An Assessment of Biodegradability and Phytotoxicity of Natural Rubber in a Simulated Soil Condition via CO2 Evolution Measurement.

In this study, the biodegradation of various natural rubber (NR) samples, i.e., neat NR and NR filled with two different curative contents was investigated under a long-term simulated soil condition at a temperature of 25 ± 2 °C in accordance with ISO 17556. Natural clay loam soil, with a pH of 7.2 and a water holding capacity of 57.6%, was employed. Under controlled test condition both unvulcanized and vulcanized NR samples having low curative content, respectively designated as UNRL and VNRL, exhibited similar biodegradation behaviors to the neat NR. They showed fast biodegradation at the early stage, and their biodegradation rate did not significantly change throughout the test period (365 days). However, for the NR samples having high curative content, respectively called UNRH and VNRH for the unvulcanized and vulcanized samples, a biodegradation delay was observed within the first 130 days. Surprisingly, the UNRH showed a relatively high biodegradation rate after the induction period. At the end of the test, most of the rubber samples (the neat NR, UNRL, VNRL, and UNRH) showed a comparable degree of biodegradation, with a value ranging from 54-59%. The VNRH, on the other hand, showed the lowest degree of biodegradation (ca. 28%). The results indicate that the number of curatives does not significantly affect the biodegradability of unvulcanized NR in the long term, despite the fact that a high curative content might retard microorganism activity at the beginning of the biodegradation process. Apparently, crosslink density is one of the key factors governing the biodegradability of NR. The phytotoxicity of the soils after the biodegradation test was also assessed and represented in terms of seedling emergence, survival rate, and plant biomass for Sorghum bicolor. The values of seedling emergence (≥80%), survival rate (100%), and plant biomass of all soil samples were not statistically different from those of the blank soil, indicating the low phytotoxicity of the tested soils subjected to the biodegradation of the rubber samples. Taken as a whole, it can be concluded that the CO2 measurement technique is one of the most effective methods to assess the biodegradability of rubbers. The knowledge obtained from this study can also be applied to formulate more environmentally friendly rubber products.

Fabrication and physical properties of a novel macroporous poly(vinyl alcohol)/cellulose fibre product.

The objective of this work was to prepare functionalized cellulose fiber from sugar cane leaf (SCF) used to produce novel biomaterial. The SCF was treated with chloroacetic acid and sodium hydroxide (NaOH) to produce a modified cellulose fibre (MSCF). At higher MSCF loading, a greater porous density was observed under SEM. The addition of MSCF improved, the water resistance of the cured PVA/MSCF in both acid and base media through chemical reactions. The moisture absorption and moisture content of the cured PVA/MSCF film increased as the loading increased MSCF. Tg of the cured PVA/MSCF showed a clear decrease that was attributed to the greater molecular weight and softness of the molecular chains. The cured PVA/MSCF showed good MB absorption from wastewater. The improvement in biodegradability of the cured PVA/MSCF film may make it a candidate material for use in environmentally-sensitive applications.

Biodegradable kinetics of plastics under controlled composting conditions.

This study models and evaluates the kinetics of C-CO(2) evolution during biodegradation of plastic materials including Polyethylene (PE), PE/starch blend (PE/starch), microcrystalline cellulose (MCE), and Polylactic acid (PLA). The aerobic biodegradation under controlled composting conditions was monitorated according to ISO 14855-1, 2004. The kinetics model was based on first order reaction in series with a flat lag phase. A non-linear regression technique was used to analyze the experimental data. SEM studies of the morphology of the samples before and after biodegradation testing were used to confirm the biodegradability of plastics and the accuracy of the model. The work showed that MCE and PLA produced the high amounts of C-CO(2) evolution, which gave readily hydrolysable carbon values of 55.49% and 40.17%, respectively with readily hydrolysis rates of 0.338 day(-1) and 0.025 day(-1), respectively. Whereas, a lower amount of C-CO(2) evolution was found in PE/starch, which had a high concentration of moderately hydrolysable carbon of 97.74% and a moderate hydrolysis rate of 0.00098 day(-1). The mineralization rate of PLA was 0.500 day(-1) as a lag phase was observed at the beginning of the biodegradability test. No lag phase was observed in the biodegradability testing of the PE/starch and MCE. The mineralization rates of the PE/starch and MCE were found to be 1.000 day(-1), and 1.234 day(-1), respectively. No C-CO(2) evolution was observed during biodegradability testing of PE, which was used for reference as a non-biodegradable plastics sample.