Blending with starch

The second section deals with the degradability of commodity plastics and specialty potymers. Emphasis is on the biodegradation of polyethylene, its blends with starch, and constraints in the decay of such composites. Additionally, the biodegradability of different functional groups (polyethers, carbotylic adds, esters, and dioxanones) is mcamined with respect to composition and miaostructure. 

A series of 10 polycyclic compounds and blends with starch, Bakelite, and hydrogenated creosote were employed as model substances to examine the effect of carbon, hydrogen, and oxygen on sulfur distribution during pyrolysis at a temperature of about 625°C. 

Copolymers of polyethylene terephthalate (PET) with nonaromatic acids, poly(ethylene ethers) or hydroxy acids have been blended with starch to produce compostable products such as fibers and films.60 Starch contents up to 80% by weight are claimed. 

One of the first synthetic polymers to be blended with starch was poly(vinyl alcohol) (PVA). Otey et al.129,130 prepared cast films of starch and PVA from aqueous solutions containing a plasticizer (glycerol). Films were cast onto glass plates and air-dried at 130°C. Small amounts of crosslinking agent, such as formaldehyde,... 

Surimi is fish paste from deboned fish used to make simulated crab legs and other seafood. For preservation the paste is blended with cryoprotectants, such as sucrose, sorbitol and phosphates, and frozen. To make the final product, the frozen paste is thawed, blended with starch and extruded as a film onto a belt. The belt takes the film into an oven that heat-denatures the fish protein and cooks the starch. The film is then rolled to form striations, shaped, colored and cut. Depending on the required distribution, the product is frozen or refrigerated. Potato and tapioca starch were used in surimi products 400 years ago, since they provided a cohesive, elastic matrix consistent with seafood. Frozen distribution has made the use of highly-stabilized, moderately crosslinked tapioca starch popular, alone or with native tapioca starch. Modified waxy maize products are used, as is unmodified com starch, for increased cuttability. Kim188 reported that the gel strengthening ability of starch correlates with starch paste viscosity. 

A range of preblended sizes to satisfy any staple yarn requirement at a reasonable cost. The products are free flowing powders based on acrylic and other vinyl polymers blended with starch. Wax is included in appropriate products. 

Starch dialdehyde condenses readily with amino amides2624 and diamines,2625 and forms oximes with hydroxylamine.2626 The reaction of starch dialdehyde with isoniazid, 4 -formacelanilide thiosemicarbazone, 4 - amin o b e n z a I de h y de thiosemicarbazone or thiosemicarbazone, produced the corresponding condensation products.613-615 617 2627-2629 Hydrazones were readily formed when hydrazine and its derivatives were blended with starch dialdehyde and acidified with acetic acid2543,2630 or simply on heating the reaction mixture.2631 Condensation of starch... 

Poly-8-caprolactone (PLC) is a synthetic, biodegradable (both linear and cross-finked) polyester with MW > 20 kg/mol. It may be processed as a thermoplastic. Owing to miscibility with PVC it is used as plasticizer and frequently blended with starch to use for films, sheets and injection molded parts, viz. Mater-Bi (see Part 16.8.1). PCL is manufacmred by Union Carbide, Daicel and Interox. Its mechanical properties are similar to these of PE [Bastioli, 1997]. 

Innocentini-Mei, L. H., Bartoli, J. R Baltieri, R. C., Mechanical and thermal properties of poly(3-hydroxybutyrate) blends with starch and starch derivatives. Macromolecular Symnosia. 1, 77-88 (2003), DOl 10.1002/masy.200350708. 

When blended with starch beads, PE films [16] deteriorate on exposure to a soil environment. The microbial consumption of the starch component, in fact, leads to increased porosity, void formation, and the loss of integrity of the plastic matrix. 

PLA PLA-based block copolymers include diblock, triblock, and multiblock copolymers Jeon et al. (20(B), Chen et al. (2003), Pospiech et al. (2005) Blend with starch, other polyesters, and low molecular weight plasticizers such as glyc ol, sorbitol, and triethyl citrate Cargill (2007)... 

Blends of starch with polar polymers containing hydroxyl groups, such as poly(vinyl alcohol), copolymers of ethylene and partially hydrolyzed vinyl acetate have been prepared since the 1970s, as described by Otey et al. [61, 68-72]. Since starch and other natural polymers are hydrophilic, water has been commonly used as a plasticizer for these materials. The possibility of using water as plasticizer makes it possible to add the polymer to be blended as an aqueous emulsion, as for example, in the case of natural rubber latex [112], poly(vinyl acetate) and other synthetic polymer lateces [71,113,114]. Blends of starch and biodegradable polymers and polymers from renewable resources have been reviewed recently due to their growing importance [82, 110, 111, 115, 116]. Table 15.3 gives some polymers commonly used in blends with starch. 

Starch blends can be divided into two main categories according to (1) the source and biodegradation properties of the polymer to be blended with starch and (2) the process used for its preparation. As for the first category, the sources can be obtained directly from renewable resources (biodegradable biopolymers), can be synthetic polymers from either oil or renewable resources, and in this latter case they can be biodegradable or not depending on their structure. 

Linear low-density polyethylene, LLDPE, was blended with starch and at least one ionic compound (in such amount that the concentration of anions and cations was between 0.002 and 5 mol kg ) to produce high-frequency sealable articles. The starch could also contain <50 wt% of a plasticizer. The alloys could be processed by calendering. 

In order to improve the mechanical properties of the materials, polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), and other polyesters can be blended with starch. Starch and PBS or PBSA blends produce biodegradable plastic sheets with diversified applications like trays and other film products. Though with increase in starch content, there is decrease in tensile strength but biodegradability of the product keeps on increasing. Plasticizers are added to avoid the brittleness of the products and to increase the flexibility and end uses. 

The same authors fabricated PLA/starch blends with various concentrations of two natural antioxidants, a-TOC and resveratrol, by melt blending and compression moulding processes. The sheets showed a yellowish colour and a significant reduction in the glass transition and melting temperatures. The addition of these agents enhanced mechanical properties, an effect which is attributed to a compatibilization effect between PLA and starch chains. A detailed study of the release process showed that blending with starch accelerated the release of resveratrol and a-TOC from PLA into ethanol. 

Starch can be nsed as a natural filler in traditional plastics (11,23-33) and par-ticnlarly in polyolefins. When blended with starch beads, polyethylene films (34) biodeteriorate on exposure to a soil environment. The microbial consumption of the starch component, in fact, leads to increased porosity, void formation, and the loss of integrity of the plastic matrix. Generally (32,35-38), starch is added at fairly low concentrations (6-15%) the overall disintegration of these materials is achieved by the use of transition-metal compounds, soluble in the thermoplastic matrix, as pro-oxidant additives which catalyze the photo- and thermooxidative process (39-44). 

HDPE, NR and thermoplastic tapioca starch (TPS). Several previous studies have reported that blends with starch exhibit a marked decrease in tensile properties because the incorporation of starch interferes in the adhesion between the component phases.Therefore, based on this research work, the mechanical properties were improved by NR vulcanization, which compensated for the deterioration in properties due to TPS loading. 

It is important to note that the distribution of MDI had a clear effect on the mechanical properties of blends, with the highest values recorded for blends where MDI was distributed in the PLA phase prior to blending with starch. This phenomenon can be explained by the tendency of the highly reactive isocyanate groups in MDI to react with the water absorbed in starch, as shown in Figure 15.3. 

The Tg of PLA was relatively unaffected by blending with starch, either with or without MDI, due to continued phase separation. MDI appeared to enhance the cold crystallization of PLA, and for the blends where MDI was distributed in the... 

However, beeause of its signifieant brittleness and high cost, PHB is virtually always employed in the form of blends with starch, cellulose, PE... 

The interfacial interaction between poly(lactic acid) (PLA) and starch was improved and mechanical properties of PLA blends with starch were enhanced by an addition of methylene diisocyanate (MDI) [111-112]. 

Dos Santos Rosa D, Rodrigues T.C., das Gramas Eassina Guedes C., Cahl M.R. Effect of thermal aging on the biodegradation of PCL, PHB-Y and their blends with starch in soil compost, J. Appl. Polym. Sci. 89 (2003) 3539. 

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