Use of compatibilizing agents

Blends of PPO and polyamide (PA, nylon) are incompatible but good properties can be obtained through the use of compatibilizing agents. The PPO is dispersed in a continuous nylon matrix in these blends. Because of the incompatibility of the two phases, the modulus decreases very little at the Tg of PA (71°C) and is maintained up to the Tg of the PPO phase (208°C). 

Blends made from incompatible polymers are usually weak. These poor blends are a result of high interfacial tension and poor adhesion between the two phases. For many years, blending of polymers was unsuccessful due to the fact that many polymers were incompatible. Lately new polymer blends have been successfully made by the use of compatibilizing agents. This has yielded polymers of unique properties not attainable from either of the polymer components of the blends. Sometimes these blends... 

Chain functionalized polymers or graft copolymers are of great technological importance. They are used as compatibilizing agents for immiscible polymer blends (8) and adhesive layers between polymer-polymer co-extruded surfaces (8). Currently, of all polymers sold, about 30% are in the form of compatibilized immiscible blends (9-12). Next we discuss a few examples of chain functionalization. 

In addition to these polar groups, many types of fluorocarbon and hydrocarbon groups have been attached to the silicone backbone, sometimes in combination with polar groups. Some of these materials are used as compatibilizing agents or for other surface active properties but they lie outside the scope of this chapter. 

One possible way of reducing interfacial tension and improving phase adhesion between PP-based blend phases is to use a selected copolymeric additive that has similar components to the blend, as a compatibilizer in the blend system. Well-chosen diblock copolymers, widely used as compatibilizing agents in PP-based blends, usually enhance interfacial interaction between phases of blends (15, 16), reduce the particle dimensions of the dispersed phase (16, 17), and stabilize phase dispersion against coalescence (16-18) through an emulsification effect, thus improving the mechanical properties (15-19). 

In case of the first studies using polymer compatibilizing agents, Anderson et al. of Dow Chemical in 1960 (135) irradiated polyethylene with y rays and... 

Polymers can be compatibilized in a number of ways. Polymers that act as mutual solvents can be used as compatibilizing agent, e.g., polycaprolactone in a blend of polycarbonate and poly(styrene-co-acrylonitrile). 

The isotactic polypropylene (iPP) was supplied by FiberVisions, Georgia, in the form of homopolymer pellets with a melt flow index of 35g/10 min (230 °C, 160 g) and a density of 0.91 g cm-3. The reinforcing filler was rice straw fibril and fibril aggregates (RSF) obtained from rice straw pulp fiber (Taonan paper and pulp company, Jihn ptrovinoe. North-east of China) that was cut to pass a screen (room temperature and relative humidity of 30%) with holes of 1 mm in diameter by a Willey mill before treatment. The maleated polypropylene (MAPP) was used as compatibilizing agent and Epolene G-3003 P has an acid number of 6 and a molecular mass of 125 722. 

Interesting results were reported by Mi et al. [19]. They analyzed polypropylene filled with bamboo fibers with the addition of polypropylene grafted with maleic anhydride. The use of the agent promoting the adhesion was aimed at improving interactions between the components. In case of systems polypropylene/bamboo fibers/compatibilizer, the TCL has been formed. This was explained by higher ability to nucleation of bamboo fibers in relation to MAPP-grafted polypropylene as compared to pure polymeric matrix. 

The properties of thermoplastic composites containing fibers as fillers are dependent on a number of parameters, which include the properties of the matrix material, the size and aspect ratio of the fibers, dispersion of the fibers and the interface. In development of these composites, two important issues need to be addressed, namely, the incompatibility between the natural fibers and polymer matrix, and the tendency of the fibers to form aggregates [67]. Additionally, the composites exhibit poor dimensional stability due to moisture absorption. The orientation of the fibers is also important. In short-fiber reinforced composites, the orientation of the fibers is usually random and therefore the properties of such composites are not as superior as those containing continuous fibers. Optimization of processing conditions and use of coupling agents/compatibilizers and treatment of fibers can enhance the properties of these composites. 

Upon analyzing the composite compatibilized with PP-g-M AH, a significant increase in stiffness was noted when compared to composites without the use of coupling agent. 

This conclusion seems to be confirmed by various studies on the addition of compatibilizing agents, which reduce the interfadal tension and make phase morphologies finer [92,93]. Wu [93] - based on a study of the system (polyamide-6,6) / (ethylene propylene copolymer) and [poly(ethylene terephthalate)]/(ethylene propylene copolymer), prepared in a modular co-rotating twin-screw extruder - suggests that final morphology may be correlated by using ... 

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