Polysaccharide-plastic blend

COLE Constmuits on Decay of Polysaccharide—Plastic Blends... 

COLE QfnstraiiUs on Deci of Polysaccharide-Plastic Blends... 

Oxygen Availability in Degrading Films. A major difference between natural materials and starch-plastic or cellulose-plastic blends is that the hydrophilic and relatively permeable matrix of materials like wood and hydrated polysaccharide films allows diffusion of O2 and release of nutrients from sites at a distance from the invasion site. As colonization proceeds, pore enlargement occurs when the pore walls are degraded (8) or as the polymer matrix of amylose or PVA films is hydrolyzed (10.12). In contrast, the LDPE matrix supplies no nutrients, hinders diffusion of water and O2, and the pore diameter cannot be increased. The consequence of impermeability is that the sole means of obtaining O2 and nutrients is by diffusion through water-filled pores. 

Blends of different polysaccharides and plasticizers are commonly used in pharmaceutical formulations, particularly those geared for controlled release. Due to its importance, the physical compatibility of these blends was examined by a number of investigators. Sakellariou and associates studied the... 

In order to preserve the final compostabihty, different blends of biodegradable materials have been developed. There is a vast body of literature available in this domain. We find certain associations with agropolymers such as proteins [ARV 99, FIS 00, OTA 99] or pectins [FIS 00], but most research focuses on blends of plasticized starches and biodegradable polyesters PCL, PHA, PBSA, PBAT, etc. These polyesters, described previously, are produced industrially. They exhibit interesting properties such as a more hydrophobic natiue, limited water permeability and improved mechanical properties, in comparison to polysaccharides. However, the cost of biodegradable polyesters is generally higher than that of starch... 

For hydrophilic compounds such as polysaccharides (thermoplastic starch) and proteins, multilayer structures provide certain advantages compared with polymer blends. For instance, moisture sensitivity of these hydrophilic polymers is not completely protected in blends because the phase distribution is close to the surface. However, starch or another hydrophilic film can be held between hydrophobic biodegradable components by using multilayers, thus avoiding the plasticization of the hydrophilic materials. 

Among the different categories of biodegradable plastics obtained from agropolymers, both starch/polyesters blends and microbial biodegradable plastics satisfied the majority of requirements asked by the plastic packaging industries (material qualities, processability, performances, etc.). Other bioplastics based on natural polysaccharides or proteins are mainly interesting for their low cost but their non-reproduetive quality and lower performances are still a handicap. 

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