Transparency of polymer blends

Abstract

Polymer blending is useful for improving physical properties. Blends of transparent polymers are generally hazy. However, transparency is required in many products such as packages (especially PET bottles). The miscible blends, PET (polyethylene terephthalate)/PBT (polybuthylene terephthalate), maintain transparency in almost all cases regardless of the blending ratio, whereas the immiscible blends, PET/MxNYLON (MXD6 nylon, i.e. polymethaxylirene adipamide) and PET/PMAI (polymethacril imide, i.e. N‐methyl dimethyl glutarimide) become hazy as the blending ratio increases. The reason for this haze is the number and size of the dispersed particles. Differences in the refractive indices of various polymers also have a large influence on haze. Stretching makes even the transparent blends hazy in the case of PET/MxNYLON. One reason for this phenomenon is that stretching increases the size of the dispersed particles in the sheet plane. A second reason is that the difference in the anisotropic refractive indices of the matrix and the dispersed phase is increased by stretching. These effects are very consistent with light scattering theory.

When medical evidence alone is simply not enough

“…The authors found that the O 2 permeability at 43% relative humidity was reduced by a factor of 3, in comparison of PET, in the biaxially oriented film of the compatibilized blends. Compatibilized blends were also obtained using ionomers 41. The goal of the studies on the PET/MXD6 blends is to achieve the improved gas barrier, while maintaining good optical clarity, inducing the interchange reaction between PET and MXD6 to produce in situ their copolymers and, thus to overcome their incompatibility.…”

Nylon-MXD6 resins for food packaging

“…For instance, in PET/Nylon-MXD6 blends haze was found to increase as the level of Nylon-MXD6 increased. 16 Stretching was also found to increase haze in the immiscible blends. Refractive index mismatch and particle size effects were identified as the contributing factors.…”

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].…”

“…Many polymers used in packaging applications are highly transparent, including polyethylene terephthalate, polycarbonate, polystyrene, etc. In fact, transparency is one of the most important characteristics of these polymers [1]. Polymer blends or compositions are widely used because of their ease of preparation and tailorable properties.…”