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.