SYNOPSISSeveral samples of poly(1actic acid) with different molecular weights and tacticity have been prepared, and some PLLA injection moulded specimens have been annealed to promote their crystallization. From the characterization data, poly(L-lactide) showed more interesting mechanical properties than poly(D,L-lactide), and its behavior significantly improves wit.h crystallization. In fact, annealed specimens possess higher values of tensional and flexural modulus of elasticity, Izod impact strength, and heat resistance. The plateau region of flexural strength as a function of molecular weights appears around Mu = 35,000 for PDLLA and amorphous PLLA and at higher molecular weight, around Mu = 55,000, for crystalline PLLA. The study of temperature effect shows that a t 56°C only crystalline PLLA still exhibits useful mechanical properties. 0 1996 John Wiley & Sons, Inc.I NTRODU CTI 0 N Scientific and industrial interest in lactic acid polymers is increasing, not only for biomedical applications, but also for potential large-scale uses, such as packaging and many consumer goods.' In spite of the very good thermoplastic behavior of these materials, the relatively high cost of the intermediate lactide deeply affects the possibility of their commercialization 2-4 : an intensive purification, based on several crystallizations, is in fact generally required for reaching high-molecular-weight polymers and, consequently, useful mechanical properties. In this context, the industrial manufacturing of lactic acid polymers for high volume production should be oriented by evaluating the correlations between molecular weight and characteristics of the material. Moreover, lactic acid crude polymers easily show a thermal degradation during melt processing, 5-7 with relevant reduction of molecular weight. This also affects the properties of these materials with unfavorable consequences in several application fields.The aim of this research was to investigate the * To whom correspondence should be addressed.Journal of Applied Polymer Science, Vol. 59,37-43 (1996) 0 1996 John Wiley & Sons, Inc.CCC 0021-8995/96/010037-07 correlation between molecular weight, of poly (L-lactide) (PLLA) and poly (D,L-lactide) (PDLLA) and their mechanical properties. We decided to characterize medium-and low-molecular-weight samples since they can be obtained from monomers having received less purification steps and because they can derive from the degradation of higher molecular weight materials. The polymers were synthesized by ring opening polymerization of L-and D,L-lactide with S n (11) 2-ethylhexanoate (stannous octoate) , iats described in a previous paper8 and generally in the chemical literature.'-" We decided to prepare lower molecular weight samples by extruding the polymers several times without any purification or stabilization step. I t is well known that in these conditions lactic acid polymers exhibit a fast degradati01-1,~'~ especially if it is associated with hydrolitic phenomena.Besides mechanical testing the injection moulded sp...

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Bioplastics from renewable origin are a new generation of plastics able to significantly reduce the environmental impact in terms of energy consumption and green‐house ef‐fect in specific applications. Bioplastics perform as traditional plastics when in use and are completely biodegradable within a composting cycle. Today bioplastics and partic‐ularly starch‐based plastics are used in specific industrial applications where bio‐degradability is required. Examples are composting bags and sacks, fast food service‐ware (cups, cutlery, plates, straws, etc.), packaging (soluble foams for industrial pack‐aging, film wrapping, laminated paper, food containers), agriculture (much films, nur‐sery pots, plant labels), hygiene (diaper back sheet, cotton swabs).Moreover new sec‐tors are growing outside biodegradability, driven by improved technical performances of bioplastics versus traditional materials, as in the case of biofillers for tires. The market of starch‐based bioplastics in 1999 has been estimated at about 20,000 t/a, with a strong incidence of soluble foams for packaging and films. Bioplas‐tics from renewable origin, either biodegradable or non‐biodegradable, still constitute a niche market which requires high efforts in the areas of material and application devel‐opment; the technical and economical breakthroughs achieved in the last three years, however, open new possibilities for such products in the mass markets and specifical‐ly in food packaging. This paper will review the recent industrial achievements of bioplastics in the sector of packaging, taking in consideration their in‐use performances, biodegradation behav‐iour and environmental impact.

Introduction Historical Outline Methodology of LCA Presentation of Comparative Data Starch Polymers Polyhydroxyalkanoates (PHA) Polylactides (PLA) Other Polymers based on Renewable Resources Natural Fiber Composites Summarizing Comparison Discussion Conclusions Summary and Further Elaboration of Findings Outlook and Perspectives Acknowledgments

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Biodegradable polymers constitute a loosely defined family of polymers that are designed to degrade through the action of living organisms. They offer a possible alternative to traditional nonbiodegradable polymers if recycling is impractical or not economical. The main driving force behind this technology is the solid waste problem, particularly with regard to the decreasing availability of landfills, the litter problem and the pollution of marine environment by non‐biodegradable plastics. Technologies like composting used for the disposal of food and yard waste are the most suitable for the disposal of biodegradable materials. European Standardisation Committee (CEN), Organic Reclamation and Composting Association (ORCA) and German Institute for Standardisation (DIN) have already defined, at a draft level, the basic requirements for a product to be declared compostable. They are based on: complete biodegradability of the product in a time period compatible with composting, measured through respirometric tests (ASTM D5338‐9, ISO/CD14855, etc); disintegration of the material during the fermentation phase; no negative effects on compost quality; checking of laboratory‐scale results on pilot/full‐scale composting plants. These requirements set forth a common base for a universal marking system to readily identify products to be composted. Thermoplastic starch‐based polymers and aliphatic polyesters are the two classes of biodegradable materials with the greatest near‐term potential. This paper reviews a great variety of properties, structures and biodegradation behaviour of thermoplastic starch in combination with poly(vinyl alcohol) or some aliphatic polyesters like poly(hydroxybutyrate‐co‐hydroxyvalerate), poly(lactic acid), poly(ϵ‐caprolactone) and poly(butanediyl succinate).

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