Methods Currently Used in Testing Microbiological Degradation and Deterioration of a Wide Range of Polymeric Materials with Various Degree of Degradability: A Review

Biodegradation of polymeric materials affect a wide range of industries, information on degradability can provide fundamental information facilitating design and life-time analysis of materials. Among the methods currently used in testing, traditional gravimetric and respirometric techniques are tailored to readily degradable polymeric materials mostly and polymer blends with biodegradable components, but they are not applicable to the new generation of engineering polymers which are relatively resistant to biodegradation. However, electrochemical impedance spectroscopy (EIS) has been tested for monitoring biodeterioration of high strength materials and the technique has very high sensitivity. A wide range of materials including electronic insulation polyimides, fiber-reinforced polymeric composites (FRPCs) and corrosion protective polyurethane coatings have been successfully measured under inoculation of degradative microorganisms using EIS. In addition, the mechanism of degradation of high strength polymers is mainly due to the presence of plasticizers in the polymer matrices. The information on various methods discussed in this review is intended to illustrate a suite of methods for those who are interested in testing biodeterioration of polymeric materials under different environmental conditions and in selecting appropriate techniques for specific applications.     

Organoclays for Aquifer Bioremediation: Adsorption of Chlorobenzene on Organoclays and its Degradation by RHODOCOCCUS B528

The adsorption and degradation of chlorobenzene on partially modified organoclays and by the autochthonous microorganism Rhodococcus B528 were studied by means of the batch technique. Organoclays were prepared from Na-montmorillonite (MM) by using dodecyltrimethylammonium (C₁₂) and dioctadecyldimethylammonium (2C₁₈) bromides. The degree of modification was 35 (2C₁₈-35-MM) and 89% (C₁₂-89-MM) of the cation exchange capacity of MM. The adsorption experiments were carried out using headspace GC. The intercalation of chlorobenzene into the interlayers of organo-MM was detected by X-ray diffraction. The adsorption isotherms found were of the S1 type indicating a cooperative effect. Chlorobenzene showed a higher affinity for 2C₁₈-35-MM than C₁₂-89-MM, which could not only be explained by the organic carbon content. The comparison with 2,4-dichlorophenol adsorption has implied that for the studied systems the different adsorption mechanisms are primarily governed by the different molecular properties and not by the type of absorbent. The presence of 2C₁₈-35-MM caused no negative effect on the investigated microorganisms and complete biodegradation of chlorobenzene was achieved without desorption limitation for growth, demonstrating the applicability of partially modified organoclays for bioremediation.     

A New Test Method for Determining Biodegradation of Plastic Material Under Controlled Aerobic Conditions in a Soil-Simulation Solid Environment

A new test method is described for assessing biodegradation of plastic material under simulated soil conditions. An inert substrate can be activated with soil extract and nutrient and used in place of soil in biodegradation tests. The biodegradation level is evaluated by determining the carbon dioxide (CO₂) production released by the test reactors. Effects of substrate nature, solution pH, nutrient composition, soil extract concentration, and activation duration on CO₂ production were investigated, and the experimental conditions were optimized. Results obtained with cellulose showed a biodegradation rate of 80% within 28 days. Moreover, with this kind of substrate, reaction products and residues can be easily extracted and analysed.     

A Method for Measuring Degradation of Individual Components in Multicomponent Biodegradable Plastics by Fourier Transform Infrared Spectrometry

A new chemometric method based on Beer's law was derived that uses peak ratios from Fourier transform infrared spectra of neat polymers and their composite plastics to quantify degradation of the individual polymers after biodegradation. The method affords direct measurement of polymer concentrations and weight losses without prior calibration against known composites. Unlike traditional chemometric methods, this method does not require sampling of as many or more different composites as the number of polymers in the composite being analyzed. When the neat polymer spectra are known, only two measurements, one before and one after biodegradation, are needed. A potentially major advance is that the method allows automation of analytical infrared wavelength selection by computer from all possible wavelength combinations. In this paper, the theoretical basis and derivation of the mathematical model for multicomponent systems is presented. The validity of the model was proved initially by applying the method to simulated two-polymer and three-polymer composites and finally by comparing test results with known samples of biodegradable composites prepared in the laboratory. Potential future development of the method for more challenging multicomponent plastics is discussed.     

Kinetics of Aerobic Polymer Degradation in Soil by Means of the ASTM D 5988-96 Standard Method

The standard test method ASTM D 5988-96 for determining the degree and rate of aerobic biodegradation of plastic materials in contact with soil was applied to poly(3-hydroxybutyrate) and poly(-caprolactone). The method proved to be reliable and supplied reproducible measurements of CO₂ production, provided potassium (instead of barium) hydroxide was used as a trapping solution. The trends of CO₂ evolution, as a function of time, observed for the degradation of polymer powders in soil are similar to those predicted by simple first order kinetics in solution. The experimental data are described by a Michaelis–Menten type model, which accounts for the heterogeneity of the polymer-soil system. The kinetic equation deduced predicts the degradation rate to the proportional to the exposed polymer surface area.     

多壁碳纳米管修饰玻碳电极电化学氧化法测定痕量双酚A

分别采用循环伏安法和线性扫描伏安法研究了双酚A在多壁碳纳米管修饰玻碳电极上的电化学行为,并建立了一种灵敏简便的检测双酚A的电化学方法。实验结果表明:与裸玻碳电极相比,多壁碳纳米管修饰电极明显提高了双酚A的氧化电流;当外加电压为0～1.0 V、扫描速率为100 mV/s、缓冲溶液pH为5时,双酚A浓度分别在0.05～10.00μmol/L和20.00～100.00μmol/L的范围内与氧化峰电流呈良好的线性关系,检出限为0.013μmol/L。采用该修饰电极对实际试样进行加标回收实验,回收率为97%～104%。