Other compostable polymers from renewable resources

OTHER COMPOSTABLE POLYMERS FROM RENEWABLE RESOURCES 2.2,1 Cellulose 

Cellulose, the most abundant organic compound on earth, is the major structural component of the cell wall of higher plants [15], It is major component of cotton (95%), flax (80%), jute (60-70%) and wood (40-50%). Cellulose pulps can be obtained from maity agricultural byproducts such as sugarcane, sorghum bagasse, com stalks, and straws of rye, wheat, oats, and rice. 

Cellulose is a pofydisperse linear pofysaccharide consisting of P-l,4-gfycosidic linked D-glucose units (so-called anhydroglucose unit) (see Fig. 2.13). 

The consequence of the supra-molecular stmcture of cellulose is its insolubility in water, as well as in common organic liquids [15, 21]. Poor solubility in conunon solvents is one of the reasons why cellulose is converted to its cellulose esters. Another reason is that eellulose is not 

Cellulose esters have been commercially important polymers for nearly a century, and have found a variety of applications, including solvent-borne coatings, separation, medical and controlled release applications as well as composites and laminates and plastics. 

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Other compostable polymers from renewable resources... 

Sustainability has many definitions. One way to think of it is meeting the needs of the present without compromising the ability of future generations to meet their needs (defined by the World Commission on Environment and Development held by the United Nations in 1983). The concept of sustainability is that we should synchronize our consumption of natural resources with the Earth s production - in other words, using up natural resources at the same rate at which they are produced. Compared to traditional polymers typically made from petroleum and other fossil resources such as natural gas, sustainable polymers are fuUy or partially biobased and/or biodegradable or compostable. They are bioplastics made from renewable resources (biomass) and can be broken down faster than traditional plastics. Sustainable polymers could also protect our Earth by offering a reduced carbon footprint, a reduced use of fossil resources, and improved end-of-life options. 

Poly(lactic acid) (PL A) is a renewable resource-based bioplastic with many advantages, compared to other synthetic polymers. PL A is eco-friendly, because, apart from being derived from renewable resources such as corn, wheat, or rice, it is recyclable and compostable [1, 2]. PLA is biocompatible, as it has been approved by the Food and Drug Administration (FDA) for direct contact with biological fluids [3] and has better thermal processability compared to other biopolymers such as poly(hydroxy alkanoate)s (PHAs), poly(ethylene glycol) (PEG), or poly(e-caprolactone) (PCL) [4]. Moreover, PLA requires 25-55% less energy to be produced than petroleum-based polymers, and estimations show that this can be further reduced by 10% [5]. 

Polymers based on lactic acid (PLA) are a most promising category of polymers made from renewable resources. They are not only compostable and biocompatible, but also pro-cessable with most standard processing equipment. The properties of lactic acid based polymers vary to a large extent depending on the ratio between, and the distribution of, the two stereoisomers or other comonomers [ 1-3]. The polymers can be manufactured by different polymerization routes, which are schematically described below (Figure 3.1). 

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