Abstract
The massive use of synthetic plastics, in particular in the food packaging area, has a great environmental impact, and alternative more ecologic materials are being required. Poly(lactic) acid (PLA) and starch have been extensively studied as potential replacements for non-degradable petrochemical polymers on the basis of their availability, adequate food contact properties and competitive cost. Nevertheless, both polymers exhibit some drawbacks for packaging uses and need to be adapted to the food packaging requirements. Starch, in particular, is very water sensitive and its film properties are heavily dependent on the moisture content, exhibiting relatively low mechanical resistance. PLA films are very brittle and offer low resistance to oxygen permeation. Their combination as blend or multilayer films could provide properties that are more adequate for packaging purposes on the basis of their complementary characteristics. The main characteristics of PLA and starch in terms of not only the barrier and mechanical properties of their films but also of their combinations, by using blending or multilayer strategies, have been analyzed, identifying components or processes that favor the polymer compatibility and the good performance of the combined materials. The properties of some blends/combinations have been discussed in comparison with those of pure polymer films.
Highlights
Over the last few decades, the environment has become one of the major global concerns, especially in the face of pollution, the depletion of natural resources and environmental degradation.As a consequence, research efforts have been developed at different levels to find alternative solutions.A specific concern is the field of packaging, which produces great amounts of non-degradable plastic waste accumulated in critical areas around the planet, causing severe problems and representing high recycling costs
Poly(lactic) acid (PLA) is a linear aliphatic thermoplastic polyester derived from lactic acid, which is obtained from the fermentation of 100% renewable and biodegradable plant sources, such as corn or rice starches and sugar feed stocks
Gelatinization can be carried out with an excess of water (>90% w/w) [54] in the case of films obtained by casting or it can be achieved at low moisture content during the thermal processing, by applying high-shear and high-pressure conditions; this is performed in the presence of plasticizers, such as water or glycerol, which tear down the starch granules, permitting a faster water transfer into the molecules and provoking the breakage of the amylopectin matrix, releasing the amylose
Summary
Over the last few decades, the environment has become one of the major global concerns, especially in the face of pollution, the depletion of natural resources and environmental degradation. Materials 2017, 10, 952 applications), strength, transparency, stability, permeability and ease of sterilization, all of which making them suitable for food packaging Despite their good properties, their use and accumulation imply serious environmental problems and dependence on fossil fuels. Poly(lactic) acid and starch have been extensively studied as potential replacers of non-degradable petrochemical polymers on the basis of their availability, adequate food contact properties and competitive cost. Both PLA and starch are semicrystalline polymers, and the crystallinity degree of their films depends both on the source and processing conditions. The properties of some blends/combinations will be discussed in comparison with those of pure polymer films
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