Starch thermo-oxidation

The initiation of thermo-oxidation of polyethylene films by transition metal catalysts during composting proceeded slowly compared to oxidation at the same temperature in an oven (60-70 °C) [56]. The starch-filled polyethylene bags exposed on the surface of the compost broke down into small pieces while the buried bags remained intact after 49 days of exposure [55,... 

The optimum temperature for the vacuum pyrolysis of starch and cellulose lies around 350°. At lower temperatures (—200°), dehydration, particularly in the presence of inorganic salts, and thermo-oxidation accompanied by partial depolymerization and progressive carbonization predominate at temperatures above 500°, ready carbonization and decomposition of the primary pyrolysis-products occur. Low pressures favor the formation of levoglucosan, which should be rapidly removed from the pyrolysis oven by a flow of an inert gas, preferably, superheated steam.171,172,178,179,181,182,209... 

Generally [17] 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 that catalyse the photo and thermo-oxidative process [18-21]. 

Erlandsson B, Karlsson S, Albertsson A.-C (1997) The mode of action of com starch and pro-oxidant system in LDPE influence of thermo-oxidation and UV-irradiation on the molecular weight changes. Polymer degradation and stability. 55 237-245. 

Crystalline starch beads can be used as a natural filler in traditional plastics [3]. They have been particularly used in polyolefins. When blended with starch beads, polyethylene films biodeteriorate upon exposure to a soil environment. The microbial consumption of the starch component leads to increased porosity, void formation, and loss of integrity of the plastic matrix. Generally, starch is added at fairly low concentrations (6-15 wt%). The total disintegration of these materials is obtained using transition metal compounds, soluble in the thermoplastic matrix, used as pro-oxidant additives to catalyze the photo and thermo-oxidative processes [4]. These products belong to the first generation of degradable polymers that biodeteriorate more than mineralize to CO2 and H2O in a time... 

Thermo-oxidation increases the degradation rates considerably. During this type of degradation both molecular reduction and molecular enlargement reactions occur [9]. In starch-filled LDPE containing pro-oxidant in addition to starch it was shown that oxidation at 100°C initiates carbonyl formation after 5 days compared to pure LDPE which is unaffected under the same conditions at [10]. 

Addition of corn starch to LDPE has a stabilizing effect on the thermo-oxidation mode while the same additive destabilizes the LDPE to UV irradiation. This property would diminish the risk of degradation during the processing of such materials. 

To increase the starch load up to 40-60% in PO a gelatinized starch is used in the films of poly(ethylene-co-acrylic acid) (EAA) or a mixture of EAA/LDPE or LDPE/EMA (ethylene-maleic anhydride). The difficulty with this system is that the high level of filler seriously impairs the mechanical properties, especially in thin films, and the starch is subjected to moisture-absorption problems. LDPE Mn stea-rate/starch showed a decrease of MW during thermo-oxidation and an increase of MW during UV irradiation. In the mixtures, it has been estabhshed that ethylene-acrylic acid copolymer accelerates LDPE oxidative degradation while plasticized starch inhibits it [62]. 

Figure 2. Chemiluminescence, measured in a nitrogen atmosphere of different LDPE samples. Thermo-oxidized (lOOrC) A = LDPE and LDPE+7.7% starch B = LDPE + 7.7% MB C = LDPE + 15% MB and D = U)PE =...

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