Properties of Biodegradable Multilayer Films Based on Plasticized Wheat Starch
| Main Authors: | , , , |
|---|---|
| Format: | Article |
| Language: | English Slovak |
| ISSN: | ISSN 0038-9056 |
| Online Access: | http://www.viks.sk/chk/star_8_01_372_380.doc |
| Abstract: | Summaries. ilayer films based on plasticized wheat starch (PWS) and various biodegradable aliphatic polyesters have been prepared through flat film coextrusion and compression molding. Poly(lactic acid) (PLA), polyesteramide (PEA), poly(e-caprolactone) (PCL), poly(butylene succinate adipate) (PBSA), and poly(hydroxybutyrate-co-valerate) (PHBV) were chosen as the outer layers of the stratified "polyester/PWS/polyester" film structure. The main goal of the polyester layers was to improve significantly the properties of PWS in terms of mechanical performance and moisture resistance. Since no specific compatibilizer or tie layer were added, the properties of subsequent films rely on the compatibility between the respective materials only. The effects of glycerol content in PWS, polyester type, and film composition on the mechanical properties and adhesion strength of multilayers were investigated. The conditions for optimal product performance were examined. The multilayer films may be suitable for applications in food packaging or disposable articles. Conclusions. Developing compostable and low-cost multilayer materials based on plasticized starch and biodegradable polyesters is interesting in more than one sense. One prerequisite in the preparation of multilayered products based on starch is to obtain sufficient adhesion between layers, moisture barrier properties and uniform layer thickness distribution. Two different techniques were used to prepared multilayers, i.e., coextrusion and compression molding. Different levels of peel strength were found, depending on the compatibility of plasticized starch with the respective polyesters. In particular, polyesteramide presented the best adhesion to the PWS layer, probably thanks to its polar amide groups (see Fig. 3). The PCL and PBSA showed medium adhesion values, and PLA or PHBV were the least compatible polyesters. The same trend in the magnitude of adhesion strength was observed between coextruded and hot pressed multilayers. These results are in good agreement with previous findings on starch-polyester blends [6-9] or laminates [13], and on surface energy properties [22]. We also observed the gradual decrease of peel strength values as the glyc-erol content in PWS was increased. It was possible to increase the adhesion properties of the film by up to 50%, by introducing polyesters blends in the cap layer or PWS/polyester blends in the central layer. Finally, the polyester cap layer slightly improved the mechanical properties of plasticized starch, especially for the low-modulus PWS type. It was also checked that the multilayers have satisfactory water resistance properties. This work allowed to validate the use of the coextrusion technique to prepare compostable multilayer films based on plasticized starch. However, some inherent problems exist due to the multilayer flow conditions encountered in coextrusion, such as encapsulation and interfacial instabilities phenomena. Addressing these problems is a crucial issue because they can be detrimental to the product, affecting the quality and functionality. Such investigations are currently underway in our laboratory. |
|---|---|
| ISSN: | ISSN 0038-9056 |
