MFCs prepared from blends of condensation polymers

The described peculiarities of MFCs can be expected and realized when the blend partners are condensation polymers or, at least, functionalized polyolefins. The latter restriction however, concerns only the self-compatibilization effect but by no means the basic principles of MFC manufacturing, i.e., MFCs can be prepared also from polyolefin partners provided the basic temperature requirements for their preparation are satisfied. 

Microfibrillaj reinforced composites processed via injection molding have shown that the tensile strength of the final MFC product can be 50% higher than that of the neat PA6 and only 15% lower than that of 30% GF-reinforced PA6. The modulus is more than double that for neat PA6 and only 35% lower than that of GF-reinforced PA6 [45]. Compression molded samples comprising three layers of drawn PET/PA6 filaments placed either in parallel (0)3 or crossplied (0/90/0) have also been tested [90]. Measurements a and E) show that the maximum a of the MFC with parallel alignment (0)3 is almost twice as high as that of the crossplied composite (0/90/0), whereas the E-values of the samples are almost the same. At the same time, compared to neat PA6 and an undrawn PET/PA6 blend, a has been shown to increase by a factor of almost three [90]. 

Microfibrillar composites from blends of condensation polymers with polyolefins 

Special attention was paid to the structure-property relationships of blends involving polyolefins, especially PP and PE, as lower-melting components acting as matrices in MFCs, and PET as the higher-melting component, forming the microfibrillar reinforcing elements [45]. 

Concerning the mechanical properties of the PP/PET blend, as expected, the as-extruded material is characterized by the poorest strength and elastic properties (a and E, respectively) while its deformational ability, e, is the highest. Subsequent cold drawing leads to an almost ten- and sixfold increase in a and E, respectively, and to a drastic decrease in s. 

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What could be the reason for these superior mechanical properties of MFCs prepared from blends of condensation polymers and polyolefins It could hardly be the same as in the case of blends of condensation polymers the perfect adhesion between matrix and reinforcing microfibrils are due to the formation of chemical bonds between them as outlined above. Neither could it be related to a better aspect ratio of the reinforcement, since the sizes of microfibrils do not depend that strongly on the chemical composition of the blend. 

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