Additives in Biopolymers, Analysis by Chromatographic Techniques

ROXANA A. RUSECKAITE; ALFONSO JIMÉNEZ

Encyclopedia of Chromatography 2 Edition

Marcel Dekker Eds

Lugar: New York; Año: 2005; p. 8 - 12

Biopolymers are naturally occurring polymers that are formed in nature during the growth cycles of all organisms; they are also referred to as natural polymers.(1) Their synthesis generally involves enzyme-catalyzed, chain growth polymerization reactions, typically performed within cells by metabolic processes. Biodegradable polymers can be processed into useful plastic materials and used to supplement blends of the synthetic and microbial polymer.(2) Among the polysaccharides, cellulose and starch have been the most extensively used. Cellulose represents an appreciable fraction of the waste products. The main source of cellulose is wood, but it can also be obtained from agricultural resources. Cellulose is used worldwide in the paper industry, and as a raw material to prepare a large variety of cellulose derivatives. Among all the cellulose derivatives, esters and ethers are the most important, mainly cellulose acetate, which is the most abundantly produced cellulose ester. They are usually applied as films (packaging), fibers (textile fibers, cigarette filters), and plastic molding compounds. Citric esters (triethyl and acetyl triethyl acetate) were recently introduced as biodegradable plasticizers in order to improve the rheological response of cellulose acetate. Starch is an enormous source of biomass and most applications are based on this natural polymer. It has a semicrystalline structure in which their native granules are either destroyed or reorganized. Water and, recently, low-molecular-weight polyols,(2) are frequently used to produce thermoplastic starches. Starch can be directly used as a biodegradable plastic for film production because of the increasing prices and decreasing availability of conventional film-forming materials. Starch can be incorporated into plastics as thermoplastic starch or in its granular form. Recently, starch has been used in various formulations based on biodegradable synthetic polymers in order to obtain totally biodegradable materials. Thermoplastic and granular starch was blended with polycaprolactone (PCL),(3) polyvinyl alcohol and its co polymers, and polyhydroxyalcanoates (PHAs).(4) Many of these materials are commercially available, e.g., Ecostar (polyethylene/starch/unsaturated fatty acids), Mater Bi Z (PCL/starch/natural additives) and Mater Bi Y (polyvinylalchol-co-ethylene/starch/natural additives). Natural additives are mainly polyols. The proteins, which have found many applications, are, for the most part, neither soluble nor fusible without degradation. Therefore, they are used in the form in which they are found in nature.(1) Gelatin, an animal protein, is a water-soluble and biodegradable polymer that is extensively used in industrial, pharmaceutical, and biomedical applications.(2) A method to develop flexible gelatin films is by adding polyglycerols. Quite recently, gelatin was blended with poly(vinyl alcohol) and sugar cane bagasse in order to obtain films that can undergo biodegradation in soil. The results demonstrated the potential use of such films as self-fertilizing mulches.(5) Other kinds of natural polymers, which are produced by a wide variety of bacteria as intracellular reserve material, are receiving increasing scientific and industrial attention, for possible applications as melt processable polymers. The members of this family of thermoplastic biopolymers are the PHAs. Poly(3-hydroxy)butyrate (PHB), and poly(3-hydroxy)butyrate-hydroxyvalerate (PHBV) copolymers, which are microbial polyesters exhibiting useful mechanical properties, present the advantages of biodegradability and biocompatibility over other thermoplastics. Poly(3-hydroxy)butyrate has been blended with a variety of low- and high-cost polymers in order to apply PHB-based blends in packaging materials or agricultural foils. Blends with nonbiodegradable polymers, including PVAc, PVC, and PMMA, are reported in the literature.(4) Poly(3-hydroxy)butyrate has been also blended with synthetic biodegradable polyesters, such as poly(lactic acid) (PLA), poly(caprolactone), and natural polymers including cellulose and starch.(2) Plasticizers are also included into the formulations in order to prevent degradation of the polymer during processing. Polyethylene glycol, oxypropylated glycerol, dibutylsebacate (DBS), dioctylsebacate (DOS), and polyisobutylene (PIB) are commonly used as PHB plasticizers.(6) As was pointed out above, the processing and in-use biopolymer properties depend on the addition of other materials that provide a more convenient processing regime and stabilizing effects. Therefore the identification and further determination of these additives, as well as the separation from the biopolymer matrix, is necessary, and chromatographic techniques are a powerful tool to achieve this goal.Many different compounds can be used as biopolymer additives, most of them are quite similar to those used in traditional polymer formulations. The use of various compounds as plasticizers, lubricants, and antioxidants has been recently reported.(7-9) Antioxidants are normally used to avoid, or at least minimize, oxidation reactions, which normally lead to degradation and general loss of desirable properties. Phenol derivatives are mostly used in polymers, but vitamin E and -tocopherols are those most commonly found in biopolymer formulation.(10)