Plasticization of starch

Conventionally, plasticization of starches, modified starches and amylose have often been attempted often without satisfactory results. The development of these applications was accomplished by the discovery of a process to decompose carbohydrates into glucose units and rearrange these into pullulan. Pullulan is advantageous in view of environmental pollution prevention, because the process is biochemically based and neither requires an enormous energy consumption nor releases or generates excess heat or harmful gas. 

It is well know that in the plasticization of starch, a phase transition occurs and the phase transition degree determines the process ability and the final product properties. Xie et al. (2014) claim that during the processing of starch, it is also important to know and control the rheological behavior of plasticized starch to prevent flow engineering problems and maintain the final product quality (Xie et al. 2012). Then, in processed plasticized starch-based materials, the phase transition and rheology are the two most important aspects to take into account, and the understanding of the materials melt flow results necessary. 

Dufresne et al. (2000) reported a 350 % increase in tensile modulus of MFC/ starch nanocomposites at 50 wt% cellulose content compared to neat starch. However, at high humidity levels (75 % RH), the reinforcing effect was clearly diminished. This was attributed to the hydrophilic nature of both the starch and the cellulose, which resulted in the plasticization of starch and weakening of cellulose/ starch interfacial adhesion. On the other hand, the addition of cellulose to starch resulted in a decrease of both water uptake at equilibrium and the water diffusion coefficient. 

Current investigations are aimed at providing polymers derived from renewable resources but with electroactive properties. For example, an ionic liquid (l-butyl-3-methyl imidazolium chloride BMIM-Cl) was used as a plasticizer in starch, zein and their blends, and compared to glycerol, as a classical plasticizer of starch [96]. 

Starch is being viewed as a sustainable polymer which can be modified to afford new types of materials. In this regard plasticization of starch to yield stable composites is of interest. A hexa substituted derivative (78) was prepared and utilized as a plasticizer for starch. It has been reported that at a composition of 20 wt% of the cyclophosphazene input plasticizer, the composite showed a high tensile modulus of 1.12 Gpa and a yield strength of 20.9 Mpa while still showing a large strain of 8.8%. Importantly no retro degradation of the composite was observed even after 2 months." ... 

Starch is made thermoplastic at elevated temperatures ia the presence of water as a plasticizer, aHowiag melt processiag alone or ia blends with other thermoplastics (192—194). Good solvents such as water lower the melt-transition temperature of amylose, the crystalline component of starch, so that processiag can be done well below the decomposition—degradation temperature. 

Electric road vehicles have been reduced to insignificance, as mentioned already by, vehicles with combustion engines. Another electric vehicle — the electrically driven submarine — presented a continuous challenge to lead-acid battery separator development since the 1930s and 1940s. The wood veneers originally used in electric vehicles proved too difficult to handle, especially if tall cells had to be manufactured. Therefore much intense effort took place to develop the first plastic separators. In this respect the microporous hard rubber separator, still available today in a more advanced version, and a micro-porous PVC separator (Porvic I) merit special mention 28]. For the latter a molten blend of PVC, plasticizer and starch was rolled into a flat product. In a lengthy pro-... 

In the homogenous mixture of Starch and Polyvinyl alcohol (PVA), 30 % of plasticizer was mixed to make Pure blend. Then 10 % cellulose was mixed into above mixture followed by removal of extra water gave Cellulose-Reinforced starch-PVA blends. The different proportions of Fly ash were mixed into mixture of Cellulose-Reinforced starch-PVA blends to get various fly ash inserted Cellulose-Reinforced starch-PVA blends. Solubility, swelling behaviour and water absorption studies of Fly ash blends were measured at different time intervals at relative humidity of 50-55%. The insertion of Cellulose into starch-PVA blend decreases the solubility of blends due to the hydrophobicity of cellulose, but the solubility further increases by insertion of Fly ash into starch-PVA matrix that indicating the mechanical stability enhancement of blends. The water absorption behaviour of fly ash blends increases rapidly upto 150 min and then no change. The optimum concentration of Fly ash into Cellulose-Reinforced starch-PVA blend was 4%. 

Figure 1. Possible routes for biological and chemical degradation of starch-plastic composites. Note that direct biological degradation of petrochemical-based polymers does not occur. Rather, these polymers must first undergo chemical degradation to form as yet uncharacterized, lower molecular weight intermediates.

Figure 4> Effects of three different cultures of starch-degrading bacteria on the weight of starch/P / AA plastic films incubated in liquid culture. The bacterial cultures used (identified as LD54 (o), LD58 ( ) and LD76 (A)) are composed of proprietary starch-degrading bacteria isolated by the USDA.

Figure S. Effects of three different cultures of starch-degrading bacteria on the tensile strength of starch/PE/EAA plastic films. See legend to Figure 4 for details.

Figure 7. Effects of amylolytic bacteria of the FTIR spectrum of starch/P / AA plastic films (a) film incubated for 24 hours in sterile medium (b) film incubated for 28 days in sterile medium and (c) film incubated for 28 days in medium inoculated with LD76.

Figure 8. Rate of starch disappearance from starch/P / AA plastic films incubated with a culture of starch-degrading bacteria (LD76). The proportion of starch remaining in the film was estimated from FTIR spectra as the integrated absorbance over the range 960-1190 cm". ...

At this point little is known about the interrelationships between composition, structure, starch-degradation and physical disintegration properties of starch-plastic composites. Continued work towards development of a laboratory assay for biodegradability will eventually result in the establishment of a sufficient database to elucidate these relationships, allowing development of a host of starch-containing plastic products for both existing and new markets. 

According to filler theory, connectivity can be achieved at lower values when the filler form is plates rather than spheres. Depending on the proportions of the plates and whether or not an inactive phase is included in the blend, connectivity can be achieved at 8 to 16% (v/v) filler (4). The starch-plastic blends developed by Otey (2) have a laminate structure when the starch content is under 30% by volume (Figure 1) and the threshold for microbial attack on these materials is under 13% starch by volume (Figure 2). This low threshold value can be explained by considering the LDPE as a non-conductive (enzyme-impermeable) phase combined with a conductive phase of starch-EAA complex. 

Figure 3. Postulated mechanism for microbial decay of starch-plastic blends.

For the reasons stated above, deep intrusion of degrading microbes into polysaccharide-plastic films is demonstrably and theoretically improbable. Since starch removal does occur when the films are buried in soil, the primary mechanism must be microbial production of amylase in or near a pore, diffusion of the enzyme into pores and diffusion of soluble digestion products back to the surface where they are metabolized (Figure 3). This mechanism would be the only choice when the pore diameter is too small to admit a microbial cell (i.e., at diameters < 0.5 /im). An alternative mechanism could be diffusion of a water-soluble polysaccharide to the film surface, at which point degradation would occur. None of the materials used in these investigations showed loss of starch even when soaked in water for extended periods with microbial inhibitors present. Therefore, diffusion of amylase to the substrate rather than diffusion of the substrate to the film surface is the more likely mechanism. 

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