The use of plastic mulch in agriculture has increased dramatically in the last 10 years throughout the world. This increase is due to benefits such as increase in soil temperature, reduced weed pressure, moisture conservation, reduction of certain insect pests, higher crop yields, and more efficient use of soil nutrients. However, disposing of used plastic films, which cause pollution, has led to development of photodegradable and biodegradable mulches. Here we review the use of plastic mulches in agriculture, with special reference to biodegradable mulches. Major topics discussed are (1) history of plastic mulch and impact on crop yield and pest management, (2) limitations of polyethylene mulches and potential alternatives, (3) biodegradable and photodegradable plastic mulches, (4) field performance of biodegradable mulches, and (5) use of biodegradable plastic mulches in organic production. We found that (1) despite multiple benefits, removal and disposal of conventional polyethylene mulches remains a major agronomic, economic, and environmental constraint; (2) early use of photodegradable plastic mulch during the 1970s and 1980s, wrongly named biodegradable mulch films, discouraged adoption of new biodegradable mulch films because they were too expensive and their breakdown was unpredictable; (3) biodegradable plastic films are converted through microbial activity in the soil to carbon dioxide, water, and natural substances; (4) polymers such as poly(lactic acid), poly(butylene adipate-coterephthalate), poly(e-caprolactone), and starch-based polymer blends or copolymers can degrade when exposed to bioactive environments such as soil and compost; (5) with truly biodegradable materials obtained from petroleum and natural resources, opportunity for using biodegradable polymers as agricultural mulch films has become more viable; and (6) the source of polymer and additives may limit use of some biodegradable mulches in organic production. More knowledge is needed on the effect of biodegradable mulches on crop growth, microclimate modifications, soil biota, soil fertility, and yields.

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Polyethylene and biodegradable mulches for agricultural applications: a review

Thermal processing of starch-based polymers

Nanocomposite materials were obtained using glycerol plasticized starch as the matrix and a colloidal suspension of cellulose whiskers as the reinforcing phase. The cellulose whiskers, prepared from tunicin, consisted of slender parallelepiped rods with a high aspect ratio. After mixing the raw materials and gelatinization of starch, the resulting suspension was cast and evaporated under vacuum. The composites were conditioned at various moisture contents in order to evaluate the effect of this parameter on the composite structure. The resulting films were characterized using scanning electron microscopy, differential scanning calorimetry, water absorption experiments, and wide-angle X-ray scattering. An accumulation of plasticizer in the cellulose/amylopectin interfacial zones was evidenced. The specific behavior of amylopectin chains located near the interface in the presence of cellulose probably led to a transcrystallization phenomenon of amylopectin on cellulose whiskers surface.

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Plasticized Starch/Tunicin Whiskers Nanocomposites. 1. Structural Analysis

Oils, and Polysaccharides Alessandro Gandini,*,†,‡ Talita M. Lacerda,†,‡ Antonio J. F. Carvalho,‡ and Eliane Trovatti†,‡ †Saõ Carlos Institute of Chemistry, University of Saõ Paulo, Avenida Trabalhador Saõ-carlense 400, CEP 13566-590, Saõ Carlos, Saõ Paulo, Brazil ‡Department of Materials Engineering, Saõ Carlos School of Engineering, University of Saõ Paulo, Avenida Joaõ Dagnone 1100, CEP 13563-120, Saõ Carlos, Saõ Paulo, Brazil

Progress of Polymers from Renewable Resources: Furans, Vegetable Oils, and Polysaccharides

Over the coming few decades bioplastic materials are expected to complement and gradually replace some of the fossil oil based materials. Multidisciplinary research efforts have generated a significant level of technical and commercial success towards these bio-based materials. However, extensive application of these bio-based plastics is still challenged by one or more of their possible inherent limitations, such as poor processability, brittleness, hydrophilicity, poor moisture and gas barrier, inferior compatibility, poor electrical, thermal and physical properties. The incorporation of additives such as plasticizers into the biopolymers is a common practice to improve these inherent limitations. Generally, plasticizers are added to both synthetic and bio-based polymeric materials to impart flexibility, improve toughness, and lower the glass transition temperature. This review introduces the most common bio-based plastics and provides an overview of recent advances in the selection and use of plasticizers, and their effect on the performance of these materials. In addition to plasticizers, we also present a perspective of other emerging techniques of improving the overall performance of bio-based plastics. Although a wide variety of bio-based plastics are under development, this review focuses on plasticizers utilized for the most extensively studied bioplastics including poly(lactic acid), polyhydroxyalkanoates, thermoplastic starch, proteinaceous plastics and cellulose acetates. The ongoing challenge and future potentials of plasticizers for bio-based plastics are also discussed.

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Progress in bio-based plastics and plasticizing modifications

Amelioration de la formulation de paillages plastiques biodegradables par addition d'urees et de polyols a des melanges amidon-copolymeres d'acide acrylique et d'ethylene

Starch-based blown films. 2

Biodegradable film compositions which will withstand outdoor exposure for a desired time and then disintegrate are prepared from starch and ethylene acrylic acid copolymers. These film compositions are useful for agricultural mulch and heat-sealable packaging.

Biodegradable film compositions prepared from starch and copolymers of ethylene and acrylic acid

Biodegradable Films from Starch and Ethylene-Acrylic Acid Copolymer

Film-forming formulations comprising starch, ethylene acrylic acid copolymer, and optionally polyethylene, can be blown into films upon neutralization of a portion of the copolymer acid functionality. The resultant biodegradable films have potential application as agricultural mulch, garbage bags, and various types of packaging.

Biodegradable starch-based blown films

Semipermeable films useful as dialysis membranes are prepared from starch-based composites. The films are shaped by conventional methods from a plasticized matrix comprising highly gelatinized starch and ethylene acrylic acid copolymer neutralized with a strong alkali. These films are remarkably transparent and resistant to degradation in the presence of aqueous solutions.

Richard P. Westhoff

Papers

Starch-based blown films. 2

Biodegradable film compositions prepared from starch and copolymers of ethylene and acrylic acid

Biodegradable Films from Starch and Ethylene-Acrylic Acid Copolymer

Biodegradable starch-based blown films

Starch-base semipermeable films