Effect of machine direction orientation conditions on properties of HDPE films

Abstract

In this study, the effects of machine direction orientation (MDO) conditions on crystalline orientation, morphology, and mechanical performance of a high-density polyethylene film were investigated. The MDO variables studied were feed speed, stretching temperature, draw ratio (DR) as well as annealing temperature. The type of crystals (spherulites or fibrils) and crystallinity of the films were considered using differential scanning calorimetry. The MDO process increased the film crystallinity by 18% and melting temperature (T m ) by 5°C. The crystalline phase orientation was measured using Fourier transform infrared and wide angle X-ray diffraction. Stretching noticeably increased the crystalline alignment. The Young's modulus decreased with increasing extrusion temperature and feed speed and enhanced with rising annealing temperature. However, up to DR = 6, the Young's modulus decreased with draw ratio whereas it increased beyond DR = 6. Upon drawing, the tear resistance along the machine direction decreased significantly, but the puncture resistance along the normal direction increased drastically. Finally, drawing lowered haze for the films dramatically, hence, improved the clarity significantly. © 2009 The Author(s).