Starch with ethylene vinyl alcohol

Interesting products previously developed with the Mater-Bi technology include starch and ethylene-vinyl alcohol (EVOH) copolymers starch and PVA starch and aliphatic polyesters, in particular PCL. It is also possible to use aliphatic polyesters such as those formed by the reaction of glycols such as 1,4-BDO with succinic acid, sebacic acid, adipic acid, azelaic acid, dodecandioic acid or brassylic acid. 

Figure13.2 Substrates from blend of starch for 2 days (a) 10 min in O2 and applying a power with ethylene vinyl alcohol (SEVA) (50/50 wt%) of BOW (b) 30 min, O2 and power of SOW ...

On the other hand, the V complex formed by starch, having an amylose/amy-lopectin ratio higher than 20% by weight, with ethylene-vinyl alcohol (EVOH) copolymers makes even amylopectin insoluble in boiling water (Table 6.2). 

Graft copolymers of nylon, protein, cellulose, starch, copolymers, or vinyl alcohol have been prepared by the reaction of ethylene oxide with these polymers. Graft copolymers are also produced when styrene is polymerized by Lewis acids in the presence of poly-p-methoxystyrene. The Merrifield synthesis of polypeptides is also based on graft copolymers formed from chloromethaylated PS. Thus, the variety of graft copolymers is great. 

As an example the characterization of surface grafting onto an ethylene-vinyl alcohol (33 67) random copolymer (EVA) film33 is described here. Since this water-insoluble film has hydroxyl groups on the surface, surface grafting may occur, for instance, with the so-called dialdehyde starch (DAS), whose chemical structure is given by... 

Christian et al. [109] studied the oxygen permeability of MFC films at different relative humidity (RH). At low RH (0%), the MFC films showed very low oxygen permeabihty as compared with films prepared from plasticized starch, whey protein and arabinoxylan, and values in the same range as that of conventional synthetic films, e.g., ethylene vinyl alcohol. At higher RH s, the oxygen permeabihty increased exponentially, presumably due to the plasticizing and swelling of the carboxymethylated nanofibers... 

Other interesting articles and reviews include polyvinyl alcohol composites, generally [62], with proteins [63-65], starch [66], chitosan [67], simple sugars [68], and a Baeyer Villiger oxidation [95] (Scheme 3) of a an ethylene-vinyl alcohol copolymer to produce a biodegradable polyhydroxypolyester. 

Blends of com starch with poly(e- caprolactone), CA, PEA and ethylene-vinyl alcohol copolymer DSC and TGA Three degradation meehanisrrts were identified in the blends Mano et al. 2003... 

Marques et al. (2002) studied the biocompatibility of starch-based polymers. The materials used for this study were (i) a 50/50 (wt%) blend of cornstarch and ethylene vinyl alcohol (SEVA-C), (ii) SEVA-C reinforced with 30 % (wt) of hydroxyapatite, (iii) a 50/50 (wt%) blend of cornstarch and cellulose acetate (SCA), and (iv) SCA reinforced with 30 % (wt) of hydroxyapatite. In the composites the average size of 90 % of the HA particles was found to be below 6.5 mm. Cytotoxicity tests with the extract of the materials were performed in order to evaluate the presence and or release of toxic leachables and degradation products. Cell material interactions on the surface of the polymers were observed by scanning electron microscopy (SEM) and related to the materials formulations. The short-term effect of leachables from starch-based polymers was quantified by exposing L929 cell to the degradation products released by those materials after immersion in culture medium. 

Mendes and coworkers [275] described an extensive biocompatibility evaluation (in vitro and in vivo) of biodegradable starch-based materials aimed at orthopaedic applications as temporary bone replacement/fixation implants. For that purpose, they studied a polymer starch/ethylene vinyl alcohol blend (SEVA) and a composite of SEVA reinforced with HAp particles. As a result of their investigation it was found that SEVA and SEVA/HAp materials did not show relevant toxicity in both short- and long-term in vitro testing. Furthermore, when implanted in muscle or bone tissue, these materials induced a satisfactory tissue response. 

Commercial water-resistant starch based bioplastics are produced by using fine molecular blends of biodegradable synthetic polymers and starch. These materials are made with gelatinised starch (up to 60-85%) and hydrophilic synthetic polymers (e.g. ethylene vinyl alcohol copolymer) or hydrophobic synthetic polymers (e.g. polyeaprolactone or Ecoflex ) and compatibility agents (Fritz et al., 1994). The most important starch based material on the market is proposed by Novamont as Mater-Bi . 

The utilization of TPS for the production of biodegradable plastics has increased and has been the object of several studies in the last decade. However, TPS has two main drawbacks namely its water affinity and its poor mechanical properties. To overcome these problems, the addition of other materials to TPS is necessary. In order to increase its water resistance, TPS has been blended with synthetic polymers and modified by cross-linking agents such as Ca and Zr salts. Substances such as waxes and lignin have also been tested to decrease the water uptake of starch-based materials. TPS s mechanical properties have usually been improved by addition of synthetic polymers, such as ethylene-acryhc acid and ethylene-vinyl alcohol copolymers. Another approach requires the use of natural fibers and mineral fillers. The inclusion of reinforcing fillers such as fibers could, however, enhance the degradation of thermoplastic starch because of the increase in the melt viscosity [79-81]. 

---