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%.     

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).     

A biostimulation-based accelerated method for evaluating the biodegradability of polymers

The high cost and long duration of the existing standard tests, such as ASTM D5338 and ISO 14855, represents an important drawback in evaluating the biodegradability of polymers. This works presents a new accelerated method for this purpose, based on the use of a Bartha respirometer and biostimulation with yeast extract. The new method was applied to microcrystalline cellulose (MCC), low density polyethylene (LDPE), poly(3-hidroxybutyrate) (PHB), poly(lactic acid) (PLA), poly(vinyl alcohol) (PVOH), polypropylene (PP) and poly(ethylene terephthalate) (PET). The results obtained with these polymers were consistent with those of the standard methods in terms of differentiating biodegradable and non-biodegradable polymers and relative order of biodegradation extent. Besides, a significant reduction of test duration was achieved (from 45 to 110 days with ASTM D5338 or ISO 14855 to 28 days). These results corroborate the potential of the proposed method as a fast test for assessment of biodegradation of polymeric materials.     

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.     

New insights into polylactide biodegradation from molecular ecological techniques

Molecular ecological techniques for direct identification of microbes involved in PLA degradation under aerobic composting conditions are described. Gene sequences from genera Paecilomyces, Thermomonospora, and Thermopolyspora were most abundant in the compost samples. Members of these phylogenetic lineages are therefore likely to play an important role in PLA degradation. The use of molecular ecological techniques to design cultivation strategies may also provide a new tool for identification and investigation of biodegradation mechanisms and for future development of efficient biological treatment or recycling processes for PLA and other biodegradable polymers.     

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.     

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.     

Effect of ethylene-co-vinyl acetate-glycidylmethacrylate and cellulose microfibers on the thermal,rheological and biodegradation properties of poly(lactic acid) based systems

The properties and biodegradation behavior of blends of poly(lactic acid) (PLA) and ethylene-vinyl acetate-glycidylmethacrylate copolymer (EVA-GMA), and their composites with cellulose microfibers (CF) were investigated. The blends and composites were obtained by melt mixing and the morphology, phase behavior, thermal and rheological properties of PLA/EVA-GMA blends and PLA/EVA-GMA/CF composite films were investigated as a function of the composition. The disintegrability in composting conditions was examined by means of morphological, thermal and chemical analyses to gain insights into the post-use degradation processes. The results indicated a good compatibility of the two polymers in the blends with copolymer content up to 30 wt.%, while at higher EVA-GMA content a phase separation was observed. In the composites, the presence of EVA-GMA contributes to improve the interfacial adhesion between cellulose fibers and PLA, due to interactions of the epoxy groups of GMA with hydroxyls of CF. The addition of cellulose microfibers in PLA/EVA-GMA system modifies the rheological behavior, since complex viscosity increased in presence of fibers and decreased with an increase in frequency. Disintegration tests showed that the addition of EVA-GMA influence the PLA disintegration process, and after 21 days in composting conditions, blends and composites showed faster degradation rate in comparison with neat PLA due to the different morphologies induced by the presence of EVA-GMA and CF phases able to allow a faster water diffusion and an efficient PLA degradation process.     

纤维素纤维材料几种降解方法的研究

测试和比较了天然棉纤维织物和几种人造可再生纤维素纤维(竹原纤维、莫代尔纤维和天丝纤维)在实验室条件下和大环境堆肥条件下的生物降解性.生物降解行为的测试分别采用ASTM D5988-03、堆肥法和酶催化降解法,以比较几种织物在自然环境和微生物培养基条件下的降解速度;结合红外光谱通过分析降解前后结构的改变研究不同的降解方法对纤维素材料的降解程度.结果表明纤维素类纤维织物均表现出良好的生物降解性,并且人造可再生纤维素纤维的降解速度高于天然棉纤维.和传统的实验室条件下测量织物降解性的方法相比,堆肥中含有更多的微生物和酶活性组分,加速了纤维素材料的分解.     

Biodegradable compositions by reactive processing of aliphatic polyester/polysaccharide blends

Commercially available biodegradable aliphatic polyesters, i.e., high molecular weight poly(ϵ-caprolactone) (PCL) and polylactide (PLA), were melt blended with a well-known natural and biodegradable polysaccharide: starch either as corn starch granules or as thermoplastic corn starch after plasticization with glycerol. Conventional melt blending yielded compositions with poor mechanical performances as a result of lack of interfacial adhesion between the rather hydrophobic polyester matrix and the highly hydrophilic and moisture sensitive starch phase. Interface compatibilization was achieved via two different strategies depending on the nature of the polyester chains. In case of PLA/starch compositions, PLA chains were grafted with maleic anhydride through a free radical reaction conducted by reactive extrusion. The maleic anhydride-grafted PLA chains (MAG-PLA) allowed for reinforcing the interfacial adhesion with granular starch as attested by TEM of cryofracture surface. As far as PCL/starch blends were concerned, the compatibilization was achieved via the interfacial localization of amphiphilic graft copolymers formed by grafting of PCL chains onto a polysaccharide backbone such as dextran. The PCL-grafted polysaccharide copolymers were synthesized by controlled ring-opening polymerization of ϵ-caprolactone proceeding via a coordination-insertion mechanism. These compatibilized PCL/starch compositions displayed much improved mechanical properties as determined by tensile testing as well as a much more rapid biodegradation as measured by composting testing.     

UV Protective,Antioxidant, Antibacterial and Compostable Polylactic Acid Composites Containing Pristine and Chemically Modified Lignin Nanoparticles

Polylactic acid (PLA) films containing 1 wt % and 3 wt % of lignin nanoparticles (pristine (LNP), chemically modified with citric acid (caLNP) and acetylated (aLNP)) were prepared by extrusion and characterized in terms of their overall performance as food packaging materials. Morphological, mechanical, thermal, UV–Vis barrier, antioxidant and antibacterial properties were assayed; appropriate migration values in food simulants and disintegration in simulated composting conditions were also verified. The results obtained indicated that all lignin nanoparticles succeeded in conferring UV-blocking, antioxidant and antibacterial properties to the PLA films, especially at the higher filler loadings assayed. Chemical modification of the fillers partially reduced the UV protection and the antioxidant properties of the resulting composites, but it induced better nanoparticles dispersion, reduced aggregates size, enhanced ductility and improved aesthetic quality of the films through reduction of the characteristic dark color of lignin. Migration tests and disintegration assays of the nanocomposites in simulated composting conditions indicated that, irrespectively of their formulation, the multifunctional nanocomposite films prepared behaved similarly to neat PLA.     

Plasticizing effects of epoxidized sun flower oil on biodegradable polylactide films: A comparative study

Polylactide (PLA) is one of the most promising materials among the renewable source-based biodegradable plastics. However, high inherent stiffness and brittleness of the pure PLA is often insufficient for wide range of engineering applications. One of the best ways to improve the processability, toughness and flexibility of PLA is to plasticize with epoxidized plant oils. In this work, epoxidized sun flower oil (ESFO) was incorporated into PLA matrix. The thermal, mechanical, biodegradation, optical transmission properties and fracture morphology of ESFO plasticized PLA were investigated to make a comparison with that of PLA plasticized by commercial epoxidized soya bean oil (ESO). Results show that a remarkable improvement of elongation at break was observed in the case of ESFO incorporated PLA. Although a slightly decrease the T _g of PLA was resulted from the plasticizing effects of ESFO, the thermal stability of the plasticized PLA was improved. On the other hand, the ESFO plasticized PLA showed a higher level of UV adsorption but a lower level of biodegradation ratio. After all, ESFO exhibited similar effects on the biodegradable PLA films to ESO, which is anticipated to be a good candidate for plasticizing biodegradable polymer materials.     

Biodegradation of sequentially surface treated lignocellulose reinforced polylactic acid composites: Carbon dioxide evolution and morphology

Maple fibres were treated with a variety of sequential treatments, namely sodium hydroxide (NaOH), NaOH followed by acetylation, or NaOH followed by silanation. These fibres were incorporated into a polylactic acid (PLA) composite and the biodegradation effects were investigated. After 124 days, all composites had exceeded 90% biodegradation with most close to 100%. The PLA composite with the NaOH-treated fibres had the quickest onset of degradation (4.9 days) and highest peak rate of degradation (1.77% biodegradation/day) of all composites studied. Neat PLA had a similarly high peak rate of degradation at 1.85% biodegradation/day, but had a later onset of 11 days. Gel permeation chromatography (GPC) analysis showed the earlier onset of degradation of the composites was caused by increased hydrolysis during composite fabrication as well as composting. GPC showed the formation of up to three molecular weight bands in the PLA during composting which were hypothesised to be occurring by surface hydrolysis, bulk hydrolysis and hydrolysis at the fibre interface. Analysing the remaining composite revealed the NaOH treatment not only caused an increased rate of degradation in the PLA through increase fibre porosity, but also caused an increased rate of degradation in the fibre from the lack of surface waxes and hemicellulose. Similar, yet slower, behaviours were also seen in the NaOH followed by acetylation and NaOH followed by silane treated composites with all composites degrading more rapidly than the neat PLA and neat maple fibre samples.     

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.     

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).     

3D printed polylactic acid nanocomposite scaffolds for tissue engineering applications

In this study, biodegradable polylactic acid (PLA) and PLA nanocomposite scaffolds reinforced with magnetic and conductive fillers, were processed via fused filament fabrication additive manufacturing and their bioactivity and biodegradation characteristics were examined. Porous 3D architectures with 50% bulk porosity were 3D printed, and their physicochemical properties were evaluated. Thermal analysis confirmed the presence of ~18 wt% of carbon nanostructures (CNF and GNP; nowonwards CNF) and ~37 wt% of magnetic iron oxide (Fe₂O₃) particles in the filaments. The in vitro degradation tests of scaffolds showed porous and fractured struts after 2 and 4 weeks of immersion in DMEM respectively, although a negligible weight loss is observed. Greater extent of degradation is observed in PLA with magnetic fillers followed by PLA with conductive fillers and neat PLA. In vitro bioactivity study of scaffolds indicate enhancement from ~2.9% (PLA) to ~5.32% (PLA/CNF) and ~ 3.12% (PLA/Fe₂O₃). Stiffness calculated from the compression tests showed decrease from ~680 MPa (PLA) to 533 MPa and 425 MPa for PLA/CNF and PLA/Fe₂O₃ respectively. Enhanced bioactivity and faster biodegradation response of PLA nanocomposites with conductive fillers make them a potential candidate for tissue engineering applications such as scaffold bone replacement and regeneration.     

Plasticization of poly(lactide) with blends of tributyl citrate and low molecular weight poly(d,l-lactide)-b-poly(ethylene glycol) copolymers

Polylactide (PLA) is a potential candidate for the partial replacement of petrochemical polymers because it is biodegradable and produced from annually renewable resources. Characterized by its high tensile strength, unfortunately the brittleness and rigidity limit its applicability. For a great number of applications such as packaging, fibers, films, etc., it is of high interest to formulate new PLA grades with improved flexibility and better impact properties.In order to develop PLA-based biodegradable packaging, the physico-mechanical properties of commercially available PLA should be modified using biodegradable plasticizers. To this end, PLA was melt-mixed with blends of tributyl citrate and more thermally stable low molecular weight block copolymers based on poly(d,l-lactide) and poly(ethylene glycol) of different molecular weights and topologies. The copolymers have been synthesized using a potassium based catalyst which is expected to be non toxic and were characterized by utilization of TGA, GPC and NMR techniques.The effect of the addition of up to 25 wt% plasticizer on the thermo-mechanical properties of PLA was investigated and the results were correlated with particular attention to the relationship between properties and applications.To confirm the safety of the catalyst used for the preparation of the copolymers, in vitro cytotoxicity tests have been carried out using MTS assay and the results show their biocompatibility in the presence of the fibroblast cells.Compost biodegradation experiments carried out using neat and plasticized PLA have shown that the presence of plasticizers accelerates the degradation of the PLA matrix.     

To compost or not to compost: Carbon and energy footprints of biodegradable materials’ waste treatment

Many life cycle assessments of bio-based and biodegradable materials neglect the post-consumer waste treatment phase because of a lack of consistent data, even though this stage of the life cycle may strongly influence the conclusions. The aim of this paper is to approximate carbon and energy footprints of the waste treatment phase and to find out what the best waste treatment option for biodegradable materials is by modelling home and industrial composting, anaerobic digestion and incineration. We have compiled data-sets for the following biodegradable materials: paper, cellulose, starch, polylactic acid (PLA), starch/polycaprolactone (MaterBi), polybutyrate-adipate-terephthalate (PBAT, Ecoflex) and polyhydroxyalkanoates (PHA) on the basis of an extensive literature search, experiments and analogies with materials for which significant experience has been made. During biological waste treatment, the materials are metabolised so a part of their embodied carbon is emitted into air and the remainder is stored as compost or digestate. The compost or digestate can replace soil conditioners supporting humus formation, which is a benefit that cannot be achieved artificially. Experimental data on biodegradable materials shows a range across the amount of carbon stored of these materials, and more trials will be required in the future to reduce these uncertainties. Experimental data has also shown that home and industrial composting differ in their emissions of nitrous oxide and methane, but it should be noted that data availability on home composting is limited. The results show that anaerobic digestion has the lowest footprint for the current level of technology, but incineration may become better in the future if energy efficiency in waste incineration plants improves significantly. Home composting is roughly equal to incineration with energy recovery in terms of carbon and energy footprint when carbon credits are considered. The same applies to industrial composting if carbon credits are assigned for compost to replace straw. Carbon credits can therefore considerably affect the results, but there are significant uncertainties in how they are calculated. Incineration may become better than home composting in the future if the average energy efficiency in waste incineration plants improves significantly. However, biological waste treatment options should be chosen when soil carbon is a limiting factor.     

Biodegradation of poly(lactic acid)/starch/coir biocomposites under controlled composting conditions

The aim of this work was to investigate the aerobic biodegradation of a composite under controlled composting conditions using standard test methods. Composite was formed by poly(lactic acid) (PLA), with and without the addition of maleic anhydride (MA), acting as coupling agent, thermoplastic starch (TPS) and short natural fibre (coir). For comparison its starting materials, such as TPS and matrix (containing 75 wt% of PLA and 25 wt% of TPS), were also tested.At the end of the incubation period, TPS appeared to be the most bio-susceptible material being totally biodegraded and the matrix showed a higher level of biodegradation (higher amounts of evolved CO₂) than PLA, probably due to the TPS domains preferentially attacked by microorganisms and increasing the percentage of carbon dioxide produced. Fibres seemed to play a secondary role in the process as confirmed by the slight differences in carbon dioxide produced. The compatibilised composite revealed a lower percentage of evolved CO₂ than the uncompatibilised one. Finally, the degradation results were confirmed by thermal properties' changes of tested materials at different incubation times, as monitored by thermal analysis, and by the scanning electron microscopy (SEM) analyses of the compost aged samples. SEM micrographs showed the formation of patterns and cracks on the surface of the materials aged in the compost evidencing a profound loss of structure. Moreover, an extended biofilm (evident also with optical microscopy observation) was detected on the biodegraded materials, thus indicating the growth of a large number of bacteria and fungi on their surfaces.     

Biodegradation behavior of poly(butylene adipate-co-terephthalate) (PBAT), poly(lactic acid) (PLA), and their blend under soil conditions

Poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) were mixed at a ratio of 40:60, extruded to form granules and cast into film; then, the PLA, PBAT, and PBAT/PLA film samples were buried in real soil environments. The residual degraded samples were taken regularly from the soil and analyzed by SEM, DSC, TGA, IR spectroscopy and elemental analysis. The analyses showed that PBAT and PLA had different biodegradation mechanisms. Further, the melting temperature and the melting point change of the various components in the PBAT/PLA blend before and after the biodegradation essentially followed the process of the changes in the respective single polymers. After biodegradation, the carbon atom content in the molecular structure of the PBAT, PLA, and PBAT/PLA samples decreased, while the oxygen atom content increased, indicating that the samples indeed degraded. The biodegradation rates of PBAT and PLA in the PBAT/PLA blend were not the same as those for the single materials.