Processing of single polymer composites using the concept of constrained fibers

The concept of "overheating" is one of the known methods for manufacturing single polymer composites. This concept is validated on two categories of semi-crystalline polymers: the drawable, apolar (i.e., isotactic polypropylene [iPP], ultra-high molecular weight polyethylene [UHMWPE]) and the less drawable, polar ones (i.e., polyethyleneterephalate [PET] and polyamides [PA]). The interchain interactions in apolar polymers are relatively weak and therefore a high degree of drawability can be obtained. Polar polymers on the other hand have relative strong interchain interactions, they are therefore less drawable. A shift higher than 20degreesC of the melting temperature can be obtained in case of highly extended iPP (draw ratios > 14). Uhra-drawn PE shows only 10degreesC overheating upon constraining and this is mainly due to the change in chain mobility for PE in the hexagonal phase. In case of PET and PA6, only draw ratios of 4 could be reached; however, temperature shifts of about 10degreesC for constrained fibers compared to unconstrained fibers could be measured. A proof of principle of the potential of the constraining concept for the manufacturing of single polymer composites is obtained by the preparation of single fiber model composites. The effect of the post-drawing conditions on overheating is examined in details on the example of iPP. It is concluded that both post-drawing temperature and ultimate draw ratio have a significant influence on the degree of overheating. POLYM. COMPOS., 26:114-120, 2005. (C) 2004 Society of Plastics Engineers