Wrinkling in polymer film‐polymer substrate systems and a technique to minimize these surface distortions

Abstract

Thermally induced wrinkling during thermoforming of a commercial multi-layered polymer film/substrate laminate has been reported. The differential thermal expansion of component layers coupled with phase transition of the substrate with increasing temperature, determined the critical conditions for wrinkling with a specific wavelength and amplitude. An effective technique to minimize wrinkling by biaxially stretching the samples at high temperature before the forming operation, has been proposed. The samples were biaxially stretched by inflating the samples using a specially designed blowing unit retrofitted to a conventional vacuum thermoformer. This method involved heating, inflation and forming, together to provide stretch-assisted thermoforming. During biaxial stretching the stored compressive stresses in a wrinkled sample were relieved before the forming step, producing a decorative part without losses in surface appearance.

Melt rheological properties of PBT/SEBS and reactively compatibilized PBT/SEBS/SEBS‐g‐MA polymer blends

“…The power law indices are marginally lower than the PBT/SEBS blends at corresponding Φ d and temperature values which may be due to a partial plasticizing function by the low molecular weight SEBS‐ g ‐MA fraction produced during MA grafting or degradation of the later during processing. The K values are significantly higher than those in the uncompatibilized blends which may be due to enhanced phase adhesion as was also observed in other works …”

“…The variations were linear in the shear rate range studied (100–5000 s −1 ). The shear stress increases with Ф d and also with shear rate which indicates that the blends followed power law behavior similar to other filled polymer and blend systems . As SEBS concentration increased, the flow curves moved upward.…”

“…A network type of structure can form which enhances the friction for the polymer melt flow. In other systems also, phase interaction was observed to enhance the melt viscosity …”

“…In other systems also, phase interaction was observed to enhance the melt viscosity. 27,29 With increase in shear rate the compatibilized blends also exhibited decrease in g a and beyond 3500 s 21 the curves tend to converge implying marginal effect of phase interaction at high viscous forces, Figure 5. It implies that reactive compatibilization decreases interfacial slip in PBT/SEBS/SEBS-g-MA blend systems.…”

“…The shear stress increases with A d and also with shear rate which indicates that the blends followed power law behavior similar to other filled polymer and blend systems. 27 As SEBS concentration increased, the flow curves moved upward. This means that at a constant shear rate a system with high SEBS concentration shows higher shear stress than a blend with low SEBS content.…”