Polyolefin matrix

TPOs, comprising TPEs with a polyolefin matrix and an unvulcanized rubber. They can be produced by blending or by block copolymerization of polypropylene and EPDM (reactor TPOs). Sometimes TPVs are included in TPOs. 

R + R. OH - RH + R. o flow a combination of primary and secondary antioxidants functions in a SCHEME2.8 Stabilizing polyolefin matrix.82 Some metal-chelate scavengers may also be based on activity of chain-breaking, a tertiary phenolic structure, thereby introducing two antioxidant properprimary antioxidants. ties into the same molecule. 

It was recently reported [79,80] that grafting through esterification between refiner-ground pulp and MA-modified polypropylene occurred when they were kneaded at 180°C for 10 min. This resulted in an enhanced adhesion between the polyolefin matrix and the pulp fibers, giving high levels of physical properties to the composites [79]. 

For Oleflex TPO (PP and PE with a-olefin random copolymer), reactive processing (cross-linking) is used to get a finely dispersed morphology of copolymer dispersed in the polyolefin matrix. Recommended processing conditions are similar to those for neat PP or PE. For calendering, the melt temperature should be in the range 165-175°C. 

A number of polyolefin blends are routinely calendered. TPO s consisting of blends of PP or PE with a-olefin random copolymer Oleflex ) are suitable. The copolymer is finely dispersed as a rubbery phase in the polyolefin matrix. The blend is processed at conditions similar to polyolefins. For calendering, typical melt temperature is 165-175°C. 

The crystallization behavior and kinetics under isothermal conditions of iPP/SBH and HDPE/SBH blends, compatibilized with PP-g-SBH and PE-g-SBH copolymers, respectively, have been investigated (71). It has been established that the LCP dispersed phase in the blends plays a nucleation role for the polyolefin matrix crystallization. This effect is more pronounced in the polypropylene matrix than in the polyethylene matrix, due to the lower crystallization rate of the former. The addition of PP-g-SBH copolymers (2.5-10 wt%) to 90/10 and 80/20 iPP/SBH blends provokes a drastic increase of the overall crystallization rate of the iPP matrix and of the degree of crystallinity. Table 17.4 collects the isothermal crystallization parameters for uncompatibilized and compatibilized iPP/SBH blends (71). On the contrary, the addition of PE-g-SBH copolymers (COP or COP 120) (2.5-8 wt%) to 80/20 HDPE/SBH blends almost does not change or only slightly decreases the PE overall crystallization rate (71). This is due to some difference in the compatibilization mechanism and efficiency of both types of graft copolymers (PP-g-SBH and PE-g-SBH). The two polyolefin-g-SBH copolymers migrate to blend interfaces and... 

The effects of minor proportions of PVC and PS in the polyolefins are quite dramatic. As little as 5% of PVC or PS in LDPE reduces the impact strength (toughness) of the latter by about 65%. This results from their presence as separate phases in the polyolefin matrix which leads to rapid crack propagation on impact. The effect of PP is very much less 10% of PP in LDPE reduced the energy absorbing capacity (toughness) of the matrix by only 1 % and 20% of PP reduced it by only 5%. The addition of block copolymers which act as compatibilisers or more correctly solid-phase dispersants (SPDs) for a second incompatible phase reduces the size of the heterogeneous domains and improves impact resistance. However, a considerable concentration ( 20%) of SPD is required, which unacceptably increases the cost in most cases. 

The significant advance in Zi ler-Natta polymoization represented by the Reactor Granule Technology is not limited, however, to the incorporation and polymerization of olefinic monomers only. It has been extended to allow the incorporation of non-olefinic monomers into the polyolefinic matrix. 

Challenges include the usual nanocomposite problems such as the adhesion of the cellulose additives to the polyolefin matrix and fiber/matrix interface optimization. 

The addition of rigid particles into the polyolefin matrix can result in a number of desirable effects on the composite including increased stiffness, improved flame retardancy, and enhanced electrical properties. 

Fibers are classified as natural or synthetic. Fibers are used as a reinforcement material to increase the mechanical properties of polymer composites [31]. Synthetic fibers have been successfully used as the reinforcing material in composites such as carbon fiber, glass fiber, and Kevlar fiber. Glass fiber is a well-known example of a reinforcement material for polyolefin matrix. Polypropylene is a composite of increasing interest in automotive and other applications [32]. Figure 6.3 illustrates a glass fiber-reinforced polypropylene matrix. 

Fig. 6.4 Cross section of a natural fiber-reinforced polyolefin matrix with coupling agent...

The possibility of manufacturing nano-composites materials with tailored properties at low cost has gained much interest. In fact, there is already more than two decades of research on those materials. Particular interest has been paid to clay nano-platelets and their composites with non-polar thermoplastic polyolefin matrixes, namely polypropylene (PP). 

Gauthier R. Gauthier H. and Joly C. Comjjatibifization between lignocellulosic fibers and a polyolefin matrix Proceedings of the Fifth International Conference on Woodfiber-Plastic Composites, Forest Products Society, Madison, WI, May 1999, p. 153... 

Results of many researches confirm the presence of TCL as the effect of nucleation ability of different substances. Among the factors inducing transcrystallization in polyolefin matrix, the following fillers can be listed ... 

Composites of isotactic PP with Hemp fibers with various compatibilizers (PP-g-GMA, SEES, SEBS-g-GMA) were studied. All modified composites showed improved fiber dispersion in the polyolefin matrix and higher interfacial adhesion when compared with the unmodified system (PP/Hemp) as a consequence of chemical bonding between fiber and polymer. The spherulitic morphology and crystallization behavior of PP were changed in the composites due to the nucleating effect of Hemp fibers. All composites displayed higher tensile modulus (about 2.9 GPa) and lower elongation at break compared with plain PP [41]. 

Shebani et al. [20] noted that removing extractives improved the thermal stability of different wood species. Therefore, using extracted wood for the production of wood-plastic composite (WPCs) would improve the thermal stability of WPCs. Because wood and other bio-fibres easily undergo thermal degradation beyond 200°C, thermoplastic matrix used in the composites is mainly limited to low-melting-temperature commodity thermoplastics like polyethylene (PE) and polypropylene (PP). However, the inherently unfavourable thermomechanical and creep properties of the polyolefin matrix limit some structural applications of the materials. 

Comparison of the effects of mica, glass fibers, talc, calcium carbonate on the properties of a polyolefin matrix (unmodified and chemically modified by maleation)... 

Patty acid (stearic, isostearic) and other polar coupling agent effects on rheology and properties of CaC03 filled polyolefins are discussed in detail in Chapter 6. The beneficial effects of maleated PP in filled PP compounds are shovm in Table 6.9. Modification of the polyolefin matrix of Table 16.2 by maleic anhydride grafting through reactive extrusion increases the tensile and fiexural and unnotched impact... 

Note Fiberglass OCF457AA, Owens Corning Suzorite mica200H-K CaCOs Atomite/Microwhite 25, ECC Intern. CaC03 Kotamite, Coated ECC Intern. Talc, Microtalc MP1250, Pfizer Matrix, polyolefin matrix based on at least 80% HDPE, modified with peroxide/maleic anhydride in twin-screw extruder. 

Even PE, PP and polyvinyl chloride resins, still the most commonly used thermoplastic polymeric materials with wood, have low thermal stability above 200 °C. However, their inherently undesirable mechanical properties, such as the creep-resistant properties of the polyolefin matrix, have impeded further applications of the wood plastic composites (WPG) as structural composite materials. In attempts to overcome these drawbacks, attention has been given to the silane-crosslinking of wood/PE composites [38], the use of high-performance engineering thermoplastics such as Nylon 6 [39] as a single polymeric matrix, the modification of the matrix by incorporation of organoclay [40], and stretching wood/PP composites [41]. 

In the case of MFCs, the presence of a PET component in the polyolefin matrix speeds up the rate of crystallization by creating heterogeneous nuclei for the matrix polymer. As well as this, microfibrillar blends are known to cr5 stalhze faster than their conventional blend partners, because their higher dispersed phase surface area provides more of these nucleation sites [20,21]. 

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