Biodegradable polymers articles

Compared with tar, which has a relatively short lifetime in the marine environment, the residence times of plastic, glass and non-corrodible metallic debris are indefinite. Most plastic articles are fabricated from polyethylene, polystyrene or polyvinyl chloride. With molecular weights ranging to over 500,000, the only chemical reactivity of these polymers is derived from any residual unsaturation and, therefore, they are essentially inert chemically and photochemically. Further, since indigenous microflora lack the enzyme systems necessary to degrade most of these polymers, articles manufactured from them are highly resistant or virtually immune to biodegradation. That is, the properties that render plastics so durable... 

Biocides are naturally toxic to lower organisms and therefore must be handled with care. Strict government rules control the sale and use of biocides, especially those used in food contact applications. They are added at the fabrication stage. The morphology of the polymer article is important, e.g., high surface area articles, such as foams, biodegrade more rapidly. 

Extrusion is a continuous conversion process via melting and subsequent transformation of granules or powders of biodegradable polymers and additives into semifinished or finished articles like sheets, profiles, tubes, bottles, films, tapes or... 

Several review articles on biodegradable polymers and polyesters have appeared in the literature [12-22]. Extensive studies have been carried out by Al-bertsson and coworkers developing biodegradable polymers such as polyesters, polyanhydrides, polycarbonates, etc., and relating the structure and properties of aliphatic polyesters prepared by ROP and polycondensation techniques. In the present paper, the current status of aliphatic polyesters and copolyesters (block, random, and star-shaped), their synthesis and characterization, properties, degradation, and applications are described. Emphasis is placed primarily on aliphatic polyesters derived by condensation of diols with dicarboxylic acids (or their derivatives) or by the ROP of cyclic monoesters. Polyesters derived from cyclic diesters or microbial polyesters are beyond the scope of this review. 

In view of the necessity for getting waste disposal under control coupled with the limited fossil raw material resources, biodegradable polymer and in particular polymers from renewable resources will gain importance in the future. In the most sensitive application area, food contact materials and articles, it is possible initially to use these materials in very limited amounts. The easy decomposition of these packaging materials is in opposition with the inertness needed to protect packaged food. These polymers are particularly sensitive to moisture. By finishing operations such as surface treatments, one could improve the inertness of these polymers. However, the degradability would be diminished by such processes. 

Most biodegradable polymers can be used for making injection moulded articles. Starch-based polymers are used to manufacture a wide range of items such as pencil sharpeners, rulers, cartridges, combs and toys, plant pots and bones. 

In terms of biodegradable polymers, PLA is finding growing use for manufacture of thermoformed articles such as single-use disposable cups and trays, particularly for outdoor events. Starch-based biodegradable polymers can also be thermoformed for production of trays and containers for packaging fresh food and convenience food. 

In this chapter, solid-state structure and properties relative to the morphologies of several chemically and bacterially synthesized biodegradable polymeric materials are described based mainly on the results obtained for bacterially synthesized polyesters by high resolution solid-state NMR spectroscopy. This chapter briefly discusses polymer blends, which also includes polysaccharides and proteins, since more details are given in other chapters of this book. Several books on biodegradable polymers have been published [1,2], and many review articles on structure and properties of bacterially synthesized polyesters have also been published elsewhere [7-10, 19-22]. 

This article provides a review of thermoplastic starch polymers [unlike polymers with added granular starch] including an introduction to biodegradable polymers and thermoplastic starch polymers a review of thermoplastic starch polymer development a review of reactive modification of thermoplastic starch, examining the structure-property relationships of thermoplastic starch and a review of commercial thermoplastic starch polymer applications. 

The present volume comprises five review articles written especially for this series by leading authorities in the field. The first three adresses major structural characteristics of biodegradable polymers. Robert Lenz provides athorough review of biodegradable polymers. Jorge Heller offers a critical analysis of the structure, properties and medical applications of polyorthoesters, whereas Abraham Domb and his associates offer the same critical analysis of polyanhydrides. Eric Doelker discusses the structure and properties of cellulose derivatives. Finally Michael Sefton presents the use of polyacrylates for the microencapsulation of live animal cells. 

In this article, the various biomaterials described have, in general, been considered separately. However, the use of biodegradable polymers in tissue engineering and the fabrication of hydrogels by self-assembly suggest that future developments in biomaterials research may benefit from an increasingly integrated approach. 

Natural polymers such as starch and protein are potential alternatives to petroleum-based polymers for a number of applications. Unfortunately, their high solubility in water limit their use for water sensitive applications. To solve this problem thermoplastic starches have been laminated using water-resistant, biodegradable polymers. For example, polylactic acid and P(3HB-co-3HV) were utilised as the outer layers of the stratified polyester/PWS (plasticized wheat starch)/polyester film strucmre in order to improve the mechanical properties and water resistance of PWS which made it useful for food packaging and disposable articles [65]. Moreover, improved physic-chemical interactions between P(3HB-CO-3HV) and wheat straw fibres were achieved with high temperature treatment. It resulted in increased P(3HB-co-3HV) crystallization, increased Young s moduli and lowered values of stress and strain to break than the neat matrix of P(3HB-co-3HV). There was no difference in the biodegradation rate of the polymer [66]. 

The hydrolytic degradation of PLAs and copolymers has been intensively studied, and, as a result, there are more than 250 papers related to this issue [188,189]. The degradation mechanism, behaviour, and rate depend on material- and media-related factors, which are summarized in Table 8.3. In addition, the methods used to monitor the hydrolytic degradation of biodegradable polymers are summarized in Table 8.4. Detailed information regarding the hydrolytic degradation of PLA-based materials can be found in the related review articles [188-190],... 

A few commercially available biodegradable polymer-based articles. 

The simplest and most effective way to improve the properties is to combine soy protein with a biodegradable polymer to form soy based biopol mers. The other method is to use functional monomers or oligomers to modify the soy protein during the processing of soy protein with an extruder. Casting methods or pretreatment methods with soy protein to form articles for applications can be used. 

The biodegradable polymers have high compatibility with microbial cells so that articles molded or otherwise formed from the biodegradable pol5mers can be easily decomposed by activated sludge or under conditions buried in the ground (41). 

Several binder fibers have been developed that are biodegradable to enhance the disposability of the absorbent article. Most often, biodegradable polymers are formed from aliphatic polyester materials. A multicomponent fiber that contains a high melting aliphatic polyester and a low-melting aliphatic polyester has been developed (25). 

Blends of styrenic pol5m ers (PS, high impact poly (styrene)) and biodegradable polymers (PLA) can be extruded and thermo-formed to produce very low density food service and consumer foam articles (29,31). The blends are compatibilized with styrene-based copolymers a styrene-maleic anhydride copol5mier, or a styrene methyl methacrylate copolymer. As blowing agent for foaming the compositions z-pentane is used. 

Biodegradable polymers or bioplastics are extensively used in packaging, gardening, or for disposable catering articles. In 1966 Kulkami et al. reported the biodegradability of polylactic acid (PLA) in the human body [18]. Due to their long-term degradability, bioplastics are under extensive research for biomedical applications. Particular focus was put on PLA as it is used as a feedstock in 3D printers. Therefore, it was seen as... 

---