Properties of wheat gluten/poly(lactic acid) laminates.
Laminates of compression-molded glycerol-plasticized wheat gluten (WG) films surrounded and supported by poly(lactic acid) (PLA) films have been produced and characterized. The objective was to obtain a fully renewable high gas barrier film with sufficient mechanical integrity to function in, for example, extrusion-coating paper/board applications. It was shown that the lamination made it possible to make films with a broad range of glycerol contents (0-30 wt %) with greater strength than single unsupported WG films. The low plasticizer contents yielded laminates with very good oxygen barrier properties. In addition, whereas the unsupported WG films had an immeasurably high water vapor transmission rate (WVTR), the laminate showed values that were finite and surprisingly, in several cases, also lower than that of PLA. Besides being a mechanical support (as evidenced by bending and tensile data) and a shield between the WG and surrounding moisture, the PLA layer also prevented the loss of the glycerol plasticizer from the WG layer. This was observed after the laminate had been aged on an "absorbing" blotting paper for up to 17 weeks. The interlayer adhesion (peel strength) decreased with decreasing glycerol content and increasing WG film molding temperature (130 degrees C instead of 110 degrees C). The latter effect was probably due to a higher protein aggregation, as revealed by infrared spectroscopy. The lamination temperature (110-140 degrees C) did not, however, have a major effect on the final peel strength.
Cho
Sung-Woo
SW
Fibre and Polymer Technology, Royal Institute of Technology, Stockholm, Sweden.
Gällstedt
Mikael
M
Hedenqvist
Mikael S
MS
D005983:Glutens / Q000737:chemistry*; D019344:Lactic Acid / Q000737:chemistry*; D055595:Mechanical Phenomena; D010968:Plasticizers / Q000737:chemistry*; D011091:Polyesters; D011108:Polymers / Q000737:chemistry*; D013696:Temperature; D014908:Triticum / Q000737:chemistry*
D010968:Plasticizers; D011091:Polyesters; D011108:Polymers; D019344:Lactic Acid; C033616:poly(lactide); D005983:Glutens