Effect of Manufacturing Process and Xanthan Gum Addition on the Properties of Cassava Starch Films

The objective of this work was to manufacture biodegradable films by two different processes (casting and extrusion), from different combinations of cassava starch and xanthan gum. These films were produced by casting and by extrusion from six different starch-xanthan gum combinations (0, 2, 4, 6, 8 and 10% w/w), containing glycerol as plasticizer (20% w/w) and were also characterized according to their microstructure, optical, mechanical, and barrier properties. Scanning electron microscopy of the starch-xanthan gum extruded films showed reticulated surface and smooth interior, suggesting that xanthan was driven to the surface and gelatinized starch to the interior of the films during extrusion. Films manufactured by casting were entirely homogeneous. In general, casted films presented lower opacity and water vapor permeability and higher stress at break than films manufactured by extrusion. Xanthan gum addition affected mechanical properties of starch films, improving their stress and strain at break, especially for extruded samples, but these properties did not show stability at different RH conditions.     

The Effect of Acetylation on the Hydrolytic Degradation of PLA/Clay Nanocomposites

In this study, the hydrolytic degradation of Poly(lactic acid) (PLA) and acetylated PLA (PLA-Ac)–clay nanocomposites were investigated. The organo clay was obtained by ion exchange reaction using cetyl tri methyl ammonium bromide (CTAB). Nanocomposites containing 2, 5 and 8% mass ratio of organo clay (CTAB-O) were prepared. PLA and its organo clay nanocomposites were characterized by scanning electron microscope (SEM), thermo gravimetric analysis (TGA) and X-ray diffraction (XRD) to determine the morphology before and after hydrolytic degradation. Fourier transform infrared (FTIR) analyses of PLA and PLA-Ac were also obtained. The hydrolytic degradation of polymers and their composites were investigated in the phosphate buffered saline solution (PBS). The results showed that controlled hydrolytic degradation was observed in the samples with end group modification of PLA. While weight loss of PLA films was 28%, that of PLA-Ac films was 18% after 60 days degradation time. The weight loss was obtained as 29.5 and 25.5% for PLA-5 wt% organo clay (PLA/5CTAB-O) and PLA-Ac-5 wt% organo clay (PLA-Ac/5CTAB-O) nanocomposites films, respectively. It was also observed that thermal degradation of PLA-Ac was much more than that of PLA. Hydrolytic degradation increased depending on organo clay content. The end group modificated PLA results in controlled hydrolytic degradation. While hydrolytic degradation in polymer films occurred as surface erosion, bulk erosion was observed in composite films.     

Microbial Degradation of the Natural Rubber in Tire Tread Compound by a Strain of Nocardia

Tread compound of truck tires is based primarily on natural rubber or blends of natural rubber (NR) and synthetic polymers in combination with high grade carbon black. When the tread compound is attacked by a strain of Nocardia capable of degrading NR, part of the NR in the compound is mineralized, and part is disintegrated to very small black particles. The small black particles consist of the residual rubber and inorganic fillers. At higher NR content, large and deep cavities are formed on the surface of the pieces of the tread compound after microbial disintegration. At lower content of NR, large but very shallow cavities or very small pits can be seen on the tread surface. During microbial growth on the tread compound, isoprene oligomers with molecular weight of about two thousand are produced. Not only the isoprene oligomers, but also butadiene oligomers are produced during microbial disintegration of the tread compound of NR/synthetic rubber blend.     

Effect of Decalin Solvent on the Thermal Degradation of HDPE

The thermal cracking of HDPE in presence of different amounts of decalin was studied and compared with the reaction carried out in the absence of solvent. The decalin favours the mass and heat transfer during the reaction. In addition, it modifies the thermal degradation mechanism, which facilitates the formation of specific products. The use of decalin substantially increases the C₅–C₃₂ yield in comparison with the solventless reaction. In all cases, linear hydrocarbons such as n-paraffins, α-olefins and α,ω-dienes were detected. Increasing the decalin/plastic ratio led to enhanced α-olefin and n-paraffins yields, but the increase was more significant in the case of α-olefins, which are valuable compounds useful as raw chemicals. A reaction mechanism was proposed to explain the results obtained in presence of decalin. In these reactions, intramolecular radical transfer, secondary radical β-scission and hydrogen transfer from both decalin to intermediate radicals and from the polymer chain to regenerate the decalin play a significant role in determining the plastic conversion and the relative amounts of each product.     

The Effect of Interaction Between White-rot Fungi and Indigenous Microorganisms on Degradation of Polycyclic Aromatic Hydrocarbons in Soil

White-rot fungi applied for soil bioremediation have to compete with indigenous soil microorganisms. The effect of competition on both indigenous soil microflora and white-rot fungi was evaluated with regard to degradation of polycyclic aromatic hydrocarbons (PAH) with different persistence in soil. Sterile and non-sterile soil was artificially contaminated with ¹⁴C-labeled PAH consisting of three (anthracene), four (pyrene, benz[a]anthracene) and five fused aromatic rings (benzo[a]pyrene, dibenz[a,h]anthracene). The two fungi tested,Dichomitus squalens and Pleurotus ostreatus, produced similar amounts of ligninolytic enzymes in soil, but PAH mineralization by P. ostreatus was significantly higher. Compared to the indigenous soil microflora, P.ostreatus mineralized 5-ring PAH to a larger extent, while the indigenous microflora was superior in mineralizing 3-ring and 4-ring PAH. In coculture the special capabilities of both soil microflora and P. ostreatus were partly restricted due to antagonistic interactions, but essentially preserved. Thus, soil inoculation with P. ostreatus significantly increased the mineralization of high-molecular-weight PAH, and at the same time reduced the mineralization of anthracene and pyrene. Regarding the mineralization of low-molecular-weight PAH, the stimulation of indigenous soil microorganisms by straw amendment was more efficient than application of white-rot fungi.     

Environmental Degradation of Blends of Atactic Poly[(R,S)-3-hydroxybutyrate] with Natural PHBV in Baltic Sea Water and Compost with Activated Sludge

Degradation of atactic poly[(R,S)-3-hydroxybutyrate] (a-PHB) binary blends with natural poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV, 12 mol% of 3HV units), has been investigated and compared with plain PHBV in the compost containing activated sludge and under marine exposure conditions in the dynamic water of the Baltic Sea. Characteristic parameters of compost and the Baltic Sea water were monitored during the incubation period (6 weeks) and their influence on the degree of biodegradation is discussed. After specified degradation times of the experiments the weight loss of the samples, surface changes, changes in molecular weight and polydispersity as well as changes of the composition and thermo-mechanical properties of the blends have been evaluated. Macroscopic observations of the samples were accompanied by investigations using optical microscopy, size-exclusion chromatography (SEC), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC) and tensile testing. The degree of degradation of blends of a-PHB with PHBV depends on the blend composition and environmental conditions. In both environments studied the weight loss of plain PHBV was more significant than changes the molecular weight. In both environments only enzymatic degradation of the blends, which proceeds via surface erosion mechanisms, was observed during the incubation period.     

Effect of Hydrothermal Polylactic Acid Degradation on Polymer Molecular Weight and Surface Properties

In the present work, polylactic acid, PLA, samples were degraded by hydrothermal treatment, and then their molecular weights, crystallinity, surface charges and compositions, were determined, respectively, by using viscometry, ¹H NMR, Differential Scanning Calorimetry (DSC), microelectrophoresis and Infra Red spectroscopy methods. The viscometry and ¹H NMR data indicate that the molecular weight, of the polymer, decreases after the hydrothermal treatment. However, the crystalline fractions of the PLA samples, as obtained from the DSC and X-ray data, were not altered after the hydrothermal treatment. Furthermore, the zeta potential data, as determined by microelectrophoresis, show for both non-degraded and degraded PLA, an increase of the polymer surface charge density with the pH of the aqueous phase. However, at acidic pH values, the surface charge density for the degraded PLA was higher as compared to the non degraded one. These differences in surface charge densities of the PLA samples were confirmed by Infrared study, according to which the spectra of degraded polymer show the appearance of carboxyl groups occurring at 1,600 cm⁻¹ at the polymer surface.     

二氧化钛的改性及其对降解水中有机污染物的促进作用

综述了TiO2光催化剂的改性方法及其对光催化降解水中有机污染物的促进作用,介绍了复合物、煅烧温度、掺杂量、掺杂金属离子的种类和浓度对TiO2光催化性能的影响。     

Effect of Magnesium Oxide Loading on Adhesion Properties of ENR 25/NBR Blend Adhesives in the Presence of Petro Resin and Gum Rosin Tackifiers

The adhesion properties of magnesium oxide filled epoxidized natural rubber (ENR 25)/acrylonitrile-butadiene rubber (NBR) blend adhesives were studied using petro resin and gum rosin as tackifiers. Toluene was used as the solvent throughout the experiment. Five different loadings, i.e. 10, 20, 30, 40 and 50 phr magnesium oxide was used in the adhesive formulation. The SHEEN hand coater was used to coat the adhesive on polyethylene terephthalate at 30 and 120 µm coating thickness. The tack, peel strength and shear strength were determined by a Lloyd adhesion tester operating at 30 cm min^?1. Results shows that all the adhesion properties of the ENR 25/NBR adhesives show a maximum value at 10 phr filler loading. Loop tack and peel strength pass through a maximum, an observation which is associated to the optimum wettability of adhesive on the substrate. For the shear test, maximum shear strength occurs due to the optimum cohesive strength of the adhesive. Results also show that all petro resin based adhesives have higher adhesion properties than gum rosin based adhesive. In all cases, the adhesion properties of adhesives also increase with increasing coating thickness.     

Effect of Cell-to-matrix Ratio in Polyvinyl Alcohol Immobilized Pure and Mixed Cultures on Atrazine Degradation

Atrazine biodegradation by immobilized pure and mixed cultures was examined. A pure atrazine-degrading culture, Agrobacterium radiobacter J14a (J14a), and a mixed culture (MC), isolated from an atrazine-contaminated crop field, were immobilized using phosphorylated-polyvinyl alcohol (PPVA). An existing cell immobilization procedure was modified to enhance PPVA matrix stability. The results showed that the matrices remained mechanically and chemically stable after shaking with glass beads over 15 days under various salt solutions and pH values. The immobilization process had a slight effect on cell viability. With the aid of scanning electron microscopy, a suitable microstructure of PPVA matrices for cell entrapment was observed. There were two porous layers of spherical gel matrices, the outside having an encapsulation property and the inside containing numerous pores for bacteria to occupy. J14a and MC were immobilized at three cell-to-matrix ratios of 3.5, 6.7, and 20 mg dry cells/mL matrix. The atrazine biodegradation tests were conducted in an aerobic batch system, which was inoculated with cells at 2,000 mg/L. The tests were also conducted using free (non-immobilized) J14a and MC for comparative purpose. The cell-to-matrix ratio of 3.5 mg/mL provided the highest atrazine removal efficiency of 40–50% in 120 h for both J14a and MC. The free cell systems, for both cultures, presented much lower atrazine removal efficiencies compared to the immobilized cell systems at the same level of inoculation.     

Study on the Effect of Dicumyl Peroxide on Structure and Properties of Poly(Lactic Acid)/Natural Rubber Blend

In attempt to enhance the compatibility of NR in PLA matrix, and furthermore to enhance mechanical properties of PLA, PLA/NR blends with strong interaction were prepared in Haake internal mixer, using dicumyl peroxide (DCP) as cross-linker. The effects of dicumyl peroxide on morphology, thermal properties, mechanical properties and rheological properties of PLA and PLA/NR blends were studied. The results indicated that dicumyl peroxide could increase the compatibility of poly(lactic acid) and natural rubber. With small amount of dicumyl peroxide, the effect on NR toughening PLA was enhanced and the tensile toughness of PLA/NR blends was improved. When the DCP content was up to 0.2 wt%, the PLA/NR blend reached the maximum elongation at break (26.21 %) which was 2.5 times of that of neat PLA (the elongation at break of neat PLA was 10.7 %). Meanwhile, with introducing 2 wt% DCP into PLA/NR blend, the maximum Charpy impact strength (7.36 kJ/m²) could be achieved which was 1.8 times of that of neat PLA (4.18 kJ/m²). Moreover, adding adequate amount of DCP could improve the processing properties of blends: the viscosity of PLA/NR blend decreased significantly and the lowest viscosity of the blends could be achieved when the DCP content was 0.5 wt%.     

The Effect of Chain Extender on Poly(3-hydroxybutyrate-co-3-hydroxyvalerate): Thermal Degradation,Crystallization, and Rheological Behaviours

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a semi-polycrystalline biopolymer from the polyhydroxyalkanonate family has in recent years become a commercial bioplastic with mechanical properties comparable to isotactic polypropylene and enhanced O₂, CO₂ and H₂O barrier properties. However, its brittleness and sensitivity to thermal and hydrolysis degradations restrict its applications. To overcome the problems associated with degradation during processing blending of PHBV and an epoxy-functionalized chain extender (Joncryl^® ADR-4368 S) was conducted in a twin screw extruder. The effect of concentration of the chain extender on thermal, crystallization and rheological behaviours of PHBV was investigated. Thermal gravimetric analysis results indicated improvement in the resistance to thermal decomposition of PHBV by introducing the chain extender. This was accompanied with calculation of thermal degradation activation energy (E_a) using the Flyn–Walls–Ozawa method which confirmed increase of E_a with the increase in content of the chain extender. The rheological behaviour and crystallization of modified PHBV was characterized by rotational rheometry and differential scanning calorimetry techniques, respectively. The results show that addition of chain extender enhanced viscosity of PHBV and also reduce the rate of crystallization.     

论区域环境规划与区域开发环境影响评价在区域开发环境管理中的作用和地位

回顾了国内外区域开发环境管理的发展历程，简要论述了区域环境规划与区域开发环境影响评价在区域开发环境管理中的作用和地位以及两者的相互关系。     

Degradation of Cellulosic Materials Under the Alkaline Conditions of a Cementitious Repository for Low- and Intermediate-Level Radioactive Waste. II. Degradation Kinetics

The degradation of cellulosic materials, differing mainly in the degree of polymerization and the number of reducing end groups, was studied under the alkaline conditions similar to those existing in a cementitious repository for low- and intermediate-level radioactive waste (pH 13.3, T = 25°C). The kinetics of alkaline degradation (peeling-off reaction) were studied and the data analyzed by the model of Haas et al. [13]. The observed kinetic parameters for the propagation reaction and overall stopping reaction were compared with literature data. Although measured under different experimental conditions, literature data and data from this study show a consistent picture. Differences in the extent of degradation observed for the different cellulosic materials could be satisfactorily explained by differences in reducing end group content and, consequently, by differences in the degrees of polymerization. Besides the number of reducing end groups, the degree of amorphousness also plays an important role. The main degradation products formed under the experimental conditions used are - and -(gluco)isosaccharinic acid. This is in agreement with many other studies on alkaline degradation of cellulose. The two isomers are formed in roughly equal amounts.     

Effect of Metal Oxide Catalysts on Degradation of Waste Polystyrene in Hydrogen at Elevated Temperature and Pressure in Benzene Solution

Degradation of waste polystyrene is carried out in presence of hydrogen using several metal oxide catalysts at elevated temperature and pressure for recycling. Benzene is used as a solvent for degradation. Initial hydrogen pressure in the autoclave is kept at 7.0 kg/cm² (g) and polystyrene degradation is carried out at 240 °C. After degradation, degraded polystyrene residue is separated and analyzed by Fourier transform infra red (FTIR) spectroscopy whereas filtrate is analyzed by gas chromatography (GC) for finding the degradation mechanism of polystyrene. Degradation rate is enhanced in presence of hydrogen and time dependent weight average molecular weight of degraded polystyrene is determined using viscosity method. Degradation rate constants for the different catalysts are calculated based on the proposed degradation mechanism. Alkali metal oxide catalyst shows higher reactivity towards polystyrene degradation as compare to the transition metal oxide catalyst i.e., degradation rate constant decreases with the increase in electro negativity of metal element of the catalyst. Though manganese (IV) oxide is a transition metal catalyst, but shows higher reactivity due to its reduction towards stable manganese (II) oxide under degradation environment. Finally, degradation rate constant of polystyrene is correlated with the catalyst activity i.e., electro negativity of metal element in the catalyst.     

Effect of Nucleating Agents on Physical Properties of Poly(lactic acid) and Its Blend with Natural Rubber

Poly(lactic acid) (PLA) presents high strength and modulus, but very low toughness as well as slow crystallization. Natural rubber (NR) was blended to enhance the toughness and nucleating agent was added to improve the crystallization. Cyclodextrin (CD), considered as a green compound, as well as calcium carbonate (CaCO₃) and talc were used as nucleating agents. Effects of these nucleating agents on crystallization, mechanical properties and morphology of neat PLA and PLA/NR blend were investigated. It was found that the addition of talc and CD decreased cold crystallization temperature (T_cc) of the PLA. Same result was obtained in PLA/NR blend containing talc. All nucleating agents increased the degree of crystallinity (Χ_C) of PLA, whereas only talc and CaCO₃ increased Χ_C of PLA in PLA/NR blends. The enhanced toughness of PLA by the addition of nucleating agent was attributed to its increased crystallinity, as well as decreased spherulite size. For PLA/NR blends, the increase in toughness was mainly contributed by the presence of the rubber.