Biodegradation of Injection Molded Starch-Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) Blends in a Natural Compost Environment

Injection molded specimens were prepared by blending poly (hydroxybutyrate-co-valerate) (PHBV) with cornstarch. Blended formulations incorporated 30% or 50% starch in the presence or absence of poly-(ethylene oxide) (PEO), which enhances the adherence of starch granules to PHBV. These formulations were evaluated for their biodegradability in natural compost by measuring changes in physical and chemical properties over a period of 125 days. The degradation of plastic material, as evidenced by weight loss and deterioration in tensile properties, correlated with the amount of starch present in the blends (neat PHBV < 30% starch < 50% starch). Incorporation of PEO into starch-PHBV blends had little or no effect on the rate of weight loss. Starch in blends degraded faster than PHBV and it accelerated PHBV degradation. Also, PHBV did not retard starch degradation. After 125 days of exposure to compost, neat PHBV lost 7% of its weight (0.056% weight loss/day), while the PHBV component of a 50% starch blend lost 41% of its weight (0.328% weight loss/day). PHB and PHV moieties within the copolymer degraded at similar rates, regardless of the presence of starch, as determined by ¹H-NMR spectroscopy. GPC analyses revealed that, while the number average molecular weight (Mn) of PHBV in all exposed samples decreased, there was no significant difference in this decrease between neat PHBV as opposed to PHBV blended with starch. SEM showed homogeneously distributed starch granules embedded in a PHBV matrix, typical of a filler material. Starch granules were rapidly depleted during exposure to compost, increasing the surface area of the PHBV matrix.     

Aging properties of extruded high-amylose starch

The structural and mechanical properties of extruded high-amylose and normal cornstarch were studied as a function of time and humidity to determine the suitability of high-amylose cornstarch for use in biodegradable plastic materials. After extrusion at 170°C and 20–30% moisture, high-amylose starch was mostly amorphous, with small amounts of V- and A-type crystal structures. Tensile strengths for the extruded high-amylose starch ribbons were rather stable with time (65, 50, and 35 MPa at 20, 50, and 80% RH) and were higher than those for normal cornstarch (25, 40, and 15 MPa after 84 days at 20, 50, and 80% RH). Elongations at break declined gradually with time for high-amylose starch (6, 11, and 11% after 84 days at 20, 50, and 80% RH), while rapid declines were seen for normal cornstarch at higher humidities (3, 9, and 3% after 84 days at 20, 50, and 80% RH). Differential scanning calorimetry revealed that normal cornstarch aged at a high humidity had much larger sub-T _g endotherms than high-amylose cornstarch. These endotherms reflect decreases in enthalpy and free volume which occur in amorphous polymers due to structural relaxation. It appears, therefore, that plastic materials prepared from gelatinized or melted high-amylose cornstarch should have greater strength and flexibility and slower physical aging than those prepared from gelatinized normal cornstarch.Paper presented at the Bio/Environmentally Degradable Polymer Society—Second National Meeting, August 19–21, 1993, Chicago, Illinois.Product names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable.     

Comparison of compostable bags and aerated bins with conventional storage systems to collect the organic fraction of municipal solid waste from homes. A Catalonia case study

The separation of biowaste at home is key to improving, facilitating and reducing the operational costs of the treatment of organic municipal waste. The conventional method of collecting such waste and separating it at home is usually done by using a sealed bin with a plastic bag. The use of modern compostable bags is starting to be implemented in some European countries. These compostable bags are made of biodegradable polymers, often from renewable sources. In addition to compostable bags, a new model of bin is also promoted that has a perforated surface that, together with the compostable bag, makes the so-called “aerated system”. In this study, different combinations of home collection systems have been systematically studied in the laboratory and at home. The results obtained quantitatively demonstrate that the aerated bin and compostable bag system combination is effective at improving the collection of biowaste without significant gaseous emissions and preparing the organic waste for further composting as concluded from the respiration indices. In terms of weight loss, temperature, gas emissions, respiration index and organic matter reduction, the best results were achieved with the aerated system. At the same time, a qualitative study of bin and bag combinations was carried in 100 homes in which more than 80% of the families participating preferred the aerated system.     

Biodegradation of starch-poly(β-hydroxybutyrate-co-valerate) composites in municipal activated sludge

Injection-molded composites were prepared by blending PHBV⁵ with native cornstarch (30% and 50%) and with cornstarch precoated with PEO as a binding agent. These composites were evaluated for their biodegradability in municipal activated sludge by measuring changes in their physical and chemical properties over a period of 35 days. All composites lost weight, ranging from 45 to 78% within 35 days. Interestingly, the extent and rate of weight loss were quite similar in PHBV composites with no starch, with 30% starch, and with 50% starch. Weight loss was slowest in PHBV blends prepared with PEO-coated starch. For all samples, the weight loss was accompanied by a rapid deterioration in tensile strength and percentage elongation. The deterioration of these mechanical properties exhibited a relative rate of PHBV>starch-PHBV>PEO-coated starch-PHBV. Changes in starch/PHBV composition after biodegradation were quantified by FTIR spectroscopy. Increasing the starch content resulted in more extensive starch degradation, while the PHBV content in the blends became less susceptible to hydrolytic enzymes.The mention of firms names or trade products does not imply that they are endorsed or recommended by the U.S. Department of Agriculture over firms or similar products not mentioned. All programs and services of the U.S. Department of Agriculture are offered on a nondiscriminatory basis without regard to race, color, national origin, religion, sex, marital status, or handicap.     

A kinetic analysis of solid waste composting at optimal conditions

Six municipal solid waste (MSW) and yard waste components (food waste, mixed paper, yard waste, leaves, branches, grass clippings) were aerobically decomposed to measure the extent of decomposition under near optimal conditions. Decomposition was characterized by at least two principal stages, for most components, as was indicated by the carbon dioxide production rates. An aerobic biodegradation conceptual model is presented here based on the principle that solids hydrolysis is the rate-limiting step during solid waste composting. The mineralizable solid carbon of each solid waste component was assumed to comprise the readily, the moderately and the slowly (or refractory) hydrolysable carbons, each hydrolyzing at different rates to aqueous (water soluble) carbon. Aqueous carbon mineralizes to CO2 at rapid rates that are not rate-limiting to the process. Solids hydrolysis rate constants were calculated after fitting the experimentally determined carbon dioxide production rate data to model results. Hydrolysis rates for the readily hydrolysable carbon in all components ranged from approximately 0.06 to 0.1 d(-1); hydrolysis rates for the moderately hydrolysable carbon ranged from 0.005 to 0.06 d(-1). Leaves, branches and grass clippings did not have a readily hydrolysable carbon fraction, whilst the leaves and branches had the largest slowly hydrolysable carbon fractions (70%, 82%, respectively, of the total solid organic carbon). Grass and yard waste did not contain slowly hydrolysable carbon fractions. Food waste had the largest readily hydrolysable carbon fraction and produced the highest amount of CO2 among all substrates. Moderately hydrolysable solid carbon fractions ranged from 16% to 90% of the total solid organic carbon for all substrates used.     

Characterization of Biodegradable Composite Films Prepared from Blends of Poly(Vinyl Alcohol), Cornstarch,and Lignocellulosic Fiber

Several composite blends of poly(vinyl alcohol) (PVA) and lignocellulosic fibers were prepared and characterized. Cohesive and flexible cast films were obtained by blending lignocellulosic fibers derived from orange waste and PVA with or without cornstarch. Films were evaluated for their thermal stability, water permeability and biodegradation properties. Thermogravimetric analysis (TGA) indicated the suitability of formulations for melt processing, and for application as mulch films in fields at much higher temperatures. Composite films were permeable to water, but at the same time able to maintain consistency and composition upon drying. Chemical crosslinking of starch, fiber and PVA, all hydroxyl functionalized polymers, by hexamethoxymethylmelamine (HMMM) improved water resistance in films. Films generally biodegraded within 30 days in soil, achieving between 50–80% mineralization. Both starch and lignocellulosic fiber degraded much more rapidly than PVA. Interestingly, addition of fiber to formulations enhanced the PVA degradation.     

Determining biodegradability of plastic materials under controlled and natural composting environments

With the advent of recently promulgated Government regulations on plastics in Mauritius, a study was initiated to examine the biodegradability of two different types of plastic, namely Willow Ridge Plastics - PDQ-H additive (Plastic A) and Ecosafe Plastic - TDPA additive (Plastic B) under controlled and natural composting environments. The results obtained from the controlled composting environment showed that the cumulative carbon dioxide evolution for Plastic A was much higher than that for Plastic B. Plastic A therefore showed a higher level of biodegradation in terms of CO2 evolution than Plastic B. However, from the regression analysis, it was found that the level of CO2 varying with time fitted the sigmoid type curves with very high correlation coefficients (R2 values: 0.9928, 0.9921 and 0.9816, for reference material, inoculum and Plastic A, respectively). The corresponding F-values obtained from the ANOVA analysis together with significance levels of p<0.05 indicated that the three treatments analysed in the biodegradability experiment were significant. The other experiment was undertaken to observe any physical change of Plastics A and B as compared to a reference plastic, namely, compostable plastic bag (Mater-Bi product-Plastic C), when exposed to a natural composting environment. Thermophilic temperatures were obtained for about 3-5 days of composting and the moisture content was in the range of 60-80% throughout the degradation process. It was observed that after 55 days of composting, Plastic C degraded completely while Plastic A and Plastic B did not undergo any significant degradation. It can be concluded that naturally based plastic made of starch would degrade completely in a time frame of 60 days, whereas plastics with biodegradable additive would require a longer time.     

Biodegradation of LDPE/Modified Starch Blends Sterilized with Gamma Radiation

Blends of LDPE/modified starch were prepared, sterilized by gamma radiation and investigated with respect to their microbial degradation by a mixture of fungal strains in liquid medium after 90 days, was analyzed by carbon dioxide (CO₂) production (Sturm test). Biodegradation of blends was evaluated by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction; mechanical testing, scanning electron microscopy (SEM). The biodegradation of LDPE/modified starch blends was attributed to microbiological attack, with alterations in the chemical structure of the blend with an increase in the carbonyl and vinyl indices and the appearance of new crystalline symmetry generating a crystalline domain not existing before in the blend and decrease in the mechanical properties.     

Preparation and Characterization of Compatible and Degradable Thermoplastic Starch/Polyethylene Film

The degradability of the compatible thermoplastic starch/polyethylene film was investigated by weight loss percent (WLP), Fourier Transform Infrared (FT-IR) Spectroscopy, and Scanning Electron Microscope (SEM). The compatible film was prepared by using the particles of thermoplastic starch/polyethylene blends that were produced by one-step reactive extrusion. The weight of the film after degradation reduced more than 3% for 30 days and 4% for 60 days. The FTIR results revealed that both starch and polyethylene in the film exhibited varying degrees of degradation. SEM photographs of the films after degradation showed that starch particles in the film disintegrated into smaller particles or separated out of the film surface. Degradation studies demonstrated that the compatible thermoplastic starch/polyethylene film had increased degradability at the given degradable environment. The information implies that this film could be utilized as a degradable plastic.     

Biodegradation of Compostable Plastics in Green Yard-Waste Compost Environment

Compostable plastic materials, produced from polylactic acid (PLA), corn starch, or sugarcane, degraded in a green yard-waste compost environment. The compostable plastics claim to meet ASTM D6400 standards for biodegradation, sustainable plant growth, and eco-toxicity. Biodegradation was measured by disintegration studies over 20 weeks. The commercially available compostable products, made from PLA, sugarcane, or corn starch, biodegraded while in a commercial compost facility with other common yard waste compostable items. The PLA container, cup, and knife completely degraded in 7 weeks at a rate similar to the Avicell micro-cellulose control. The corn starch-based trash bag and sugarcane plate degraded at a similar rate as the Kraft paper control. The three materials degraded between 80% and 90% after 20 weeks.     

Biodegradation of Coproducts from Industrially Processed Corn in a Compost Environment

Information pertaining to biodegradability of renewable polymeric material is critical for the design and development of single-use biodegradable consumer products. The rate and extent of biodegradation of corn fiber, corn zein, cornstarch, distillers grain, and corn gluten meal were evaluated in compost environments under variable temperature, pH, and moisture conditions. Generally, composts with higher temperature (40°C), neutral pH (7.0), and 50%–60% moisture appeared to be ideal for corn coproduct biodegradation, particularly for corn gluten meal and corn zein. Low moisture conditions slowed biodegradation considerably, but degradation rates improved when moisture content increased up to 60%. Thereafter, increased moisture particularly slowed the degradation of corn gluten meal and corn zein, whereas cornstarch degradation remained unaffected. At low pH (4.0) and high pH (11.0) the rate of degradation of most coproducts was slowed somewhat. Cornstarch degradation was slower at pH 7.0, but degradation improved with increased temperatures. Increase in compost temperature from 25 to 40°C (in 5°C increments) also improved biodegradation of corn fiber and distillers grain. Addition of 1% urea to compost as a nitrogen source decreased the extent of biodegradation nearly 40% for corn gluten meal and corn zein, and 20% for cornstarch samples. Treatment of compost with 0.02% azide inhibited biodegradation of all coproducts, suggesting that the presence of metabolically active microbial cells is required for effective degradation of biobased materials in a compost environment.     

Potential of olive mill wastes for soil C sequestration

The present work deals with the potential of olive mill wastes as a C source for soil C sequestration strategy, which is based on the high lignocellulosic content that makes these wastes to degrade slowly during composting and after land application. A C balance was performed during the whole life cycle of two different two-phase olive mill wastes (TPOMW): C losses were calculated during the composting process and after soil application of the composting mixtures under laboratory conditions. The effect of the degree of stabilization of TPOMW on the overall C waste conservation efficiency was also evaluated. C losses after 34 weeks of TPOMW composting ranged from 40.58% to 45.19% of the initial C, whereas the amount of C evolved as CO2 after 8 months of incubation of soil amended with mature composts only represented between 20.6% and 21.9% of the added C. The total C losses considering the whole life cycle of the TPOMW showed lower losses compared to composts prepared with organic residues of different origin. Conversely to the typical behaviour of other organic wastes, the stabilisation degree of the TPOMW composting mixtures did not show any significant effect on the total C losses measured during composting and later land application. The low rate of degradation of TPOMW both during composting and after soil application makes the use of TPOMW as a C source an attractive strategy for soil C sequestration.     

LCA comparison of windrow composting of yard wastes with use as alternative daily cover (ADC)

This study compared the environmental impacts of composting yard wastes in windrows with using them in place of soil as alternative daily cover (ADC) in landfills. The Life Cycle Assessment was made using the SimaPro LCA software and showed that the ADC scenario is more beneficial for the environment than windrow composting. ADC use is also a less costly means of disposal of yard wastes. This finding applies only in cases where there are sanitary landfills in the area that are equipped with gas collection systems and can use yard wastes as alternative daily cover. Otherwise, the environmentally preferable method for disposal of source-separated yard wastes is composting rather than landfilling.     

A full-scale study of treatment of pig slurry by composting: kinetic changes in chemical and microbial properties

Since the indiscriminate disposal of pig slurry can cause not only air pollution and bad odours but also nutrient pollution of ground waters and superficial waters, composting is sometimes used as one environmentally acceptable method for recycling pig manure. The aim of this study was to evaluate the effect of composting pig slurry on its sanitation (evaluated by ecotoxicity assays and pathogen content determination), as well as to determine the effect of a carbon-rich bulking agent (wood shavings, WS) and the starting C/N ratio on the changes undergone by different chemical (volatile organic matter, C and N fractions) and microbiological (microbial biomass C, ATP, dehydrogenase activity, urease, protease, phosphatase, and beta-glucosidase activities) parameters during composting. Pig slurry mixed with bulking agent (P+WS) and the solid faction separated from it, both with (PSF+WS) and without bulking agent (PSF), were composted for 13 weeks. Samples for analysis were taken from composting piles at the start of the process and at 3, 6, 9, and 13 weeks after the beginning of composting. The total organic carbon, water soluble C and ammonium content decreased with composting, while Kjeldahl N and nitrate content increased. The nitrification process in the PSF+WS pile was more intense than in the PSF or P+WS composting piles. The pathogen content decreased with composting, as did phytotoxic compounds, while the germination index increased with compost age. Piles with bulking agent showed higher values of basal respiration, microbial biomass carbon, ATP and hydrolase activities during the composting process than piles without bulking agent.     

Earthworms and the Degradation of Lactic Acid–Based Stereocopolymers

Two lactic acid–based stereocopolymers, namely 50/50 and 96/4 L/D poly(l-lactic-co-d-lactic acids) and corresponding oligomers, were allowed to age under different conditions in order to investigate their toxicity and that of some potential degradation by-products, namely lactic acid and sodium and calcium lactates, to earthworms. Degradation characteristics in various worm-free and worm-containing media were also investigated under various conditions including direct feeding using impregnated paper or coated tree-leaves, model composting, and vermi composting. Data were compared with abiotic degradation in sterile neutral phosphate buffer. Last but not least, a novel method aimed at assessing the bioassimilation of degradable polymers and oligomers was utilized, which is based on the monitoring of weight changes of a population of starved worms when the worms are given the polymeric or oligomeric compounds as potential nutrients. The work shows that high molar mass poly(lactic acids) can be ingested by earthworms provided they are disintegrated first. However, they cannot be bioassimilated before hydrolytic degradation generates oligomers. The involvement of microorganisms in the bioassimilation is discussed.     

Degradation of starch-plastic composites in a municipal solid waste landfill

The rate and extent of deterioration of starch-plastic composites were determined over a 2-year period for samples buried in a municipal solid waste landfill. The deterioration of the starch-plastic composites following exposure was determined by measuring changes in tensile properties, weight loss, and starch content of samples retrieved from the landfill. Elongation decreases of 92 and 44% were measured for starch-plastic composite LDPE and LLDPE films, respectively, while elongation decreases of 54 and 21% were measured for their corresponding control films following 2 years of burial. Starch loss of 25% for LLDPE and 33% for LDPE starch-plastic composite films was measured following 2 years of landfill burial. Starch-plastic composites did not fragment or lose mass during the 2-year landfill burial. The limited degradation observed for the starch-plastic composites was attributed to the ineffectiveness of the prooxidant additive to catalyze the thermal oxidation of the polyethylene or polypropylene component of the starch-plastic composite under the environmental conditions present within the landfill.     

Influence of Filler Particle Size on Physical Properties and Biodegradation of Biocomposites Based on Low-Density Polyethylene and Lignocellulosic Fillers

This study examined biocomposites based on low-density polyethylene (LDPE) and lignocellulosic fillers [wood flour (WF) and oil flax straw (FS)] selecting four size fractions of each lignocellulosic material as fillers for the composites. The primary aim was to evaluate the influence of fraction size on the composites’ basic properties; to accomplish this, the composites’ mechanical properties, thermal oxidation, thermophysical characteristics, and water absorption capacity were examined. Then microphotographs of the samples were created and length-to-diameter (L/D) ratio of the fillers was calculated, finding that the L/D ratio increased with increasing particle size. The particle size influenced the oxidative degradation and water absorption processes in composites with oil flax but not in those with WF. Biodegradation tests performed on the recovered soil found that the loss of mass in composites based on LDPE and FS was higher than in the same composites with WF. Moreover, at the initial stage of composting, the biodegradation rate correlated with the size of filler particles (i.e., the larger the particles, the higher the degradation rate of the biocomposite).     

Depletion of chlortetracycline during composting of aged and spiked manures

Chlortetracycline (CTC) is one of the most important pharmaceuticals occurring in the environment. An increase of its application as feed supplement for livestock and poultry in the world leads to a substantial CTC contamination of manures, because most of the CTC is excreted to manure. The simulation experiment of aerobic composting was adopted to investigate CTC depletion in aged and spiked manure composting, and to address the extent of CTC depletion during composting. The results showed that the extractable CTC initial concentration was markedly different between the different manures, with 94.71mgkg(-1) in broiler manure and 879.6mgkg(-1) in hog manure. The concentration of extractable CTC decreased rapidly at the initial stage of composting, and subsequently declined slowly during aged and spiked manure composting. At the end of composting, more than 90% of CTC in the manure composting process (42 days) was depleted, except for hog manure composting with a removal of only 27%. The CTC half-lives were 11.0 days in broiler manure, 86.6 days in hog manure, 12.2 days in layer-hen manure (150.3mgkg(-1) CTC), 12.0 days in layer-hen manure (100.0mgkg(-1) CTC) and 4.39 days in layer-hen manure (53.10mgkg(-1) CTC), all according to the first order kinetics. The significance of experimental parameters in CTC depletion was assessed by the Pearson correlation approach. Microbial degradation of CTC was not effective from manure composting. CTC depletion was in good correlation with total organic carbon, total nitrogen, total phosphorus, C/N, N/P and total heavy metals.     

Detection of a Toxic Product Released by a Polyurethane-Containing Film Using a Composting Test Method Based on a Mineral Bed

The degradation of a film containing a 4,4diphenyl methane diisocyanate (MDI) poly(€-caprolactone)-based polyurethane was followed in a test system based on a mineral solid bed designed to facilitate analysis of break-down products released under composting conditions. The use of a mineral solid bed can help extraction and analytical procedures which could be hindered by the heterogeneous nature of compost. The fermentation conditions are typical of the composting environment and generate a powerfully degradative environment. The film fully disintegrated within 30 days of treatment. Analysis on the mineral bed extracts showed that: (i) about 40% of the initial polyurethane was still present in the bed extracts; (ii) this residue was strongly degraded in the poly(€-caprolactone) part, while the urethane part was almost completely recovered (from 80 to 95%, according to the measurement method); (iii) 4,4 diamino diphenyl methane (MDA), a very dangerous product of MDI, was released during biodegradation. The results indicate that a mineral bed can be employed to study degradation and metabolites formation in solid phase fermentation and that the MDI-based polyurethanes are not susceptible of a full degradation during composting and maintain the potential of a slow release of MDA into the environment after soil application.     

Study of Aging Characteristics of Ternary Blends of Polyethylenes—II

Six film samples of low-density polypropylene (LDPE)/linear LDPE (LLDPE)/high-density polypropylene (HDPE) with varying ratios of LDPE (20–45 ... wt%) and LLDPE (25–50 wt%) having a fixed amount of HDPE at 30 wt% were prepared by blown film extrusion technique. The samples were aged at four different temperatures, 55°, 70°, 85°, and 100°C, for four different time periods in the interval of between 150 hours and up to 600 hours. The change in the structure of various constituents and the formation of various oxygenated (peroxy and hydroperoxy) and unsaturated groups during thermo-oxidative degradation was discussed by infrared spectroscopy. The visiosity-average molecular weight was found to have decreased slowly in the initial aging hours and temperatures, whereas it decreased by 10% with its previous value tensile strength that is, 100°C when aged for 600 hours. The tensile strength of the sample first increased by 67% at 55°C and 89% at 70°C up to 450 hours, whereas the values increased by 52.5% at 85°C and 33.9% at 100°C when aged for 150 hours and then decreased. The percentage elongation at break increased by 2.7% at 55°C and 10.7% at 70°C for 150 and 300 hours of aging, respectively, whereas the percentage decreased when aged at 85°C and 100°C for up to 600 hours of aging. The values of gel content (percent) increased and initial degradation temperature decreased with aging time and temperature.