Biodegradable materials — Present situation and future perspectives

Biodegradable polymers constitute a loosely defined family of polymers that are designed to degrade through the action of living organisms. They offer a possible alternative to traditional nonbiodegradable polymers if recycling is impractical or not economical. The main driving force behind this technology is the solid waste problem, particularly with regard to the decreasing availability of landfills, the litter problem and the pollution of marine environment by non-biodegradable plastics. Technologies like composting used for the disposal of food and yard waste are the most suitable for the disposal of biodegradable materials. European Standardisation Committee (CEN), Organic Reclamation and Composting Association (ORCA) and German Institute for Standardisation (DIN) have already defined, at a draft level, the basic requirements for a product to be declared compostable. They are based on: complete biodegradability of the product in a time period compatible with composting, measured through respirometric tests (ASTM D5338-9, ISO/CD14855, etc); disintegration of the material during the fermentation phase; no negative effects on compost quality; checking of laboratory-scale results on pilot/full-scale composting plants. These requirements set forth a common base for a universal marking system to readily identify products to be composted. Thermoplastic starch-based polymers and aliphatic polyesters are the two classes of biodegradable materials with the greatest near-term potential. This paper reviews a great variety of properties, structures and biodegradation behaviour of thermoplastic starch in combination with poly(vinyl alcohol) or some aliphatic polyesters like poly(hydroxybutyrate-co-hydroxyvalerate), poly(lactic acid), poly(ϵ-caprolactone) and poly(butanediyl succinate).     

Development of an automatic laboratory-scale respirometric system to measure polymer biodegradability

An automatic direct measurement respirometric system was built, calibrated and tested to determine polymer biodegradation under simulated environmental conditions. The amount of carbon dioxide produced during biopolymer biodegradation was converted to percentage of mineralization, and used as an indicator of the polymer biodegradation. Poly(lactide) (PLA) bottles were used as the test material, and the results were compared with those from corn starch powder and poly(ethylene terephthalate) (PET) bottles. The respirometric system ran for more than 63 days without any user intervention, very stable and efficiently. At 63 days of exposure at 58±2 °C and 55±5% relative humidity, PLA, corn starch, and PET achieved 64.2±0.5%, 72.4±0.7%, and 2.7±0.2% mineralization, respectively. Based on ASTM D 6400 and ISO14855, PLA bottles qualify as biodegradable since mineralization was greater than 60%.     

Biodegradation of poly(lactic acid) powders proposed as the reference test materials for the international standard of biodegradation evaluation methods

The methods for producing reference test materials for biodegradation evaluation tests have been studied. Mechanical crushing at low temperature of polymer pellets using dry ice was selected for the method of producing polymer powder of poly(lactic acid) (PLA). The powders were fractionated using 60 mesh (250 μm) and 120 mesh (125 μm) sieves. The size distributions were then measured. The average diameter of the PLA particles obtained by this method was 214.2 μm. The biodegradation speeds of these PLA polymer powders were evaluated by two methods based on the international standard and one in vitro method based on the enzymatic degradation. First, the degree of biodegradation for this PLA powder was 91% for 35 days in a controlled compost determined by a method based on ISO 14855-1 (JIS K6953) at 58 °C managed by the Mitsui Chemical Analysis and Consulting Service, Inc. (Japan). Second, these polymer powders were measured for biodegradation by the Microbial Oxidative Degradation Analyzer (MODA) in a controlled compost at 58 °C and 70 °C based on ISO/DIS 14855-2 under many conditions. The degree of biodegradation for this PLA powder was approximately 80% for 50 days. In addition, the polymer powders were biodegraded by Proteinase K which is a PLA degradation enzyme. This polymer powder was suitable as a reference material for the evaluation methods of biodegradation.     

改性淀粉材料生物降解性分析体系的建立及应用

测定了热塑性淀粉(TPS)和热塑性双醛淀粉(TPDAS)在堆肥条件下的生物降解能力。根据ISO 14855建立了一套新的测试体系并且验证了这个体系测定高分子材料生物降解性能的可行性。对热塑性淀粉材料生物降解性的测试结果发现化学改性对于淀粉的降解速率和降解速度都有很大的影响。在可控堆肥条件下TPS比TPDAS降解的要快。TPDAS的降解速度和最终的生物降解百分率和双醛淀粉(DAS)的氧化度有密切的关系。文中讨论了存在这种关系的可能原因。有不同降解速率的TPS和TPDAS的降解过程呈现出三个阶段,即迟滞阶段。降解阶段和平稳阶段。     

Cellulose acetate butyrate as multifunctional additive for poly(butylene succinate) by melt blending: Mechanical properties, biomass carbon ratio, and control of biodegradability

We have evaluated the plasticizing effect of poly(butylene succinate) (PBS) and cellulose acetate butyrate (CAB). PBS and CAB were mixed with a melt-kneading machine. The tensile strength and strain at break in the case of the blend with 10% CAB in the PBS matrix were 547% and 35 MPa. It showed that CAB acted as a plasticizer for PBS. The biomass carbon ratio of the blends measured by accelerator mass spectrometry based on ASTM D6866 showed that the biomass carbon derived from a part of the CAB corresponded to the theoretical value of the polymer blend. The biodegradation of PBS with the CAB melt blend powders was evaluated by a microbial oxidative degradation analyzer under controlled compost conditions based on ISO 14855-2. PBS with 10% CAB was not degraded within 60 days due to the addition of CAB that could control the biodegradability of the PBS.     

Aerobic and anaerobic biodegradability of polymer films and physico-chemical characterization

Aerobic and anaerobic biodegradation of four different kinds of polymers, polylactic acid, polycaprolactone, a starch/polycaprolactone blend (Mater-bi^®) and poly(butadiene adipate-co-terephthalate) (Eastar bio^®) has been studied in the solid state under aerobic conditions and in the liquid phase under both aerobic and anaerobic conditions.Several standard test methods (ISO 14851, ISO 14853, ASTM G 21-90 and ASTM G 22-76 and NF X 41-514) were used to determine the biodegradability. To determine the efficiency of the biodegradation of polymers, quantitative (mass variations, oxygen uptake, pressure variations, biogas generation and composition, biodegradation percentages) and qualitative (variation of T_g and T_f, variation of molar mass by SEC, characterization by FTIR and NMR spectroscopy) analyses were made and materials were characterized before and after 28 days of degradation.After 28 days, the degradation of materials depends on the material and on the test conditions used. The degradation is better under aerobic conditions, in particular for Mater-bi and polycaprolactone. Nevertheless, we can notice that it is the amorphous part of the polymer which is more attacked by the micro-organisms but, after 28 days, they do not seem to cleave macromolecules inside the material: bacteria attack the surface of the polymer and seem to consume the macromolecules one after another (there is no significant variation in the molar mass and no difference between FTIR and NMR spectra before degradation and after 28 days of degradation).     

聚丁二酸丁二醇酯在堆肥条件下的生物降解性能研究

根据ISO 14855的检测方法,研究了聚丁二酸丁二醇酯(PBS)在堆肥条件下的生物降解性能,结果 表明PBS具有良好的生物降解性,且其形态对其降解速率有显著的影响,降解速率:PBS粉末>PBS片>PBS 颗粒。对堆肥中的微生物进行分离鉴定,在所选堆肥中主要分离出四种菌株:杂色曲霉菌、青霉菌、芽包杆菌 和直杆高温多孢菌,它们对PBS的降解能力各不相同,其中最有效降解PBS的菌株是杂色曲霉菌。     

Biodegradation of chemically modified wheat gluten-based natural polymer materials

Biodegradation of a series of chemically modified thermally processed wheat gluten (WG)-based natural polymers were examined according to Australian Standard (AS ISO 14855). Most of these materials reached 93-100% biodegradation within 22 days of composting, and the growth of fungi and significant phase deformation were observed during the process. Chemical crosslinking did slow down the rate or reduce the degree of the biodegradation with different behaviours for different modified systems. The segments containing structures derived from the reactions with additives such as tannin or epoxidised soybean oil remained in the degradation residues while the glycidoxypropyl trimethoxysilane agent produced ∼20% un-degraded residues containing silicon-crosslinking structures. The biodegradation rate of each component of the materials was also different with the protein and starch components degraded fast but lipid degraded relatively slowly.     

Biodegradation behaviour of poly(lactic acid) and (lactic acid-ethylene glycol-malonic or succinic acid) copolymers under controlled composting conditions in a laboratory test system

(Lactic acid, ethylene glycol, malonic or succinic acid) copolymers [(LA-EG-MA) and (LA-EG-SA) copolymers] were synthesized with different monomer feed ratios by direct polycondensation. The copolymers were characterized in terms of various properties such as acid value and number average molecular weight. The aerobic biodegradation under controlled composting conditions of commercially available and laboratory synthesized poly(l-lactic acid) (PLA) and synthesized copolymers was carried out according to ISO 14855-1:2005. The biodegradability of tested materials was found to be strongly dependent on the lactic acid content, ranging from 94% (method A) and 104% (method B) to 43% (method A) and 46% (method B) over the 110-days of the 50 °C composting.     

Influence of Organophilic Ammonium-Free Nanoclay Incorporation on Mechanical Properties and Biodegradability of Biodegradable Polyester

Summary: Disposal of petroleum-derived polymers is a growing global environmental problem of alarming proportions, which has increased interest in the use and production of biodegradable materials. In addition to biodegradation, investment in research and development in the nanotechnology area is also significant. This study evaluated the effect of incorporation of an organophilic nanoclay ammonium-free salt (Novaclay™) on the mechanical properties and biodegradation of a biodegradable polyester (Ecoflex®), according to ASTM G 160. Ecoflex with and without incorporated Novaclay was characterized before and after biodegradation in organically enriched soil for up to 180 days, by visual analysis, optical microscopy, weight loss, differential scanning calorimetry, dynamic mechanical analysis, mechanical testing, and scanning electron microscopy. The pure Ecoflex and the Ecoflex/Novaclay nanocomposite were partially biodegraded by the method used, and showed changes in their morphological and mechanical properties.     

Biodegradability of polylactide bottles in real and simulated composting conditions

As new biodegradable polymers and their packaging applications are emerging, there is a need to address their environmental performance. In particular, there is a need to understand the time required for their complete disintegration, before these materials are deployed in commercial composting processes. Standards developed by ASTM and ISO evaluate the biodegradation of biodegradable plastic materials in simulated controlled composting conditions. However, a more detailed understanding of the biodegradation of complete packages is needed in order to have a successful composting operation. This paper investigates the biodegradation performance of polylactide (PLA) bottles under simulated composting conditions according to ASTM and ISO standards, and these results are compared with a novel method of evaluating package biodegradation in real composting conditions. Two simulated composting methods were used in this study to assess biodegradability of PLA bottles: (a) a cumulative measurement respirometric (CMR) system and (b) a gravimetric measurement respirometric (GMR) system. Both CMR and GMR systems showed similar trends of biodegradation for PLA bottles and at the end of the 58th day the mineralization was 84.2±0.9% and 77.8±10.4%, respectively. PLA bottle biodegradation in real composting conditions was correlated to their breakdown and variation in molecular weight. Molecular weight of 4100 Da was obtained for PLA bottles in real composting conditions on the 30th day. The biodegradation observed for PLA bottles in both conditions explored in this study matches well with theoretical degradation and biodegradation mechanisms; however, biodegradation variability exists in both conditions and is discussed in this paper.     

Biodegradation and thermal decomposition of poly(lactic acid)-based materials reinforced by hydrophilic fillers

The effect of hydrophilic fillers (starch and wood-flour) on the degradation and decomposition of poly(lactic acid) (PLA) based materials was investigated. Biodegradation was evaluated by composting under controlled conditions in accordance with AS ISO 14855. Thermal decomposition was studied by thermogravimetry (TGA). Morphological variations during biodegradation were investigated by SEM examination. It was found that biodegradation rates of PLA/starch blends and PLA/wood-flour composites were lower than that of pure cellulose but higher than that of pure PLA. The biodegradation rate was increased from about 60% to 80% when the starch content was increased from 10% to 40% after 80 days. Both starch and wood-flour accelerated thermal decomposition of PLA, and starch exhibited a relatively stronger affect then wood-flour. The decomposition temperature of PLA was decreased about 40 °C when the filler content was increased to 40%. Small polar molecules released during thermal decomposition of starch and wood-flour were attributed to the thermal decomposition behaviours of the PLA based blends and composites and their role is further discussed in this paper.     

Novel evaluation method of biodegradabilities for oil-based polycaprolactone by naturally occurring radiocarbon-14 concentration using accelerator mass spectrometry based on ISO 14855-2 in controlled compost

The biodegradabilities of poly(?-caprolactone) (PCL) powders (av. size = 180.7 μm) in controlled compost at 58 °C have been studied using the microbial oxidative degradation analyzer (MODA) based on ISO 14855-2 entitled “Determination of the ultimate aerobic biodegradability of plastic materials under controlled composting conditions - Method by analysis of evolved carbon dioxide - Part 2: Gravimetric measurement of carbon dioxide evolved in a laboratory-scale test”. The biodegradability of the PCL powders was 101.4% in a 56-day test period by the ISO method. The biodegradabilities of PCL powders have been studied using percent modern carbon (pMC) measured by accelerated mass spectrometry (AMS). Trapped CO₂ was analyzed by AMS to determine the pMC (sample) using ¹⁴C radiocarbon concentration. By using the theory that the pMC (sample) was the sum of pMC (compost) (104.88%) and pMC (PCL) (0%) as the respective ratios in the determined period, CO₂ (respiration) was calculated only from one reaction vessel. The biodegradability of PCL powders was 79.9% in a 56-day test period by the AMS method. It was found that respiration activities in the sample vessel including PCL, compost and sea sand were the same as that in the blank vessel including compost and sea sand without PCL during the active biodegradation period (0-33 day) at 58 °C. It was confirmed that respiration activities in the sample vessel were slightly higher than that in the blank vessel after active biodegradation due to the propagation of microorganisms using energy and metabolites by PCL biodegradation during those periods.     

Synthesis of poly(lactide‐ran‐MOHEL) and its biodegradation with proteinase K

Homopoly(L ‐lactide) and homopoly(D,L ‐lactide) were almost inert for biodegradation with tricine buffer or normal enzymes such as bromelain, pronase, and cholesterol esterase but biodegradable with proteinase K. Significantly enhanced biodegradation was observed when an optically active (R)‐ or (S)‐3‐methyl‐4‐oxa‐6‐hexanolide (MOHEL) unit was introduced into poly(L ‐lactide) [poly(L ‐LA)] or poly(D,L ‐lactide) [poly(D,L ‐LA)] sequences. Poly[L ‐LA‐ran‐(R)‐MOHEL] in molar ratios of 86/14 to 43/57 showed good biodegradability that was independent of crystallinity. The biodegradation of polymers with proteinase K increased in the following order: poly[D,L ‐LA‐ran‐(R)‐MOHEL] > poly[L ‐LA‐ran‐(R)‐MOHEL] > poly[D,L ‐LA‐ran‐(S)‐MOHEL] > poly[L ‐LA‐ran‐(S)‐MOHEL] > poly(R)‐MOHEL > poly(D,L ‐LA). The number‐average molecular weight, molecular weight distribution, glass‐transition temperature, and melting temperature did not change before and after the biodegradation of poly[L ‐LA‐ran‐(R)‐MOHEL], indicating that the degradation occurred from the polymer surface. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1374–1381, 2001     

Investigation of fungal deterioration of synthetic paint binders using vibrational spectroscopic techniques

The deterioration of synthetic polymers caused by biological process is usually evaluated by visual inspection and measuring physical effects. In contrast to this approach, we have applied vibrational spectroscopies to study the biodegradation of the synthetic resins. 29 synthetic resins used as paint binding media, including acrylic, alkyd and poly(vinyl acetate) polymers, were examined for potential susceptibility to fungal degradation using the standard method ASTM G21-96(2002). In addition, the degraded resins were analysed by Raman spectroscopy, FT-IR and FT-IR photoacoustic spectroscopy. Almost all the acrylic resins studied proved to be resistant to microbial attack, while all alkyd resins and some poly(vinyl acetates) turned out to be biodegradable. Within a few days of inoculation Aspergillus niger was the most copious fungus on the biodegraded resins. A comparison of the IR and Raman spectra of control and biodegraded resins did not show any differences, but photoacoustic spectroscopy revealed additional bands for the fungal-degraded resins, consistent with the presence of fungal-derived substances. The additional bands in the photoacoustic spectra were due to the presence of Aspergillus niger and melanin, a fungal pigment. Since IR photoacoustic spectroscopy can be also a suitable technique for the chemical characterisation of binding media, the same spectroscopic analysis can be employed to both characterise the material and obtain evidence for fungal colonization. Microbial growth on Sobral 1241ML (alkyd resin) after 28 d (growth rating 4) compared with the non-inoculated resin.     

Compostable Films of Mater-Bi Z Grades

Abstract

This paper focuses on the composting behavior of Mater-Bi Z grades for filming and on their in-use behavior, mainly as composting bags for the collection of organic waste. The compostability of Mater-Bi Z grades was demonstrated by means of a three-step test by following the approach of different international committees working on this matter comprising lab tests (biodegradability tests such as ASTM D 5338, ASTM 5901, and terrestrial toxicity tests) and full-scale composting tests. In addition to their compostability, the in-use behavior was estimated by tests of separate collection of organic wastes in different municipalities (Furstenfeldbruck/Bavaria, Korneuburg/Austria) comparing paper bags with Mater-Bi bags.     

Bioplastic biodegradation activity of anaerobic sludge prepared by preincubation at 55 °C for new anaerobic biodegradation test

The new method to evaluate the anaerobic biodegradability of bioplastics, such as polycaprolactone (PCL) and poly (lactic acid) (PLA), under aquatic (slurry) conditions at 55 °C is applying. For this method, we prepared the sludge at 55 °C from the sludge at 37 °C by the method in which the sludge from the real tank operating at around 37 °C using cow manure and vegetable waste as the feed stock was preincubated at 55 °C. It was unknown at which stage the sludge during preincubation has the optimized anaerobic biodegradation activity of plastics. Four different stage sludges during preincubation (the sludge at 7 days after the start of preincubation at 55 °C, at 12 days, at 18 days, and at 40 days) were compared by the anaerobic biodegradation activity of PLA. The preincubated sludge at around 18 days (a gradual decrease in biogas evolution and a methane ratio over 60%) showed the highest biodegradation activity of PLA. In addition, the bacterial population in each sludge was analyzed by the denaturing gradient gel electrophoresis (DGGE) analysis of the amplified 16S rRNA gene fragments, however, the newly grown bacteria bands at 55 °C were not clearly detected.     

Determination of crack growth kinetics in non-reinforced semi-crystalline thermoplastics using the linear elastic fracture mechanics (LEFM) approach

The aim of this study was to find a satisfactory method to characterize the fatigue crack growth behavior of non-reinforced, semi-crystalline thermoplastic polymers using linear elastic fracture mechanics (LEFM). For this, crack growth curves (crack length versus cycle number) as well as crack growth kinetics curves (crack growth rate da/dN versus amplitude stress intensity factor ΔK) had to be generated. As methods suggested by ISO 15850 and ASTM E 647-11 failed to provide satisfactory results for the crack growth curves, a more advanced method was searched for and finally found in the literature. Regarding the crack growth kinetics curve, the idea of the calculation was based on methods recommended in ISO 15850 and ASTM E 647-11. However, these methods had to be considerably modified and improved in order to get accurate results with little scatter. The whole methodology was developed and verified with fatigue crack growth tests on two semi-crystalline thermoplastics (polyoxymethylene POM and polyetheretherketone PEEK).     

Comparison of permeation resistance of protective gloves to organic solvents with ISO, ASTM and EN standard methods

In this study, the permeation resistance of nitrile and neoprene gloves to benzene and 1,2-dichloroethane was investigated using two permeation cells according to the ISO 6529, ASTM F739, and EN 374-3 standard test methods. The permeability coefficients were found to significantly increase with the flow rate of the collection medium. The appropriate flow rate of nitrogen collection should be higher than 75 and 150 mL/min for the ISO 6529 and ASTM F739 cells, respectively. For an open-loop system, the permeability coefficient of the ISO 6529 cell was obviously greater than that of the ASTM F739 cell, and the difference between these two cells was statistically significant. On the other hand, the breakthrough time was about 20–30 min for either the ISO 6529 or ASTM F739 cell at different flow rates of nitrogen collection. Fick's diffusion coefficient and solubility of permeant in the polymer glove can be specified as alternative test results for standard methods.     

多轴冲击不同测试方法下测试结果的比较

采用ISO 6603-2标准和ASTM D3763标准对多轴冲击测试中的挠度、载荷及能量进行了研究.结果表明,在不同冲击速度条件下分别采用ASTM D3763标准和ISO 6603-2标准测出的挠度、载荷及能量变化规律一致,即速度越小,挠度、能量越大,载荷越小;在相同冲击速度条件下采用ASTM D3763标准测出的撞击点挠度比采用ISO 6603-2标准测定值的大,载荷及能量比采用ISO 6603-2标准测定值小.