Assessing Aerobic Biodegradability of Plastics in Aqueous Environment by GC-Analyzing Composition of Equilibrium Gaseous Phase

Testing biodegradability of plastics under varied conditions of the environment as well as under laboratory conditions in accordance with valid international standards is very laborious, lengthy and often also economically demanding. For this reason, applicability was verified of gas chromatography to analyze gaseous phase when investigating the biodegradation course of plastics in an aqueous environment as an alternative to customary employed methods. A mathematical model of acid–basic CO₂ equilibrium in a gas–liquid system was worked out, enabling to determine quantity of produced CO₂ through chromatographic analysis of gaseous phase, in dependence on ratio of liquid and gas phase volumes (V _l/V _g) and on actual pH of liquid phase. Experimental conditions for organizing the tests were optimized. A ratio that proved suitable was V _l/V _g ≅ 0.1 at pH ≈ 7.1 of liquid phase. Under these test conditions, biodegradability of model samples, PHB, Gellan gum and Xanthan gum, was explored; course of biodegradation was studied through produced CO₂ (values ) determined by analyzing gaseous phase through gas chromatography on the one hand, and through customary “titration” procedure on the other. With water-soluble polymers, the decrement in dissolved organic carbon (values D _DOC) was also studied. Difference between values does not exceed 5%. The procedures in question are alternative “substituting” procedures for observing course of aerobic biodegradation of substances in an aqueous environment.     

Modelling Easily Biodegradability of Materials in Liquid Medium-Relationship Between Structure and Biodegradability

In the present project, twenty materials (e.g., polyhydroxybutyrate-hydroxyvalerate, polycaprolactone, cellulose acetate, polyacticacid, polyethylene), representing varied biodegradability levels were studied. An aerobic respirometric test, based on the CEN Draft, was setup. The biodegradability of each plastic film was evaluated by measuring the percentage of carbon converted into CO₂ during 35 days. The values of the CO₂ production were plotted versus days as a cumulative function. In order to reduce its number of points, the cumulative curve was modeled using a sigmoïd function (Hill sigmoïd). This model was compared to one found in the literature. A _i ² test showed that the biodegradation curve was more accurately fitted with the model than the previous one. Three kinetic parameters were determined by this Hill model: one represents the maximal percentage of carbon converted into CO₂, the second the half-life time in days of the degrading part of the material and the third one the curve radius.In addition, the following analyses were carried out on each sample: elemental analysis, thickness, hydrophobicity and surface free energy measurements. In order to compress the information and to keep only relevant pieces, these parameters were submitted to a Principal Component Analysis. PCA found linear combinations of variables that describe major trends in the data. The two principal components which separate groups of materials were closely related to a chemical and a physical axis respectively. Materials showing a high biodegradability were related to high oxygen (and nitrogen) contents and low hydrophobicity: Material thickness did not influence the likeliness to biodegradability described by the maximum biodegradation rate. Finally, this study established the correlation between the biodegradation and the structure of biopolymers.     

Miscibility and Biodegradability of Poly(Butylene Succinate)/Poly(Butylene Terephthalate) Blends

As one of the biodegradable polymers, the blend of poly(butylene succinate) and poly(butylene terephthalate) is dealt with in this study. In our previous work, it was demonstrated that PBS and PBT are immiscible not only from the changes of T _g but also from logG–log G plots. It is expected that the biodegradability of the blends could be improved by enhancing the miscibility. We tried to induce the transesterification reaction between two polyesters with various time intervals to enhance the miscibility of the blends. The extent of transesterification reaction was examined by ¹H-NMR. We utilized a dynamic mechanical thermal analyzer and a rotational rheometer to investigate the changes in miscibility. We also verified the biodegradability of PBS/PBT blends after the transesterification reaction by the composting method.     

Thermal Properties and Biodegradability Studies of Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

For investigating the relationship between thermal properties and biodegradability of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), several films of PHBV containing different polyhydroxyvalerate (HV) fractions were subjected to degradation in different conditions for up to 49 days. Differential scanning calorimetry (DSC), thermogravimetry (TG), specimen weight loss and scanning electron microscopy (SEM) were performed to characterize the thermal properties and enzymatic biodegradability of PHBV. The experimental results suggest that the degradation rates of PHBV films increase with decreasing crystallinity; the degradability of PHBV occurring from the surface is very significant under enzymatic hydrolysis; the crystallinity of PHBV decreased with the increase of HV fraction in PHBV; and no decrease in molecular weight was observed in the partially-degraded polymer.     

Effect of Crystalline and Amorphous Structures on Biodegradability of Poly(Tetramethylene Succinate)

The effect of orientation in the amorphous and crystalline regions on the biodegradability of PTMS [poly(tetramethylene succinate)] was studied using the amorphous orientation function, birefringence, and crystallinity. The crystalline and amorphous intrinsic lateral sonic moduli, E _t,c ⁰ and E _t,am ⁰ , were 2.61 × 10³ and 0.41 × 10³ MPa, respectively. Using the data on birefringence, crystalline and amorphous orientation function (f and f _am), crystallinity, and sonic modulus of the oriented PTMS fibers, the intrinsic birefringence of the crystalline ( _c ⁰ ) and amorphous ( _am ⁰ ) regions were evaluated to be 0.0561 and 0.0634, respectively. The biodegradabilities of oriented PTMS films were reduced as the elongation increased, i.e., the amorphous orientation increased. At low elongation (100 and 150%), however, biodegradabilities remained unchanged when the degradation test was performed in activated sludge, which was attributed to the amorphous orientation occurring even at 100% elongation, though the amorphous orientation direction was perpendicular to the fiber axis.     

Radiation Crosslinking of Poly(Butylene Succinate) in the Presence of Inorganic Material and Its Biodegradability

Three kinds of poly(butylene succinate)s (PBS) with different molecular weight were irradiated with electron beams in the presence of inorganic material. Fourteen kinds of inorganic materials were used in this work. The presence of inorganic material inside cross-linked PBS samples enhances the yield of gel formation. The heat stabilities of PBS samples were checked; it was found that silicon dioxide and carbon black significantly improve these properties. Enzymatic and soil burial tests were performed; the presence of these inorganic materials in cross-linked PBS accelerates the rate of biodegradation.     

Life Cycle Assessment of Poly(Lactic Acid) (PLA): Comparison Between Chemical Recycling,Mechanical Recycling and Composting

This paper presents a life cycle assessment (LCA) comparing three forms of poly(lactic acid) (PLA) disposal: mechanical recycling, chemical recycling and composting. The LCA data was taken from lab scale experiments for composting and hydrolysis steps. Polymerization data in chemical recycling was obtained from computer simulation. Mechanical recycling data from lab scale were combined with the data from a plastics commercial mechanical recycling plant. The analysis considered two different product systems based on the input of the recycled PLA in the product system. Considering the categories: climate change, human toxicity and fossil depletion, the LCA showed that mechanical recycling presented the lowest environmental impact, followed by chemical recycling and composting. Among the forms of recycling, the most important input was the electricity consumption.     

Processability and Biodegradability Evaluation of Composites from Poly(butylene succinate) (PBS) Bioplastic and Biofuel Co-products from Ontario

This study investigates the processability and biodegradability of composite bioplastic materials. Biocomposites were processed using twin-screw compounding of the bioplastic poly(butylene succinate) (PBS) with bio-based fillers derived from co-products of biofuel production. An extensive biodegradability evaluation was conducted on each biocomposite material, as well as the base materials, using respirometric testing to analyze the conversion of organic carbon into carbon dioxide. This evaluation revealed that the presence of meal-based fillers in the biocomposites increased the rate of biodegradation of the matrix polymer, degrading at a faster pace than both the pure PBS polymer and the switchgrass (SG) composite. This degradation was further confirmed using FT-IR and thermal analysis of the material structure before and after biodegradation. The increased biodegradation rate is attributed to the high concentration of proteins in the meal-based composites, which enhanced the hydrolytic biodegradation of the material and facilitated micro-organism growth. The SG-based composite degraded slower than the pure polymer due to its lignin content, which degrades via a different mechanism than the polymer, and slowed the biodegradation process.     

Biodegradability and Mechanical Properties of Poly(vinyl alcohol)-Based Blend Plastics Prepared Through Extrusion Method

Plastic blend materials consisting of poly(vinyl alcohol), glycerol and xanthan or gellan were prepared through laboratory extrusion. Their base mechanical properties were compared with the properties of poly(vinyl alcohol) foil and their biodegradability in soil, compost and both activated and anaerobic sludge were assessed. In samples with lower polysaccharide content (10–21 %w/w) the tensile strength of 15–20 MPa was found; the elongation at break of all blends was relatively close to the parameter of poly(vinyl alcohol) foil. The biodegradability levels of the blends tested corresponded to the content of natural components, and the mineralization of the samples with the highest carbohydrate proportion (42 %) reached 50–78 %, depending on the type of the environment. Complete biodegradation of all samples occurred in activated sludge.     

Biodegradation Behaviors of Poly(p-dioxanone) in Different Environment Media

This work was aimed at researching the aerobic biodegradation of poly(p-dioxanone) (PPDO), a novel kind of degradable polymer material, by simulating real-life conditions in a laboratory-scale test, specified by the standard methods based on two biodegradation environments, composting and aqueous media. To measure and describe the biodegradability of PPDO, not only had carbon dioxide produced by respiratory metabolism of microorganism been measured, which determines the ultimate aerobic biodegradability of chemical compounds, but also the detailed results of biodegradation were further characterized by monitoring physical, chemical and thermal properties changes of test materials at different incubation times in the two media, confirmed by using the appropriate analytical techniques. Scanning electron microscopy was used to observe the surface morphology, and the thermal performance of PPDO was characterized by differential scanning calorimetry. The changes of molecular weight were detected by intrinsic viscosity ([η]) and gel permeation chromatography, and the variations of the molecular structure were monitored by the nuclear magnetic resonance and FT-IR. The results show that PPDO has outstanding character of biodegradation and may be more adapted for biodegrading in liquid medium than in composting.     

Thermal and Rheological Properties of Commercial-Grade Poly(Lactic Acid)s

Poly(lactic acid) is the subject of considerable commercial development by a variety of organizations around the world. In this work, the thermal and rheological properties of two commercial-grade poly(lactic acid)s (PLAs) are investigated. A comparison of the commercial samples to a series of well-defined linear and star architecture PLAs provides considerable insight into their flow properties. Such insights are valuable in deciding processing strategies for these newly emerging, commercially significant, biodegradable plastics. Both a branched and linear grade of PLA are investigated. The crystallization kinetics of the branched polymer are inferred to be faster than the linear analog. Longer relaxation times in the terminal region for the branched material compared to the linear material manifests itself as a higher zero shear rate viscosity. However, the branched material shear thins more strongly, resulting in a lower value of viscosity at high shear rates. Comparison of the linear viscoelastic spectra of the branched material with the spectra for star PLAs suggests that the branched architecture is characterized by a span molecular weight of approximately 63,000 g/mol. The present study conclusively demonstrates that a wide spectrum of flow properties are available through simple architectural modification of PLA, thus allowing the utilization of this important degradable thermoplastic in a variety of processing operations.     

Chemical recycling of waste Poly Vinyl Chloride (PVC) by the liquid-phase treatment

Journal of Material Cycles and Waste Management - Liquid-phase treatment of waste Poly Vinyl Chloride (PVC) was performed. Chlorine change rate was high when using alcohol, cresol and terpene...     

Estimation on Biodegradability of Poly (3-hydroxybutyrate-<Emphasis Type="Italic">co</Emphasis>-3-hydroxyvalerate) (PHB/V) and Numbers of Aerobic PHB/V Degrading Microorganisms in Different Natural Environments

To assess the capacity of the natural environment for degrading PHB/V, the film-MPN method proposed previously was modified to estimate the numbers of PHB/V degrading microorganisms (degraders) in various environments. The First-Order Reaction (FOR) model was used to determine the appropriate incubation period for the method. Numbers of aerobic PHB/V degraders were estimated in garden soil, paddy field soil, farm soil, river bank soil, infertile garden soil, river water, activated sludge, and seawater by the film-MPN method. Results were compared with those estimated by the clear-zone technique and showed that the film-MPN method was suitable for estimating the numbers of PHB/V degraders in the environments tested. On the other hand, biodegradability of injection molded PHB/V samples was investigated in several kinds of environments. The changes of weight were studied and results showed that biodegradability of PHB/V related to the numbers of PHB/V degraders in similar ecosystem in different regions. In different environments the biodegradability of PHB/V not only related to the number of PHB/V degraders, but also depended on whether there were conditions for the PHB/V degraders to grow and proliferate easily in the environment.     

Construction, Characterization and Biological Activity of Chiral and Thermally Stable Nanostructured Poly(Ester-Imide)s as Tyrosine-Containing Pseudo-Poly(Amino Acid)s

In this paper we studied the synthesis of biodegradable optically active poly(ester-imide)s containing different amino acid residues in the main chain. These pseudo-poly(amino acid)s were synthesized by polycondensation of N,N′-(pyromellitoyl)-bis-l-tyrosine dimethyl ester as a diphenolic monomer and two chiral trimellitic anhydride-derived diacid monomers containing s-valine and l-methionine. The direct polycondensation reaction of these diacids with aromatic diol was carried out in a system of tosyl chloride (TsCl), pyridine (Py) and N,N′-dimethylformamide (DMF) as a condensing agent. The structures and morphology of these polymers were studied by FT-IR, ¹H-NMR, powder X-ray diffraction, field emission scanning electron microscopy (FE-SEM), specific rotation, elemental and thermogravimetric analysis (TGA) techniques. TGA profiles indicate that the resulting PEIs have a good thermal stability. Morphology probes showed these polymers were noncrystalline and nanostructured polymers. The monomers and prepared polymers were buried under the soil to study the sensitivity of the monomers and the obtained polymers to microbial degradation. The high microbial population and prominent dehydrogenase activity in the soil containing polymers showed that the synthesized polymers are biologically active and microbiologically biodegradable. Wheat seedling growth in the soil buried with synthetic polymers not only confirmed non-toxicity of polymers but also showed possibility of phyto-remediation in polymer-contaminated soils.     

Lactic Acid Production by Hydrolysis of Poly(Lactic Acid) in Aqueous Solutions: An Experimental and Kinetic Study

Poly(lactic acid) (PLA) is increasingly utilized as an alternative to petroleum-based polymers in order to reduce their impact on the environment. The monomer of PLA is mainly produced from corn, which, in addition to its food utilization, can be also used for the production of bioethanol or biofuels. In this work the depolymerization (chemical recycling) of PLA pellets in a batch reactor at temperatures near the melting temperature of solid PLA has been investigated to produce lactic acid. New experimental data are presented and a kinetic model is provided for a first analysis. With a residence time less than 120 min, a yield of lactic acid greater than 95 % has been obtained at temperatures of 160 and 180 °C for pressure equal to water vapour pressure and a water/PLA ratio by weight equal ~10.     

Effect of Poly(l-Lactide) and Poly(Butylene Succinate) on the Growth of Red Pepper and Tomato

Seeds of red pepper and tomato were sowed and cultivated in a soil blended with powdery poly(l-lactide) (PLLA), and poly(butylene succinate) (PBS). PBS depressed the growth of the two plants significantly even at a concentration as low as 5%, whereas PLLA up to 35% affected negligibly or even boosted the growth of the two plants. pH and number of microbial cells in the soil after 80 days of cultivation were almost the same independently whether the soil was blended with the two polymers or not. In contrast, the molecular weight of PBS decreased much faster than that of PLLA. Because succinic acid and 1,4-butane diol, from which PBS was synthesized, exhibited toxicity to both plant and animal cells to retard the germination rate of young radish seeds and to deform the morphology of HeLa cells significantly [1], the monomers and the oligomers produced from the PBS degradation should have a detrimental influence on the growth of the two plants.     

Compostability of Poly(lactide): Degradation in an Inert Solid Medium

Commercial poly(lactide) degradation was studied in an inert solid medium simulating compost conditions, with the aim to achieve a complete carbon balance of the polymer degradation. The mineralisation rate at the end of the test was compared to those obtained for poly(lactide) degradation in compost. It was shown that the mineralisation rate after 45 days of degradation was quite lower in inert solid medium than in compost but the standard deviation of data was enhanced. A protocol for both extraction and quantification of the carbon included in the different degradation by-products was proposed and the carbon balance of the polymer degradation was followed during the test with a satisfactory accuracy. The non-degraded PLA material was recovered during the test, hence the evolution of the glass transition temperature and the molecular weight was followed. A two-step degradation mechanism was highlighted in inert solid medium, showing the fundamental role of abiotic reactions for PLA degradation in compost.     

Influence of Technological Process on Biodegradation of PVA/Waxy Starch Blends in an Aerobic and Anaerobic Environment

Improving biodegradability of PVA/starch blends is a reality already documented by a number of works. Admittedly, mechanical properties of products (for example, tensile strength) are somewhat worse, but suitable composition optimizing or chemical modifying of starch may eliminate the problem to a large degree. This work is an attempt to find another potential effect influencing biodegradability, that of technological procedure for producing films from these blends on an extruder. The procedure with a so-called pre-extrusion step (two-stage) and dry-blend (single-stage) produced blends of slightest differences in achieved biodegradability (virtually within limits of experimental error) in aerobic (76 vs. 79%) as well as anaerobic breakdown (48 vs. 52%). Conversely, morphological analysis exhibited superior homogeneity of films prepared by the two-stage process; their tensile strength was also higher.