Modification, impact

The improvement of physical properties, particularly impact strength, is the role of an important group of additives, both for thermoplastics and thermosets. The aim is to compensate for inherent brittleness, or embrittlement occurring at subzero temperatures, notch sensitivity, and crack propagation. The mechanism is normally to introduce a component that can absorb the energy of an impact, or dissipate it. One of the main methods is to introduce microscopic particles of rubber, but there is also considerable interest in the surface treatment of fillers and other additives, such as pigments, to give them an impact modification function also and so add to their value. 

An key requirement of an impact modifier is its ability to bond, either mechanically or, more recently, chemically, with the matrix polymer. It is important, however, to differentiate between impact modification and reinforcement. In some polymer matrices, reinforcement such as glass fibre actually makes the matrix more brittle (and an impact modifier has to be included). 

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. 

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DuPont—Dow is the primary suppHer of these polymers. There is an estimated 18,000 t of these elastomers used per year. The main uses of CPE are in constmction, automotive, and electrical appHcations. These include power steering hose, electrical cords used in low voltage appHcations (extension cords, ignition wire), pond liners, and as a plastic modifier to improve impact modification. 

Elliot [38] has reported that interfacial adhesion in the NR-PP blend can be enhanced by the addition of small amounts of HOPE. Addition of HDPE does give some improvement in the notched Izod impact strength of NR-PP blend (Fig. 7). The effect of HDPE on the impact modification of NR-PP is associated with the improved crystallinity of PP, enhanced by HDPE. During the mill mixing of NR and PP, chain scission may occur to give polymeric radicals that, on reaction with... 

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]. 

PBT has also been blended with styrene-maleic anhydride (SMA) copolymers giving materials similar to the ABS blends. Impact modification appears to be more difficult, and one must always be attentive to possible melt reaction with the anhydride, or its ring-opened acid forms, and the PBT resin. 

The PARALOID EXL range also includes PARALOID EXL 2314, an acrylic impact modifier with reactive functionality for PET impact modification. 

Block copolymers are widely used industrially. In the solid and rubbery states they are used as thermoplastic elastomers, with applications such as impact modification, compatibilization and pressure-sensitive adhesion. In solution, their surfactant properties are exploited in foams, oil additives, solubilizers, thickeners and dispersion agents to name a few. Particularly useful reviews of applications of block copolymers in the solid state are contained in the two books edited by Goodman (1982,1985) and the review article by Riess etal. (1985). The applications of block copolymers in solution have been summarized by Schmolka (1991) and Nace (1996). This book is concerned with the physics underlying the practical applications of block copolymers. Both structural and dynamical properties are considered for melts, solids, dilute solutions and concentrated solutions. The book is organized such that each of these states is considered in a separate chapter. 

In an oversimplication, it is the combination of high strength, high modulus, creep resistance, dimensional stability, and impact modification of the brittle matrices which leads to the selection of fibrous glass in composites. 

US 5,028,681 (American) 1991 Novel poly(imide siloxane) block copolymers and process for their preparation General Electric EN Peters Injection moldable block copolymers with high IV and excellent chemical/physical properties. Blends useful for impact modification Novel siloxane-imide block copolymers and a process for their preparation are covered. The method involves reacting a hydroxy-terminated polyimide oligomer with a siloxane oligomer with dimethylamino, acetyl or chlorine end-groups... 

Zolotnitsky M (1997) Composition and method for impact modification of thermoplastics. US Patent 5648426... 

Plastic-Plastic Blends. In recent years, a number of alloys of two or more plastics which are believed to be largely immiscible have achieved commercial prominence or are being considered for commercialization. The rationale for these products is different than simply impact modification and generally involves the concepts of property combinations and cost dilution. We will consider a number of examples of such systems. 

ACHIEVING LOW GLOSS IN VINYL SIDING WITH ACRYLIC IMPACT MODIFICATION... 

Impact Modification of Polysulfone with Polysulfone/Poly(dimethylsiloxane) Block Copolymers... 

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