Poly from renewable sources

Chemical Industries are represented by BASF SE, Showa Denko, WACKER and DOW Chemicals, who are best qualified to present challenges and requirements of biodegradable polymers on an industrial scale. Information on mineral oil-based polyesters, poly(vinylalcohol), poly(butylenesuccinate), and new developments in the field of poly(urethanes) from renewable sources can be found within this volume. 

Polyesters are typically produced by step growth and ROP. In this chapter the different synthesis routes are discussed with reference to poly(lactic acid) (PLA), the most popular polymer made from renewable sources. However, the treatment is similarly applicable to the other a-esters already mentioned. 

Recently, biogradable and renewably derived polymers have attracted much attention due to the environmental concerns and sustainability issues associated with petroleum-based polymers. Such a polymer is poly (lactic acid) (PLA), a biodegradable and bioabsorbable, renewably derived thermoplastic polyester extensively investigated over the lastest several decades. PLA is a compostable polymer derived from renewable sources. 

The industrial exploitation of products from renewable sources and the design of new bioactive and biocompatible polymers capable of exerting a temporary therapeutic function are two diverse research areas currently considered to be strategic by the international scientific community. In the field of biocompatible polymers, poly(2-hydroxyethyl methacrylate) (PHEMA) and polysaccharides are among the most popular and widely investigated. 

The commercial forms of PLA are the homopolymer poly(L-Lactide) (L-PLA or PLLA) and the copolymer poly(D,L-Lactide) (D,L-PLA or PDLLA), which are produced from L-lactide and D,L-lactide, respectively. The L-isomer constitutes the main fraction of PLA derived from renewable sources, since the majority of lactic acid from biological sources exists in this form [43]. Polylactides (PLAs) exhibit different properties depending on the D/L unit radio and sequence distribution. Generally, the crystallinity of PLLA and PDLA decreases with increasing racemic content. PLA polymers with an L-content >90% tend to be semicrystalline, while those with a lower optical purity are generally amorphous [43-45]. 

The monomers used in the polycondensation reaction for the production of poly(alkylene dicarboxylate)s are basically from petrochemical sources. However, some of them can be obtained from renewable sources. For example, 1,3-propanediol can be produced by fermentation of glycerol, which is a by-product from biodiesel or plant oil production. Succinic acid can be synthesized from glucose or whey by bacterial fermentation in very high yields. ... 

Analogous poly(itaconate)s polymers like poly(ditetrahydrofurfuryl methacrylate) have been also studied because there are at least two advantages in using ita-conate acid based polymers over methacrylate acid derivatives itaconic acid can be obtained through fermentation from renewable, non petrochemical sources and the toxicity of its derivatives is lower than for methacrylate derivatives [64,140],... 

The newly inserted group of synthetic fibres based on renewable sources is just beginning, with poly-lactic fibres (PLA) as the prominent representative. One may also consider that, due to the move away from petrol sources, this group will become increasingly interesting in the coming decades. 

This chapter gives a general introduction to the book and describes briefly the context for which the editors established its contents and explains why certain topics were excluded from it. It covers the main raw materials based on vegetable resources, namely (i) wood and its main components cellulose, lignin, hemicelluloses, tannins, rosins and terpenes, as well as species-speciflc constituents, like natural rubber and suberin and (ii) annual plants as sources of starch, vegetable oils, hemicelluloses, mono and disaccharides and algae. Then, the main animal biomass constituents are briefly described, with particular emphasis on chitin, chitosan, proteins and cellulose whiskers from molluscs. Finally, bacterial polymers such as poly(hydroxyalkanoates) and bacterial cellulose are evoked. For each relevant renewable source, this survey alerts the reader to the corresponding chapter in the book. 

Most types of Hot melt adhesives used in the mannfacture of laminates and in rapid Packaging industry applications are mineral oil-derived, hydrophobic and essentially non-dispersible, so they cannot be considered as renewable. However, some basic polymers have been prepared over the last decade from vegetable sources, which are renewable, and are adhesive, although these properties have limitations. These include poly(hydro-xybutyrate/hydroxyvalerate) (PHBV), poly(lactide) (which has poor thermal stability), and starch esters. Adhesives based on sulphonated polyesters with polar petroleum waxes have improved adhesion and adequate water dispersibility. In general, however, the perfect adhesive from renewable resources with satisfactory adhesion properties remains to be discovered. 

Poly(lactic acid) (PLA) is a thermoplastic polyester characterized by mechanical and optical properties similar to polystyrene (PS) and polyethylene terephthalate (PET). It is obtained from natural sources, completely biodegradable and compostable in controlled conditions as already stated in previous chapters. PLA offers some key points with respect to classic synthetic polymers, since it is a bioresource and renewable, while raw materials are cheap and abundant compared to oil. From a commercial point of view, a non-secondaiy approach, it can embellish with the word green so fashioned for the major stream consumers. Legislation can also help the commercial diffusion of biopolymers. As an example, a decisive leap has been made with the control of non-biodegradable shopping bags distribution in the European Commission and many of its member states. In addition, PLA has received some interest from the industrial sectors because of its relatively low price and commercial availability compared with other bioplastics. This is the veiy key point for any successful polymer application. In fact, the current price of commercial PLA falls between 1.5 and 2 kg , which is sufficiently close to other polymers like polyolefins, polyesters or poly(vinyl chloride) (PVC). Clearly, the PLA market is still in its infancy, but it is expected that the decrease in the production costs and the improvement in product performance will result in a clear acceleration in the industrial interest for PLA uses. It is estimated that PLA consumption should reach... 

Bionanocomposites are an ecological alternative to conventional nanocomposites based on petroleum-derived polymers, as they are based on biodegradable polymers obtained from renewable resources. Biomass is the source of agropolymers like starch and cellulose and also of monomers used to chemically synthesize polymers like polylactic acid (PLA). Other kinds of biopolymers, e.g., xanthan gum and poly (hydroxyalkanoates), are produced by microorganisms. Even though most of the bionanocomposites reported in the hterature are based on layered sihcates, the number of examples illustrating the use of fibrous clays in the preparation of new bionanocomposites is growing rapidly. 

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