Poly modification, blending with

As with other rigid amorphous thermoplastic polymers such as PVC and polystyrene (see the next chapter) poly(methyl methacrylate) is somewhat brittle and, as with PVC and polystrene, efforts have been made to improve the toughness by molecular modification. Two main approaches have been used, both of which have achieved a measure of success. They are copolymerisation of methyl methacrylate with a second monomer and the blending of poly(methyl methacrylate) with a rubber. The latter approach may also involve some graft copolymerisation. 

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]. 

Pullulan films have several other advantages. The films are colorless, tasteless, odorless, transparent, resistant to oil and grease, and heat sealable. The properties of the films can be modified by chemical modification of pullulan, blending with poly-vinylalcohol, gelatin, or amylose, and by addition of plasticizers. These properties indicate that pullulan can be used as a coating or packaging for foods to prevent their oxidation. This is the only apparent outstanding application for pullulan. 

FrOlich et al. [ 140] investigated a system in which DGEBA was mixed with hydroxy-terminated poly(propylene oxide-block-ethylene oxide) as the rubber, with the nanoclay being a synthetic fluorohectorite treated with bis (2-hydroxyethyl) methyl tallow alkylammonium ions. The clay was first blended with rubber, before being dispersed into the reactive epoxy mixture. Modification of the rubber allowed variation in miscibility and differing morphologies and properties. If the rubber was miscible, the intercalated clay led to improved toughness. If the rubber is sufficiently modified, such as with... 

Sis et al. prepared composites based on poly (lactic acid) (PLA)/poly (butylene adi-pate-co-terephthalate) (PBAT)/kenaf fiber using a melt blending method [39]. A PLA/ PBAT blend with the ratio of 90 10 wt%, and the same blend ratio reinforced with various amounts of kenaf fiber were prepared and characterized. The addition of kenaf fiber reduced the mechanical properties sharply due to the poor interaction between the fiber and polymer matrix. Modification of the composite by (3-aminopropyl)tri-methoxysilane (APTMS) showed improvements in mechanical properties, increasing up to 42.5, 62.7 and 22.0% for tensile strength, flexural strength and impact strength, respectively. The composite treated with 2% APTMS successfully exhibited optimum... 

Furthermore, the C=C bonds in the natural rubber structure might induce poor thermal and oxidative resistance in the natural rubber blends. Thus, Thawornwisit and coworkersproposed the preparation of hydrogenated natural rubber, which is one of the chemical modifications available to improve the oxidation and thermal resistance of diene-based natural rubber before blending with poly(methyl methacrylate-co-styrene). The poly(methyl methacrylate-co-styrene) was resistant to the outdoor environment and had excellent optical properties with a high refractive index, but it was extremely brittle and had low impact strength. Hydrogenated natural rubber could, however, be used as an impact modifier, as well as to improve its thermal and oxidative resistance for these acrylic plastics. 

It is well known that the Bruggeman EMA formula is derived by considering one of the constituents as a small sphere. A deviation from such an assumption required a modification the formula to include depolarization factor. Typically, a value of 0.333 is used as a default value in the EMA layer, which assumes a spherical shape of the inclusion. The other two extremes are 0, for a needle-like or columnar micro structure, and 1 for flat disks or a laminar microstructure. This type of transition was found for polyaniline/poly(methylmethacrylate) blend films presenting with a spherical-like microstructure at low sample concentration, whereas at relatively high concentrations the depolarization factor shifted to values closer to 1. This indicated the formation of flat microstructures due to aggregation of the polyaniline particles [8]. 

Polybutyleneterephthalate (PBT) is of growing interest as a material for injection molding. In fact, its rate of crystallization is faster than that of the other widely used linear polyesters such as polyethyleneterephtha-late (PET). However, PBT shows a low impact resistance, particularly at low temperatures. For this reason the uses of PBT are limited. The usual method to overcome this limitation is to add a second elastomeric phase to the PBT matrix. Rubber modification of PBT has been realized by melt blending with preformed rubbers such as poly(ethylene-co-vinylacetate) (EVA) and poly(ethylene co-vinylalcohol) (EVOH) [71], or by adding end-capped polymers to produce a second flexible component during PBT polymerization. 

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