The splitting tendency of uniaxially‐orientedPETtapes investigated with nano‐indentation, nano‐scratch, differential scanning calorimetry, and X‐ray

Abstract

Earlier, various additives werescreened to improve the weavability of poly(ethylene terephthalate) (PET) tape. For predicting the weavability, three tests had been used: tensile impact strength, fibrillar versus puckered fracture and an axial folding test. This paper shows the possibility of using a simple nano-indentation method to decide on the splintering tendency of uniaxially-oriented PET tapes, as a predictor for weavability. A plasticity index derived from the nanoindentation correlated with PET tapes that were, or were not, weavable. Nanoscratches applied parallel and perpendicular to the tape also showed differences that could be correlated to the splitting tendency. While investigating these tests methods, it was observed that pure uniaxially-oriented PET tape heat set at 140 C had a non-splintering character even without additives, while polymeric additives were needed to resist splintering for the tape heat set at 240 C. Calorimetry showed no difference in heat-of-fusion implying identical crystallinity in the tapes heat set at 140 C and 240 C. However, X-ray studies revealed that the crystallites in the tape heat set at 140 C were smaller/and or imperfect, and hence there were more lateral tie-molecules that provided it the splitting resistance. Pure PET tape if heat set below 150 C may be a workable solution for weaving, thereby dispensing with the need for toughening additives.