Morphology and Phase Interactions

The influence of copolymer structure on the compati-bilizing effectiveness has been extensively examined for several blends of polyolefins. Addition of graft (PS-g-LDPE) and block copolymers for the compatibilization of LDPE/PS blends has been reported by various authors, resulting in large improvement of interfacial adhesion and mechanical properties [88,89]. Ethylene-propylene copolymers (EP) with block and random distribution of units have been used as compatibilizers for blends of PP with HDPE, LDPE, and LLDPE [90,91], and EPDM-g-PP copolymers were successfully employed for the compatibilization of EP/PP blends [92]. 

The noncompatibilized blend PET/PP (75/25) shows a neat phase separation of the components with an average size of PP particles of about 6 pm (Fig. 10.21a). In the compatibilized blends the average size of the minor phase decreased to about 2 pm with addition of SEES (10 phr) (Fig. 10.21b) and to about 1 pm with SEPSEP (10 phr) (Fig. 10.21c). 

The compatibilizing effectiveness of the various block copolymers is related to several aspects, such as the copolymer structure, the molecular weight, the concentration, and the location at the interface [89, 94]. Binary blends of PP and block copolymers were also examined in order to assess the compatibility between the polyolehn components [95]. It was found that binary blends PP/SEP and PP/SEBS (where PP is the major component) showed a finely dispersed copolymer phase with a nearly homogeneous morphology (see Fig. 10.21d). 

2 Blends Compatibilized by Addition of Functionalized Polymers The addition of functional/ reactive polymers to immiscible blends is a very versatile method to promote the compatibUization of a large number of heterogeneous polymer systems. Usually, a polymer chemically similar or identical to one of the 

The addition of functionalized polymers offers the advantage to achieve the blend compatibUization (emulsifying effect) by using a smaU amount (a few percent) of modified component. This method has found large application, especially for blending of polyolefins with polar polymers, such as polyamides, polyesters, polyethers moreover, it can be useful in the preparation of polymer composites with various types of fillers [96]. 

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