Improving the transparency of stretched poly(ethylene terephthalate)/polyamide blends

Abstract

Compatibilized blends of poly(ethylene terephthalate (PET) with an aromatic polyamide such as poly(m-xylylene adipamide) (MXD6) have good transparency (T) because the constituent refractive indices (RIs) match closely. However, haziness is observed when the blends are stretched. This study demonstrated that stretching imparted a greater RI anisotropy to PET than to the aromatic polyamide. The resulting RI mismatch was responsible for the loss in T. Analysis of the strain-dependent birefringence revealed that different molecular deformation models described the intrinsic birefringence of the PET and aromatic polyamides. Hydrogen bonding of the polyamide may have been responsible for the difference. On the basis of these results, three approaches for improving T of stretched PET blends were attempted. Blends with a lower molecular weight MXD6 exhibited slightly higher T after stretching; however, they did not compare with stretched PET. Increasing the amount of compatibilizer reduced the particle size; however, the dimension of even the smallest particles exceeded the quarter wavelength after biaxial stretching transformed the spherical particles into platelets. Copolyamides based on MXD6 that incorporated isophthalate were designed to increase the RI of the polyamide and thereby reduce the RI mismatch with stretched PET. Unexpectedly, the poor T of stretched copolyamide blends was attributed to the high glass-transition temperature of the copolyamide, which hampered the molecular orientation.

Commercial Polymer Blends

“…The addition of ca. 0.5 % mol% SIPA to the PET phase reduced the MXD6 particle size to 0.3 mm (Prattipati et al 2006;Ozen, et al 2010). It is known from earlier literature that sulfonated ionomers exhibit favorable interaction with nylons via a sulfonate anion-amide complexation mechanism (Feng et al 1996).…”

Improving gas barrier of PET by blending with aromatic polyamides

“…The melted blends were extruded through a 3 mm die, quenched in air and pelletized. The possibility of transamidation reaction between PET and MXD6 was eliminated by 13 C NMR analysis [15]. Blends were prepared with 5 and 10% by weight polyamide and 0, 15 and 30% by weight PET-co-SIPE.…”

“…Hindrance and inhibition of MXD6 crystallization were ascribed to fractionated crystallization behavior as a result of the small droplet size (100-300 nm) and strong interaction between SIPE and MXD6. A detailed analysis was presented previously [15].…”

“…Incorporating a small amount of sodium 5-sulfoisophthalate into the PET matrix effectively compatibilized PET blends with aromatic polyamides by reducing the polyamide particle size [15]. Sulfonated ionomers are known to interact strongly with aliphatic polyamides, establishing a network structure with sulfonate anions coordinated to amide N-H groups and counter ions complexed to multiple amide CaO groups [16].…”

Improving transparency of incompatible polymer blends by reactive compatibilization

“…The refractive index mismatch of polymer blends is transformed during stretching in the stretch and thickness directions. The mismatch is diminished in some cases but not in others [1,2]. The refractive index also changes with the temperature [3].…”