Studies on enhanced degradable plastics. III. The effect of weathering of polyethylene and (ethylene-carbon monoxide) copolymers on moisture and carbon dioxide permeability

Two enhanced-photodegradable polyethylenes were studied to determine the effect of photooxidative degradation upon transport properties. Water vapor permeability of LDPE films containing metal compound prooxidants, weathered to different extents under outdoor exposure was studied. A film made of LDPE blended with 20 wt% of polycaprolactone was also examined to determine if biodegradation over a 40-day period resulted in a measurable change in its water vapor transport characteristics. A gravimetric technique was used to study the effects of outdoor and weather-ometer exposures on the permeability of carbon dioxide of both the LDPE film and (ethylene-carbon monoxide) copolymer films. Generally, photooxidative degradation was seen to be accompanied by a change in transport characteristics of the polymer films.     

Cellulose acetate biodegradability upon exposure to simulated aerobic composting and anaerobic bioreactor environments

Cellulose acetate (CA) films with degree of substitution (d.s.) values of 1.7 and 2.5 were exposed to biologically active in-laboratory composting test vessels maintained at approximately 53 °C. The CA 1.7- and 2.5-d.s. films (thickness values of 0.5–1.0 and 2.0 mil, respectively) had completely disappeared by the end of 7- and 18-day exposure time periods in the biologically active bioreactors, respectively. The relatively small CA film weight loss observed in the poisoned control test vessels allows the conclusion that CA film erosion during the composting exposures resulted, at least in part, from biologically mediated processes. Under strictly anaerobic conditions, an active methanogenic inoculum was developed by acclimation of a sewage sludge to a synthetic municipal solid waste (SMSW) mixture at 42°C. The CA 1.7-d.s. film samples (0.5- to 1.0-mil thickness) were exposed in anaerobic serum bottles containing a 25% solids loading of SMSW in which methanogenic activity was rapidly established after introducing of the developed inoculum. For exposures of 30 days only small visually distinguishable fragments of the CA 1.7-d.s. films were recovered. In contrast, exposure of the CA 1.7-d.s. film to a poisoned control test vessel resulted in negligible weight loss. Therefore, degradation of the CA 1.7-d.s. films upon exposure to the anaerobic bioreactors was due, at least in part, to biologically mediated processes.Guest Editor: Dr. Graham Swift, Rohm & Haas.     

Degradation and mineralization of cellulose acetate in simulated thermophilic compost environments

Residual cellulose acetate (CA) films with initial degree of substitution (DS) values of 1.7 and 2.5 (CA DS-1.7 and DS-2.5) were recovered from a simulated thermophilic compost exposure and characterized by gel permeation chromatography (GPC), proton nuclear magnetic resonance (¹H NMR), and scanning electron microscopy (SEM) to determine changes in polymer molecular weight and DS and to study microbial colonization and surface morphology, respectively. During the aerobic degradation of CA DS-1.7 and CA DS-2.5 films exposed for 7 and 18 days, respectively, the number-average molecular weight (M _n) of residual polymer decreased by 30.4% on day 5 and 20.3% on day 16, respectively. Furthermore, a decrease in the degree of substitution from 1.69 to 1.27 (4-day exposure) and from 2.51 to 2.18 (12-day exposure) was observed for the respective CA samples. In contrast, CA films (DS-1.7 and DS-2.5) which were exposed to abiotic control vessels for identical time periods showed no significant changes inM _n and DS. SEM photographs of CA (DS-1.7 and DS-2.5) film surfaces after compost exposures revealed severe erosion and corresponding microbial colonization. Similar exposure times for CA films in abiotic control vessels resulted in only minor changes in surface characteristics by SEM observations. The conversion of CA DS-1.7 and DS-2.5 to CO₂ was monitored by respirometry. In these studies, powdered CA was placed in a predigested compost matrix which was maintained at 53°C and 60% moisture content throughout the incubation period. A lag phase of 10- and 25-day duration for CA DS-1.7 and DS-2.5, respectively, was observed, after which the rate of degradation increased rapidly. Mineralization of exposed CA DS-1.7 and DS-2.5 powders reported as the percentage theoretical CO₂ recovered reached 72.4 and 77.6% in 24 and 60 days, respectively. The results of this study demonstrated that microbial degradation of CA films exposed to aerobic thermophilic laboratory-scale compost reactors not only results in film weight loss but also causes severe film pitting and a corresponding decrease in chainM _n and degree of substitution for the residual material. Furthermore, conversions to greater than 70% of the theoretical recovered CO₂ for CA (DS 1.7 and 2.5) substrates indicate high degrees of CA mineralization.Guest Editor: Dr. Graham Swift, Rohm & Haas.     

Studies on enhanced degradable plastics: 1. The geographic variability in outdoor lifetimes of enhanced photodegradable polyethylenes

Studies on three types of enhanced photodegradable polyethylenes showed tensile elongation at break to be a suitable parameter for assessing disintegration due to outdoor weathering. Disintegration rates varied greatly with exposure location, with Arizona the harshest environment and Washington and New Jersey the mildest. The rate of breakdown of the enhanced degradable polyethylenes relative to unmodified plastic was termed an enhancement factor. For the materials studied, average enhancement factors generally ranged from five to fifteen. The location-dependent variability in rate parameters can be mostly explained in terms of different average radiation levels and temperatures at these locations. A duplicate exposure protocol was developed to determine if the test data were complicated by short-term fluctuations in sunlight or temperature during exposure.     

Formulation of a Photosensitized Polyethylene Film; Its Structure and Property Variation Under the Weathering Conditions of Tehran

To develop an environmentally degradable polymer material, a masterbatch pro-oxidant system was blended into low-density polyethylene. The polymer film samples were prepared by compression molding. The prepared films were placed under the natural environment of Tehran for weathering studies and accelerated conditions were also performed for UV aging in UV chamber. At different time intervals, the changes in chemical structure of photosensitized polyethylene samples were studied by FTIR and compared to that of the control polyethylene films. Also the mechanical properties of photosensitized polyethylene films were determined in comparison with the control films by measuring the tensile strength and elongation at break after exposure to the natural environment and UV radiation. Results showed that the overall rate of degradation process is clearly dependent on the polyethylene composition, test conditions (natural or accelerated), season of the year, and the duration of the weathering of the samples.     

Oxygen and Water Barrier Properties of Coated Whey Protein and Chitosan Films

Films of whey protein and chitosan acetic acid salt have lower oxygen permeability than, for example, ethylene-co-vinylalcohol under dry conditions, but water and water vapor seriously impair the gas barrier properties. To reduce the oxygen permeability at 90% relative humidity and the water-vapor transmission rate at 100% relative humidity, the films were coated with an alkyd, a beeswax compound, or a nitrocellulose lacquer. Permeability and transmission rate measurements were performed in accordance with standard methods and showed that the beeswax compound and the nitrocellulose were appropriate as water-vapor barriers. Overall migration to water was measured after 10 days exposure time, with the coated surface exposed to the water, showing that the alkyd-coated and the nitrocellulose-coated films were both below the safety limit for food contact. Water absorbency tests, performed by the Cobb method, showed that the films coated with the beeswax compound or with nitrocellulose lacquer exhibit lower absorbency than the alkyd-coated films.     

Assessment of the Whole Environmental Degradation of Oxo-Biodegradable Linear Low Density Polyethylene (LLDPE) Films Designed for Mulching Applications

The current paper is aimed at understanding the environmental fate of linear low density polyethylenes (LLDPE) films designed for mulching purposes and loaded with different pro-degradant additives. These were analyzed, upon exposure to natural sunlight for a period intended to mimick a general crop season in the mediterranean region. The selected samples underwent a relatively low extent of degradation as monitored by carbonyl index, molecular weight variation, extractability by solvent, changes in the onset of the decomposition temperature and crystallinity. The tendency to biodegradation of outdoor exposed LLDPE was then assessed under different environmental compartments including soil medium, aqueous medium as well as in axenic culture of white-rot fungus Phanerochaete chrysosporium. That fungus is known to be effective in the degradation of recalcitrant organic materials and plastic items. During the soil burial biodegradation test, lasted for 27?months, samples specimen were withdrawn at time intervals and characterized by means of structural and thermal analysis. These analytical assessments allowed to monitor any progress of oxidative degradation as a direct effect of the incubation in an active microbial environment. Analogous characterizations were carried out at the end of the biodegradation tests in aqueous medium and in P. chrysosporium axenic cultures. Data presented here are in keeping with the initial abiotic oxidation via a free radical chain reaction promoted by a pro-degradant additive acting on hydroperoxides and peroxide moieties present initially in the polymer bulk. This step was followed by a free radical cascade reactions leading to degradation once the oxidation started under relatively mild conditions (sunlight exposure). During the incubation step in soil, the abiotically degraded samples underwent significant variation in the level of oxidation and degradation with respect to the detected starting values. Indications were gained on the synergistic effect of a random fashion microbial metabolization coupled to biotically mediated oxidation of the original abiotically fragmented samples. Similar results were obtained in the biodegradation tests carried out in the aqueous media and in presence of P. chrysosporium axenic cultures. These evidences are suggesting the role of natural occurring microorganisms in promoting both partial oxiditation and degradation of LLDPE samples in combination with contextual mineralization process of the oxidized fragments.     

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.     

Analysis of Biodegradability of Three Biodegradable Mulching Films

The development of biodegradable mulching films is a great direction for environment protecting and oil saving problems. In this paper, it was used three kinds of biodegradable mulching films named a, b and c (different ratio between modified starch and poly-CL with pro-oxidant additives) in microorganism culture test and soil burial test was investigated under laboratory conditions. The index of degradation was assessed by visual observation, weight loss and SEM analysis from quantitative and qualitative aspect. The results of both tests showed that these biodegradable mulching films were more readily degraded than the common plastic film. The percentage weight loss was in sequence of biodegradable mulching film c > biodegradable mulching film b > biodegradable mulching film a, while common plastic film basically had no changes. Weight loss was not as obvious as the visual degradation and suggested broader types of microbial attack. SEM analysis clearly indicated that the changes of surface morphology of these samples after the soil burial exposure.     

Biodegradability of blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with cellulose acetate esters in activated sludge

Blends of the bacterially produced polyester poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with cellulose acetate esters (CAE) further substituted with propionyl or butyryl groups (degree of substitution: 2.60 propionyl and 0.36 acetyl or 2.59 butyryl and 0.36 acetyl, respectively) were exposed for 4 months to activated sludge to determine their biodegradability. Samples of such blends made by solution-mixing and solvent-casting had complex morphologies in which both individual components as well as a miscible blend phase were present. Additionally, the two opposite surfaces of solvent-cast films showed both physical and chemical differences. After 2 months, samples of pure PHBV had degraded by more than 98% (15 mg/cm² of surface area), whereas a pure CAE sample had degraded less than 1% (<0.2 mg/cm²). Samples containing 25% CAE lost less than 40% of their initial weights (6 mg/cm²) over the total 4-month period. Samples with 50% CAE lost up to 16% weight (2 mg/cm²), whereas those containing 75% CAE lost only slightly more weight than corresponding sterile control samples (1 mg/cm²). NMR results confirm that weight loss from samples containing 25% CAE resulted only from degradation of PHBV and that the surface of samples became enriched in CAE. Solvent-cast film samples containing equal amounts of PHBV and CAE degraded preferentially on the surface which formed at the polymer-air interface. Scanning electron microscopy and attenuated total reflectance infrared spectroscopy revealed this surface to have a rougher texture and a greater PHBV content.     

A spectrophotometric method for detection of enzymatic degradation of thin polymer films

An assay method has been developed for monitoring the enzymatic degradation of thin films of translucent polymers. The method was based on the observation that when a solution-cast film of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) was exposed to a solution of a depolymerase fromPseudomonas lemoignei, the surface of the film roughened and the film became visibly turbid. This increase in turbidity could be measured spectrophotometrically and was reproducible during the initial stage of degradation. Turbidity correlated very closely with film weight loss early in the degradation but reached a maximum value before extensive degradation had taken place. For a given set of films, this correlation was independent of the concentration of the enzyme used, although it did vary with the mode of enzyme exposure. The turbidity was associated with the exposure of crystalline domains due to the removal of amorphous material from the film surface. The increase in crystallinity at the surface was verified by attenuated total reflectance infrared spectroscopy (ATRIR). In conjunction with SEM, weight loss, and ATRIR, the film turbidity assay provided much semiquantitative insight into the mechanism of the enzymatic degradation reaction. This assay was used to study the enzymatic degradation of films of PHBV solution blended with cellulose acetate esters (CAE). The presence of only 25% of CAE of degree of substitution 2.9 severely hampered the enzymatic degradability of PHBV, a result which is consistent with the environmental degradation of these same samples exposed to activated sludge.     

Sampling strategies in the assessment of long‐term exposures to toxic substances in air

The decision to mitigate exposures from vapor intrusion (VI) is typically based on limited data from 24‐hour air samples. It is well documented that these data do not accurately represent long‐term average exposures linked to adverse health effects. Limited decision guidance is currently available to determine the most appropriate sampling strategy, considering the cost of sampling alternatives along with the economic consequences of exposure‐related health effects. We present a decision model that introduces economic and statistical considerations in evaluating alternative VI sampling methods. The model characterizes the best sampling method by factoring economic and health consequences of exposure, the variability of exposure, the cost of sampling and mitigation, and the likelihood of false‐negatives and false‐positives. Decision‐makers can use results to select the sample size that maximizes net benefit. Conceptual and mathematical models are presented linking biological, statistical, and economic considerations to assess the cost and effectiveness of different sampling strategies. The model relates an average exposure concentration, determined statistically, to abatement costs and to the monetary value of health deterioration. The value of the information provided by different strategies is calculated and used to select the optimum sampling method. Simulations show that longer‐term sampling methods tend to be more accurate and cost‐effective than short‐term samples. The ideal sampling strategy shows significant seasonal variation (it is typically optimal to use longer samples in the winter) and also varies significantly with the stringency of regulatory standards. Longer‐term sample collection provides a more accurate representation of average VI exposure and reduces the likelihood of type I and type II errors. This reduces expected costs of mitigation and exposure (e.g., health consequences, legal and regulatory penalties), which in some cases can be quite significant. The model herein shows how these savings are balanced against the additional costs of longer‐term sampling.     

Evaluation of Biodegradable Films Made of Waste Mycelium and Poly (Vinyl Alcohol) on the Yield of Pak-Choi

Novel biodegradable films were prepared via blending of poly (vinyl alcohol) and waste mycelium from sauce residue and citric acid fermentation residue, respectively. The performance of these two types of films when used as alternative covers for pak-choi growth under semi-arid climatic conditions was evaluated via field test towards their abilities for water retention and biodegradation, together with the impact on the yield and nutritional quality of pak-choi. Experimental results showed that the use of these films could result in 50% higher water retention than a blank control film after 96-h treatment at 40?°C. Films were biodegraded within 14?weeks under natural conditions, leading to a significant mineralization, progressively releasing over 56% of K⁺, NO₃ ^?, Mg²⁺ and organics, beneficial for plant growth as fertilizer. The yield of pak-choi was increased by 80% in weight when using these films compared with the unmulched control. Compared to those treated with traditional LDPE mulching film, the average contents of chlorophyll, crude protein and soluble sugar in pak-choi were increased by 52.9, 7.2, 80.7% (blends of sauce residue) and 26.7, 11.4, 10.8% (blends of citric acid fermentation residue), respectively.     

An accelerated laboratory study evaluating the disintegration rates of plastic films in simulated aquatic environments

Six plastic films were exposed to accelerated sunlight while in simulated aquatic environments to determine the effects of chemical composition and environment on the disintegration rates. An environment of UV light/no water was used as a control to determine if the microorganisms in the aquatic systems enhanced the breakdown of the plastic films. The disintegration rate of the plastics was determined by monitoring changes in selected physical properties. The plastics included two conventional plastics commonly used in packaging (LDPE and polystyrene) and four plastics enhanced to have more rapid breakdown in the environment (2% ECO, 10% ECO, PE with ketone graft, and PE with starch). The two ECO copolymers had a significantly faster loss of physical properties than the other plastics evaluated in this study. Degradation was influenced by environmental conditions. Those plastics that showed a change in physical properties had a greater change faster in the UV light/no water than in the environments where water was present. Plastics on the surface of the water showed a more rapid loss of properties than those samples partially or completely submerged. This can be attributed to decreased light intensity and the lack of heat buildup.     

Biodegradation and Ecotoxicity of Polyethylene Films Containing Pro-Oxidant Additive

The worldwide accumulation of non-degradable plastic materials, such as plastic bags, is one of the most important environmental concerns nowadays. The use of degradable materials is an option to mitigate the environmental impact generated by the consumption of plastics. One of the technologies used for the manufacture and use of degradable plastics is the use of pro-degradant additives that are incorporated in conventional plastics to promote their degradation under certain conditions. The aim of this study is to evaluate the process of oxidation, biodegradation and potential ecotoxicity of polyethylene films containing an oxo-degradable additive, according to the standard ASTM D-6954. This method establishes a procedure in which the samples are subjected to consecutive steps of accelerated oxidation, biodegradation by composting and ecotoxicity assessment. Furthermore, the effect of the presence of printing ink in the polyethylene samples with oxo-degradable additive was evaluated, and the results were compared with those obtained for samples of conventional polyethylene and polylactic acid. After 180 days of laboratory controlled composting, the samples reached the following percentages of biodegradation: polylactic acid, 41 %; printed oxo-degradable polyethylene, 32.24 %; oxo-degradable polyethylene, 25.84 %; printed polyethylene, 18.23 % and polyethylene, 13.48 %. The cellulose sample used as a control was mineralized in 58.45 %. Ecotoxicity assessment showed that the products of biodegradation of the samples tested, did not generate a negative effect on germination or development of the vegetal species studied. Under proper waste management conditions, these plastics can be used as an option to decrease the environmental impact of plastic films.     

Effects of Temperature and Relative Humidity on Polylactic Acid Plastic Degradation

Three high molecular weight (120,000 to 200,000 g mol^–1) polylactic acid (PLA) plastic films from Chronopol (Ch-I) and Cargill Dow Polymers (GII and Ca-I) were analyzed for their degradation under various temperature and relative humidity (RH) conditions. Two sets of plastic films, each containing 11 samples, were randomly hung in a temperature/humidity-controlled chamber by means of plastic-coated paper clips. The tested conditions were 28, 40, and 55°C at 50 and 100% RH, respectively, and 55°C at 10% RH. The three tested PLA films started to lose their tensile properties when their weight-average molecular weight (M _w) was in the range of 50,000 to 75,000 g mol^–1. The average degradation rate of Ch-I, GII, and Ca-I was 28,931, 27,361, and 63,025 M _w/week, respectively. Hence, GII had a faster degradation rate than Ch-I and Ca-I under all tested conditions. The degradation rate of PLA plastics was enhanced by the increase in temperature and relative humidity. This trend was observed in all three PLA plastics (Ca-I, GII, and Ch-I). Of the three tested films, Ch-I was the first to lose its mechanical properties, whereas Ca-I demonstrated the slowest loss, with mechanical properties under all tested conditions.     

Degradable polymers: The role of the degradation environment

The degradability of several degradable polymers was examined using three types of degradation environments. These include exposure in a laboratory-scale composting test system containing material representative of the organic fraction of municipal solid waste (MSW), exposure in a thermal hydrolytic environment consisting of water at 60‡C, and exposure in a thermal-oxidative, dry oven environment of 60‡C. The results of the investigation clearly indicate that, in addition to chemical and biological activity which can lead to polymer degradation, physical restructuring and reorganization of the macromolecular structure may also occur at temperatures typically found in a compost environment, resulting in changes in the mechanical properties of the polymer films. In the case of the polyethylene-modified polymers evaluated in this study, all behaved similarly, but differently from the other polymer types. The polyethylene-based films appeared to be susceptible to oxidative degradation and should degrade in a composting environment providing that there is sufficient air in contact with the film for a sufficient period of time. However, when exposed in a laboratory composter, it appears that although ideal temperature-time curves may be obtained, the test time period was insufficient in comparison to the induction period required to achieve the desired thermal oxidative degradation. Issued as NRCC No. 37620.     

Outdoor Weathering Evaluation of Carbon-Black-Filled, Biodegradable Copolyester as Substitute for Traditionally Used, Carbon-Black-Filled, Nonbiodegradable, High-Density Polyethylene Mulch Films

Carbon-black-filled, biodegradable, copolyester mulch film (Eastar®, or EA, Tennessee Eastman, Kingsport, TN) and commercial carbon-black-filled, high-density polyethylene (HDPE) mulch film were exposed for 12 weeks to commercial vegetable crop growing conditions by being placed directly on irrigated soil in the field of the University of Tennessee Alcoa Highway State Agriculture Experiment Station (Knoxville, TN) and by being placed on a plywood exposure rack as described by the American Society of Testing and Materials (ASTM) Standard Test Method 1435: Outdoor Weathering of Plastics. Mechanical properties and weather information were collected in order to evaluate the feasibility of using the newly developed biodegradable EA mulch film to replace the nonbiodegradable HDPE mulch film. Results indicate that the EA mulch film exhibited favorable tensile strength and elongation-at-break during outdoor exposure rack testing and outdoor, in-field, placed directly on the soil, exposure testing, suggesting biodegradable EA could be a substitute for the HDPE nonbiodegradable material.     

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.     

Performance of Pultruded Jute Fibre Reinforced Phenolic Composites as Building Materials for Door Frame

The pultruded jute/phenolic composites were aged under various humidity, hydrothermal and weathering conditions. Aging-induced effect of these conditions on the jute profiles was studied in terms of their physico-mechanical properties. It is observed that dimensional change of the profiles was only upto 4% even in an accelerated water aging condition. The effect of absorbed moisture/water on the jute profile was more pronounced in an accelerated water aging than the samples are being exposed to high humidity and alternate wetting and drying cycles. The changes in the values of internal bond strength of the profiles could be used as an indicator because of its sensitivity towards aging. Accentuation of fibres on the weathered samples along with severe resin erosion has suggested to layer the surface of the profiles with rich resin prior to use in the outdoor. The properties of jute profile door frame were satisfactory when compared with the requirements mentioned in IS: 4021–83 – Indian standard specification for timber door, window and ventilator frames. Performance of the installed door frame has shown no sign of dimensional instability in terms of warping and bulging after 3 years. It is suggested that jute door frames could be used as an alternative to the wooden door frames in buildings.