Modification of engineering thermoplastics

Modifying Processing Characteristics Lubricants, Mould Release Agents, 

Lubricating additives can have both performances and processing functions in plastics compounds, and (within strict limits) they can be either internal or external. The same or similar additives can he used to reduce the slip and blocking tendencies (of, for example, plastic films). 

Polystyrene (crystal) Clear-melt zinc stearate (bis-stearamides are usually adequate) secondaiy bis-amides assist How 

Metallic stearates in combination with glyceroi monostearate secondary bis-amides assist flow 

Styrene/acrylonltrlle Fatty acid amines, amides, secondary bis-amides 

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Blend of (1) and (2) type categories mostly include the modification of engineering thermoplastics with another thermoplastic or rubber. PS-EPDM blends using a low-molecular weight compound (catalyst) Lewis acid have been developed [126]. Plastic-plastic blends, alloys of industrial importance, thermoplastic elastomers made by dynamic vulcanization, and rubber-rubber blends are produced by this method. 

PESA can be blended with various thermoplastics to alter or enhance their basic characteristics. Depending on the nature of thermoplastic, whether it is compatible with the polyamide block or with the soft ether or ester segments, the product is hard, nontacky or sticky, soft, and flexible. A small amount of PESA can be blended to engineering thermoplastics, e.g., polyethylene terepthalate (PET), polybutylene terepthalate (PBT), polypropylene oxide (PPO), polyphenylene sulfide (PPS), or poly-ether amide (PEI) for impact modification of the thermoplastic, whereas small amount of thermoplastic, e.g., nylon or PBT, can increase the hardness and flex modulus of PESA or PEE A [247]. 

In the case of sPS, the problem of its brittleness can be even more acute since it has to compete with engineering plastics which possess an inherent toughness superior to that of sPS. For this reason, a good impact modification of this product is of paramount importance and may even be essential for its survival as a commercial thermoplastic. For this reason a chapter of this book has been dedicated to the impact modification of sPS using elastomers. Since rubber modification plays such an important role for styrene polymers, whether atactic or sydiotactic, we will first look at the methods of energy dissipation in these homopolymers on impact. 

Hedrick, J.L. Yilgdr, I. Wilkes, G.L. McGrath, J.E. Chemical modification of matrix resin networks with engineering thermoplastics. I. Phenolic hydroxyl terminated poly(aryl ether sulfone)-epoxy systems. Polym. Bull. 1985, 13, 201-208. 

Commingled plastics belonging to different chemical families, e.g., mixtures of PO s with either PA s or PEST s, or multicomponent mixtures comprising PO, PS, PVC, and engineering thermoplastics, etc. These materials require extensive compatibilization, sometimes molecular repair and impact modification. 

D. R. Paul, High performance engineering thermoplastics via reactive compatibihzation, in Modification and Blending of Synthetic and Natural Macromolecules, F. CiardeUi and S. Penczek (eds.), Kluwer Academic Publishers, Dordrecht, 2003, Chapter 14. 

Hed Hedrick, J. L., Yilgor, I., Jurek, M., Hedrick. J. C., Wilkes, G. L., McGrath, J. E. Chemical modification of matrix resin networks with engineering thermoplastics 1. Synthesis, morphology, physical behaviour and toughening mechanisms of poly (arylene ether sulfone) modified epoxy networks. Polymer 32 (1991) 2020-2032. 

Varley R, Thermoplastic Modification of a Trifunctional Epoxy Resin System, in PhD thesis. Department of Materials Engineering. 1998, Monash University Clayton, Melbomne... 

Polybutylene terephthalate (PBT) is one of the engineering thermoplastic polyesters that offers excellent performance for a variety of applications. Compounding of PBT with PO provides impact modification depending upon the type of PO used and the suitability of the compatibiliser [22-28]. 

Several approaches to compatibilizing PPE blends with commercial polyolefins (polypropylene, etc.) have been reported in the literature (Lee 1990 Kirkpatrick et al. 1989). Simultaneous compatibilization and impact modification of PPE/polypropylene blends was achieved by choosing selected types of styrene-ethylene/butylene-styrene block copolymers and PPE resin of low molecular weight (Akkapeddi and VanBuskirk 1992). A family of PPE/polypropylene alloys were commercially launched by G.E. in 2001, under the Noryl PPX trade name, and these are now sold by Sabic. Typical properties of a commercial PPE/PP blend are shown in Table 19.32. These PPE/PP blends are claimed to offer a balance of cost and performance between the TPOs and other higher-cost engineering thermoplastics such as nylons, modified PET, and PBT resins. Basically, the PPE/PP blends offer a balance of key properties stiffness, toughness, chemical, and heat resistance. 

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]. 

Early development concentrated on the improvement of standard plastics, such as the thermosets, phenolic and polyester resins, and the thermoplastics, polystyrene, PVC, and polyolefins. More recently there has been considerable development of impact modification systems for engineering thermoplastics. 

A common thread for engineering plastics in terms of their utilization in structural applications is their mechanical strength. Failures in thermoplastics may occur due to large stresses applied at low rates, fatigue or impact. Toughness is a major requirement in end use applications of engineering resins. The purpose of this entry is to provide an overview of the impact modification of these materials and to direct the reader to specialized publications for more in-depth discussions on this topic. 

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