In Blends with Thermoplastics

A considerable amount of work has been carried out to establish if it is possible to produce good-quality rubber/thermoplastic blends by incorporating waste rubber crumb, whether surface-activated or not, into thermoplastics matrices. This work has often been carried out using commodity semi-crystalline thermoplastics, such as low-density polyethylene (LDPE), high-density polyethylene (HOPE) and polypropylene (PP), with the aim to produce final products that are either modified (e.g., improvements in impact strength) or have properties that are usually associated with thermoplastic rubbers. 

The properties of the resulting blends are dependent on a number of factors  

Murphy and co-workers [3] have looked into the effect on physical properties of blending ultrafine rubber particles into thermoplastics. A large range of blends were produced using a munber of recycled thermoplastics and recycled rubbers in a batch process. The influence that the particle size of the rubber, the total amount of recycled rubber, and the degree of compatibilisation had on the physical properties was determined and reported. 

The possibility of blending waste injection-moulded PP with waste tyre crumb has been explored by a team drawn from both Loughborough and Moratuwa universities [5]. The two starting materials were blended in a range of different proportions, and samples of each were fully characterised using a range of physical tests and analytical methods. The team was particularly interested in how the blend ratio influenced the crystallinity and phase morphology of the material and how this affected its processibility and mechanical properties. 

Work carried out in China and Korea [6] has looked into the role that bitumen and compatibilisers can play in waste tyre rubber/waste PP blends. In addition to assessing the effect of the level of bitumen, the study also investigated the effect that various compatibilisers had on the properties of the final products. The team carried out this assessment using a universal testing machine, a scanning electron 

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Considerable amounts of EPM and EPDM are also used in blends with thermoplastics, eg, as impact modifier in quantities up to ca 25% wt/wt for polyamides, polystyrenes, and particularly polypropylene. The latter products are used in many exterior automotive appHcations such as bumpers and body panels. In blends with polypropylene, wherein the EPDM component may be increased to become the larger portion, a thermoplastic elastomer is obtained, provided the EPDM phase is vulcanked during the mixing with polypropylene (dynamic vulcani2ation) to suppress the flow of the EPDM phase and give the end product sufficient set. 

In the context of this chapter, the use of thermoplastic starch in blends with thermoplastic resins is of the main interest. As shown in Table 16.11, several blends have been developed, e.g., with vinyl alcohol copolymers (EVAl), polyolefins, aliphatic polyesters such as poly-e-caprolactone (PCL) and its copolymers, or polymers of glycols (e.g., 1,4-butanediol) with succinic, sebacic, adipic, azelaic, decanoic or brassihc acids, PCL + PVC. Compatibilization is possible by amylose/EVAl V-type complexes, starch grafted polyesters, chain extenders like diisocyanates, epoxies, etc. [Bastioli et al., 1992, 1993]. 

Styrene-butadiene-styrene (SBS) rubbers are either pure or oil-modified block copolymers. They are most suitable as performance modifiers in blends with thermoplastics or as a base rubber for adhesive, sealant, or coating formulations. SBS compoimds are formulations containing block copolymer rubber and other suitable ingredients. These compounds have a wide range of properties and provide the benefits of rubberiness and easy processing on standard thermoplastic processing equipment. 

Steller, R., Zuchowska, D., Meissner, W., Paukszta, D., Garbarczyk, J., Crystalline structure of polypropylene in blends with thermoplastic elastomers after electron beam irradiation. Radiation Physics and Chemistry 2006, 75, 259-267. 

Van Gooswilligen G. and W.C. Vonk. 1986. The Role of Bitumen in Blends with Thermoplastic Rubbers for Roofing Applications. Thermoplastic Rubbers Technical Manual TR 8.16. Chertsey, Surrey, UK Shell Bitumen, UK. 

Most common polymers used in blending with thermoplastic starch... 

Interestingly, aPP found less use in blends with thermoplastic polymers irrespective of the high number of related patents. The new generation aPP, produced by metallocene synthesis, may change this scenario (see also the chapter Elastomeric polypropylene homopolymers using metallocene catalysts ). Blending of HMW-aPP with polyolefins may result in a new mechanical property profile, e.g. rubberlike resilience. Such products may compete with those made of flexible PVC. 

A final application is in blends with thermoplastics or other polymeric materials. Styrenic block copolymers are technologically compatible with a surprisingly wide range of other polymers. Blends with many other thermoplastics have improved impact resistance. These block copolymers can also be used as compatibilizers— that is, they can produce useful products from blends of thermoplastics that otherwise have poor properties [6]. 

CPE is also used in blends with thermoplastics as an impact modifier. 

Jagisch, F. C., Performance of Vistanex LM Polyisobutylene in Blends with Thermoplastic Hydrocarbon Materials, Exxon Chemical Technical Report TB-AP-35, Baton Rouge, 1979. 

Further information in particular areas can be obtained by using recent reviews. For example, readers who would like to obtain more information on the use of waste rubber in blends with thermoplastics, thermosets and virgin rubber compounds can obtain it in an extensive review that has been produced recently by Karger-Kocsis, Meszaros and Barany [1], This review also surveyed the methods available to reclaim waste rubber, the surface treatment of rubber particles to improve interfacial adhesion in blends, and the principals underlying the compatibilisation of waste rubber within the host matrix. 

Thermoplastic chlorinated polyethylenes are seldom used on their own but primarily in blends with other polymers, particularly PVC. If chlorination is taken to a level at which the polymer is only semi-compatible with the PVC, a blend with high impact strength may be obtained. In these circumstances the material is classified as an impact modifier. 

Materials with totally new property combinations may be achieved by blending two or more polymers together. Through blending of thermotropic main-chain LCPs with engineering thermoplastics, the highly ordered fibrous structure and good properties of LCPs can be transferred to the more flexible matrix polymer. LCPs are blended with thermoplastics mainly in order to reinforce the matrix polymer or to improve its dimensional stability, but LCP addition may modify several... 

A route to compatibility involving ionomers has been described recently by Eisenberg and coworkers [250-252]. The use of ionic interactions between different polymer chains to produce new materials has gained tremendous importance. Choudhury et al. [60] reported compatibilization of NR-polyolefin blends with the use of ionomers (S-EPDM). Blending with thermoplastics and elastomers could enhance the properties of MPR. The compatibility of copolyester TPE, TPU, flexible PVC, with MPR in aU proportions, enables one to blend any combination of these plastics with MPR to cost performance balance. Myrick has reported on the effect of blending MPR with various combinations and proportions of these plastics and provided a general guideline for property enhancement [253]. 

Bull A.L. and Holden G., The use of thermoplastic mbbers in blends with other plastics. Paper presented in Rubber Division, American Chemical Society, April 1976 and J. Blast. Plast., 9, 281 1977. 

PVC, another widely used polymer for wire and cable insulation, crosslinks under irradiation in an inert atmosphere. When irradiated in air, scission predominates.To make cross-linking dominant, multifunctional monomers, such as trifunctional acrylates and methacrylates, must be added. Fluoropolymers, such as copol5miers of ethylene and tetrafluoroethylene (ETFE), or polyvinylidene fluoride (PVDF) and polyvinyl fluoride (PVF), are widely used in wire and cable insulations. They are relatively easy to process and have excellent chemical and thermal resistance, but tend to creep, crack, and possess low mechanical stress at temperatures near their melting points. Radiation has been found to improve their mechanical properties and crack resistance. Ethylene propylene rubber (EPR) has also been used for wire and cable insulation. When blended with thermoplastic polyefins, such as low density polyethylene (LDPE), its processibility improves significantly. The typical addition of LDPE is 10%. Ethylene propylene copolymers and terpolymers with high PE content can be cross-linked by irradiation. ... 

Starch is made thermoplastic at devated temperatures in the presence of water as a plasticizer, allowing melt processing alone or in blends with other thermoplastics (192—194). Good solvents such as water lower the mdt-transition temperature of amylose, the crystalline component of starch, so that processing can be done well bdow the decomposition—degradation temperature. 

Elastomers are often blended with thermoplastics in order to combine in the final product the thermoplastic resin processability and elastomeric behavior in the solid state. 

One of the major areas for potential involves the synthesis of polyolefin block copolymers. A PP-EPR-PP or PE-EPR-PE block copolymer could have large potential as is or in blends with other polyolefins. PE-EPR-PE block copolymers have been synthesized via anionic polymerization of butadiene-isoprene-butadiene ABA block copolymers followed by hydrogenation [Mohajer et al, 1982 Rangarajanout et al., 1993]. These materials would have utility in hot melt adhesive formulations as well as general-purpose thermoplastic elastomer applications. Improvements on the synthesis procedures to offer viable approaches to polyolefin block copolymers could open up a new class of commercial polyolefins. In summary, several opportunities exist for new combinations of commercial blends from the list of commodity polymers. 

The common electrically conductive polymers can generally be prepared in film form, however, not thermoplastic. In several cases, the conducting polymers are brittle and thus have marginal mechanical utility. Blends with thermoplastics have been studied to search for solutions to these problems. 

Some liquid Cl can be plasticizers (PI) of the polymer binder at the same time. Many oil-soluble Cl show this property towards polyoileflns. The Cl soluble in PI, solvents and other CM expand their limits of blending with thermoplastic binders. 

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