitrile rubber/polyolefin
• Figure 6 shows loss modulus versus temperature results of dynamic mechanical analysis of a sample 'intermediate' grade sample of natural rubber/nitrile rubber/polyolefin
• Figure 7 shows weight loss versus temperature results of differential scanning calorimetry of a sample 'rigid' grade sample of natural rubber/nitrile rubber/polyolefin
• Figure 8 shows heat flow versus temperature results of differential scanning calorimetry of a sample 'rigid' grade sample of natural rubber/nitrile rubber/polyolefin
• Figure 9 shows loss modulus versus temperature results of dynamic mechanical analysis of a sample 'rigid' grade sample of natural rubber/nitrile rubber/polyolefin.
• the natural rubber is pre-masticated in an internal mixer or a mill together with the first and second compatabilisers and peptisers (if required) for about 5 minutes or less, although if a mill is used the process may take more than 10 minutes.
• the time is dependent upon the viscosity of the rubber.
• the temperature during mixing or milling preferably should not exceed 120°C. Any additives such as fillers are added during the mastication.
• the stock is normally viscosity stabilised, slabbed and left to mature with polyethylene sheets between each patch. The maturation period may be 6-12 hours.
• the rubber matrix is then cut into strips and added to a Branbury mixer or mixer extruder (e.g.
• thermoplastics are then added and in teh case of a Branbury mixer after mixing for 5 minutes an antioxidant is added and after a further 1 minute the resulting composite is fed onto an extruder in a hot condition and extruded and pelletised. The product is then extruded and pelletised on a strand pelletiser or a die face cutter.
• Phenolic resin Phenolic formaldehyde resin for heat stability/hardness (Hylak; Bakelite) Tin chloride Stannous (II) chloride : a selection from commercial grades available Zinc stearate Commercial grade HVA 2 Bismalemide (DuPont)
• Dehydrated castor oil may also be added if a plasticiser is required.
• HDPE High Density polyethylene melt flow index (mfi) 3; moulding grade.
• EVA Ethylene vinyl acetate : preferred grade 28% vinyl acetate content; mfi 2
• LLDPE Linear low density polyethylene : moulding grade; mfi 3 (Exxon)
• NR, NIR and/or NBR, HDPE and EVA were masticated in a Barbender mixer at 80 m and 100°C.
• the masticated rubber matrix along with LLDPE, HVA 2 , peroxide and zinc stearate are blended in an internal mixer (Branbury) at 180-190°C.
• Antioxidant is added at the end of the blending process.
• the material is extruded and pelletised as in Example 1.
• EXAMPLE 2.3 Rubber thermoplastic compositions with nitrile first compatabiliser and polyolefin thermoplastics and a bismaleimide compatabiliser
• NR Natural Rubber SMRLCV or ISNRLCV or equivalent; low protein and low dirt grades are preferable.
• HMHDPE High molecular weight high density polyethylene : mfi 2 (Exxon)
• LDPE Low density polyethylene general pu ⁇ ose; mfi 2 (Exxon)
• Zinc stearate a selection from commercial grades available Anti-oxidant Wingstay L/100 (Goodyear) or Santowhite (Monsanto)
• Titanium dioxide, carbon black or Tunivan (P) [Ciba Geigy (Novartis)] can be added for additional UV protection.
• PPHP - can be substituted by PPCP, PPHP to balance mould shrinkage.
• Vanillin (1-2 phr) of can be added to the compound for odour.
• Fillers like CaCO3/talc can be loaded up to 30%.
• Rubbers are masticated with 10 parts of paraffinic oils, 0.08 parts of Renacit-11 (Bayer) and/or 0.04 parts of DCO (Dehydrated Castor oil).
• the masticated rubber along with polyolefins, HVA2, peroxide and zinc stearate are blended in an internal mixer at 180-190°C.
• Antioxidant is added at the end of the blending process.
• the same material is extruded and pelletised according to Example 1. It is desired that the material is allowed to expand to the maximum to avoid future mould shrinkage.
• a 'soft' grade composition comprising: natural rubber (15 parts), nitrile butadiene rubber (30 parts), linear low density polyethylene (5 parts), ethylvinyl acetate (25 parts), engage (20 parts), HVA 2 (0.75 parts), peroxide (0.075 parts),
• MBTS (0.25 parts), zinc stearate (1 part) and antioxidant ( 1 part) was subjected to thermogravimetric analysis, differential scanning calorimetry and dynamical mechanical analysis as described.
• DSC Differential scanning calorimetry
• DSC was conducted using DSC 2920 from TA Instruments. A weighed amount of sample was analysed from -100°C to 400°C under nitrogen flow, and heating rate of
• DMA was carried out using DMA 2980 (TA Instruments) operating in tension mode from -140°C to 100°C at 1 Hz frequency and 0.08% strain amplitude, at programmed heating rate of 2°C/min. Liquid nitrogen was used to achieve sub-ambient conditions. Glass transition temperature (Tg) of the samples was determined from tan3 curves.
• TGA Figure 1 shows weight loss versus temperature of the sample. The results show the approximate composition of 53% rubber (PU added), 25% plastic, 13% plasticiser and 9% other material.
• the first metling point is broad at temperature 118°C with heat of fusion of 3.66J/g.
• the second melting point is at 157°C with heat of fusion of 6.47 J/g.
• the glass transition temperature was selected as the peak position of the tan3 when plotted vs temperature. From Figure 3 two sharp glass transitions can be noticed, the first at -60°C and the second glass transiton at -21°C. The graph indicates a storage modulus of 18.59 MPa at 25°C.
• An 'intermediate' grade composition comprising: natural rubber (20 parts), nitrile butadiene rubber (30 parts), high density polyethylene (10 parts), ethylvinyl acetate (20 parts), linear low density polyethylene (20 parts), HVA 2 (0.75 parts), peroxide (0.07 parts),
• MBTS (0.25 parts), zinc stearate (1 part) and antioxidant (1 part) was subjected to thermogravimetric analysis, differential scanning calorimetry and dynamic mechanical analysis using the methods as described in Example 7.
• TGA Figure 4 shows weight loss versus temperature of the sample. The results show a first step of natural rubber weight loss that is not a sharp peak and the total amount is 26% mixture of natural rubber and other rubber. A second step is the decompositions of plastics in the amount of 71% and a residue of 3%.
• DSC Figure 5 shows two melting points and two broad endothermic decompsoitions.
• the first metling point is at temperature 125°C with heat of fusion of 15. lOJ/g.
• the second melting point is at 162°C with heat of fusion of 36.32 J/g.
• the glass transition temperature was selected as the peak position of the tan ⁇ when plotted vs temperature. From Figure 6 two sharp glass transitions can be noticed, the first a sharp peak at -58°C, which represents that glass transition of the natural rubber and nitrile rubber indicating their compatability. A second broad glass transiton at 0.8°C is indicative of partially miscible polyolefins. The graph indicates a storage modulus of 298.85 MPa at 25°C.
• a 'rigid' grade composition comprising: natural rubber (6 parts), nitrile butadiene rubber (4 parts), polypropylene homopolymer (30 parts), polypropylene copolymer (30 parts), high molecular weight high density polyethylene (30 parts)
• HVA 2 (0.75 parts), peroxide (0.03 parts), zinc stearate (1 part) and antioxidant (1 part) was subjected to thermogravimetric analysis, differential scanning calorimetry and dynamic mechanical analysis using the methods as described in Example 7.
• TGA Figure 7 shows weight loss versus temperature of the sample. The results show a first step of natural rubber weight loss and the amount is 9% . A second step is the decompositions of polypropylene and polyethylene in the amount of 90% and a residue of 1%.
• DSC Figure 8 shows two melting points and a broad endothermic decomposition with several shoulders. The first metling point is at tempaerature 126°C with heat of fusion of 18.61J/g. The second metlting point is at 165°C with heat of fusion of 40.93 J/g.
• the glass transition temperature was selected as the peak position of the tan ⁇ when plotted vs temperature. From Figure 9 two broad glass transitions can be noticed, the first at -52°C, and the second broad glass transiton at 9.7°C in indicative of partially miscible polyolefins.
• the graph indicates a storage modulus of 630 MPa at

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