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

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 nano-indentation correlated with PET tapes that were, or were not, weavable. Nano-scratches 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 degrees C had a non-splintering character even without additives, while polymeric additives were needed to resist splintering for the tape heat set at 240 degrees C. Calorimetry showed no difference in heat-of-fusion implying identical crystallinity in the tapes heat set at 140 degrees C and 240 degrees C. However, X-ray studies revealed that the crystallites in the tape heat set at 140 degrees 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 degrees C may be a workable solution for weaving, thereby dispensing with the need for toughening additives.