Heat setting of stretched and microvoided PE/CaCO3 films

Calcium-carbonate-filled linear low-density polyethylene (LLDPE) films play an important role in the hygienics market because these materials allow fo r the diffusion of water vapor (breathability) and retain a liquid barrier while providing a barrier to liquids. This is achieved when properly formul ated composites are stretched to create pores. There are many important iss ues surrounding this technology; this report focuses on the effects of post stretching heat-set treatment on moisture vapor transmission rate (MVTR), d ynamical mechanical thermal analysis (DMTA), tensile heat distortion temper ature (THDT), and differential scanning calorimetry (DSC) thermal transitio ns of the porous film properties. Eastman personnel provided the LLDPE/CaCO 3 breathable films for this study. In general, the film properties were ins ensitive to heat-setting time beyond that of 1 min. This result suggests th at the molecular reorientation and recrystallization associated with the ch anges in film properties occur rapidly. Properties were, however, strongly sensitive to the heat-set temperature when MVTR decreased and DMTA properti es [specifically storage modulus (E ') and the alpha -transition temperatur e] increased as the heat-set temperature increased. This is believed to hav e been mainly caused by pore closure and the annealing of crystalline regio ns. The heat-set temperature was easily detectable by DSC techniques when a thermal transition was apparent at the applied temperature, and changes in the heat of fusion for the sample could be observed. Ultimately, the chang es in the properties of these porous films were related to changes in the m olecular orientation and crystallinity of the matrix in combination with ch anges in the void structure of the composite, In particular, changes in E ' could be related to these separate effects. (C) 2001 John Wiley & Sons, In c.