Physical Properties and Fiber Morphology of Poly(lactic acid) Obtained from Continuous Two-Step Melt Spinning

Fibers of poly(lactic acid) (PLA) produced by two-step melt-spinning are studied. The PLA resin used contains a 98:02 ratio of l:d stereochemical centers. A range of processing conditions is explored. The cold-draw ratio is varied from 1 to 8 under conditions of constant heating. In addition, three draw ratios are studied at three different heating rates. The thermal, mechanical, and morphological properties of the resultant fibers are determined. Properties can be widely manipulated through a combination of draw ratio and draw temperature. A maximum tensile strength and modulus of 0.38 GPa and 3.2 GPa, respectively, are obtainable. Using atomic force microscopy, the fiber morphology is found to be highly fibrillar; microfibril diameters are roughly 40 nm in diameter. Very high draw ratios cause the fiber to turn from shiny and translucent to dull and white; this transition is attributed to surface crazing. Significant molecular weight loss is observed upon processing (weight-average molecular weights drops between 27% and 43%).     

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.     

链霉菌(Streptomyces sp.)对吡啶的降解特性

从焦化废水的活性污泥中分离出对溶液中吡啶具有降解效果的链霉菌（Streptomyces sp．）,考察了吡啶初始质量浓度、初始pH、降解温度、振荡速度等对吡啶降解效果的影响,初步探讨了该菌降解吡啶的动力学与机理。实验结果表明,该菌对吡啶有很强的耐受力,能以吡啶为惟一碳源和氮源生长。链霉菌在初始pH=8、降解温度30℃、振荡速度100r／min的条件下培养7d后,吡啶的质量浓度从250mg/L降至6．6mg/L,吡啶降解率达97．4％。该菌对吡啶的降解反应符合一级动力学方程,初始质量浓度为100mg／L时的吡啶降解速率常数为0．4011d^-1。紫外一可见光谱分析表明,吡啶经该菌降解后的特征环被破坏。     

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

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

The basic properties of poly(lactic acid) produced by the direct condensation polymerization of lactic acid

Poly(lactic acids) with high molecular weights have been synthesized by direct condensation polymerization of lactic acid. These polymers have good mechanical properties and can be processed into products such as cups, film, and fiber, which can be used as compostable materials. This polymerization method can be applied to the synthesis of copolymers of lactic acid and other hydroxyacids. The properties of poly(lactic acid) and copolymers synthesized by the direct process are different from those of polymers obtained by the conventional lactide process.     

镰刀菌HJ01对对氯苯酚的降解特性

采用实验室分离的一株镰刀菌HJ01,以对氯苯酚(4-CP)为降解底物,以蔗糖为外加碳源,考察了蔗糖质量浓度、降解温度、初始pH对4-CP降解效果的影响,初步探讨了镰刀菌HJ01对4-CP的降解动力学和降解机理.实验结果表明:该菌株能以4-CP为惟一碳源和能源生长;在外加蔗糖为碳源,蔗糖质量浓度为3 g/L、降解温度为30℃、初始pH为8的条件下,50 mg/L4-CP能在6 d内被完全降解.以4-CP为惟一碳源和外加蔗糖下的降解动力学分别符合Haldane模型和一级动力学方程.     

Degradation of Commercial Biodegradable Packages under Real Composting and Ambient Exposure Conditions

The use of long-lasting polymers as packaging materials for short lived applications is not entirely justified. Plastic packaging materials are often soiled due to foodstuffs and other biological substances, making physical recycling of these materials impractical and normally unwanted. Hence, there is an increasing demand for biodegradable packaging materials which could be easily renewable. Use of biopolymer based packaging materials allows consideration of eliminating issues such as landfilling, sorting and reprocessing through taking advantage of their unique functionality, that is compostability. Composting allows disposal of biodegradable packages and is not as energy intensive compared to sorting and reprocessing for recycling, although it requires more energy than landfilling. The aim of this work was to study the degradation of three commercially available biodegradable packages made of poly (ld-lactide) (PLA) under real compost conditions and under ambient exposure by visual inspection, gel permeation chromatography, differential scanning calorimetry, and thermal gravimetric analysis. A novel technique to study the degradability of these packages and to track the degradation rate under real compost conditions was used. The packages were subjected to composting for 30 days, and the degradation of the physical properties was measured at 1, 2, 4, 6, 9, 15 and 30 days. PLA packages made of 96% l-lactide exhibited lower degradation than PLA packages made of 94% l-lactide, mainly due to their highly ordered structure, therefore, higher crystallinity. The degradation rate changed as the initial crystallinity and the l-lactide content of the packages varied. Temperature, relative humidity, and pH of the compost pile played an important role in the total degradation of the packages. A first order degradation of the molecular weight as a function of time was observed for the three packages.     

镰刀菌HJ01对苯酚的降解性能

为了研究真菌对苯酚的降解能力,采用本实验室分离的一株镰刀菌HJ01,考察了外加碳源、降解体系初始pH、温度对HJ01菌体生长量和苯酚降解效果的影响,初步探讨了镰刀菌降解苯酚的动力学与机理。实验结果表明,该菌能以苯酚为惟一碳源生长,添加适量的蔗糖可促进HJ01菌体的生长及苯酚的降解。在蔗糖加入量为3g／L、降解体系初始pH为6．0、温度为30℃的最佳条件下,经HJ01菌处理4d后的质量浓度为420mg／L苯酚废水中的苯酚完全降解。镰刀菌的生长和苯酚降解动力学符合Andrews模型。     

几种金属氧化物催化臭氧氧化降解p-CBA

选择Al₂O₃,TiO₂,MnO₂,Fe₃O₄ 4种金属氧化物对溶液中的对氯苯甲酸（p-CBA）进行催化臭氧氧化降解。催化剂的表征结果显示：TiO₂具有最大的比表面积,为93.84 m²/g,Al₂O₃的比表面积最低,仅为10.28 m²/g;MnO₂和Fe₃O₄表面含有大量强酸性位,故其等电点较低,分别为1.45和1.82。4种催化剂对p-CBA的吸附能力与其比表面积相关,而催化臭氧氧化活性高低却与其等电点的高低顺序一致。Al₂O₃具有最高的等电点（6.92）,也表现出相对较强的催化臭氧氧化活性。在臭氧通量6 mg/min、p-CBA初始质量浓度40 mg/L、Al₂O₃投加量0.5 g/L、反应时间40 min的条件下,p-CBA去除率达到58.6%,远高于单独臭氧化和吸附过程的去除率。     

4株正十六烷降解菌的降解能力及代谢动力学特性

从处理采油废水的活性污泥中分离出4株产生物表面活性剂的正十六烷高效降解菌。菌株A14和B45为非脱羧勒克菌（Leclercia adecarboxylata）,菌株C28和A27为肠杆菌（Enterobacter sp.）。在NaCl质量浓度15~25 g/L、pH 6.0~7.0、接种量10%（φ）,培养温度37 ℃,摇床转速160 r/min、正十六烷体积分数0.30%的条件下降解16 d后,菌株A14、B45、C28和A27的正十六烷降解率分别为93.7%,87.8%,73.3%,65.7%。4株菌所产生的生物表面活性剂均为磷脂类表面活性剂。菌体生长满足逻辑斯蒂模型,正十六烷的降解满足一级反应动力学模型。菌株C28、A27的生长速率快于菌株A14、B45,菌株A14、B45的正十六烷降解速率快于菌株C28、A27。     

The Effect of Masterbatch Addition on the Mechanical, Thermal, Optical and Surface Properties of Poly(lactic acid)

There has been considerable interest in the use of the biodegradable polymer poly(lactic acid) (PLA) as a replacement for petroleum derived polymers due to ease of processability and its high mechanical strength. Other material properties have however limited its wider application. These include its brittle properties, low impact strength and yellow tint. In an attempt to overcome these drawbacks, PLA was blended with four commercially available additives, commonly known as masterbatches. The effect of the addition of 1.5 wt% of the four masterbatches on the mechanical, thermal, optical and surface properties of the polymer was evaluated. All four masterbatches had a slight negative effect on the tensile strength of PLA (3–5% reduction). There was a four fold increase in impact resistance however with the addition of one of the masterbatches. Differential scanning calorimetry demonstrated that this increase corresponded to a decrease in the polymer crystallinity. However there was an associated increase in polymer haze with the addition of this masterbatch. The clarity of PLA was improved through the addition of an optical brightener masterbatch, but the impact resistance remained low. The glass transition and melting temperatures of PLA were not affected by the addition of the masterbatches, and no change was observed in surface energy. Some delay in PLA degradation, in a PBS degradation medium at 50 °C, was observed due to blending with these masterbatches.     

The Effect of Nanoclays on the Properties of PLLA-modified Polymers Part 1: Mechanical and Thermal Properties

Organically modified montmorillonite clays were incorporated at a 5% loading level into film grade of poly-L-lactic acid (PLLA) using a variety of masterbatches based on either semi-crystalline or amorphous poly-(lactic acid), as well as biodegradable aromatic aliphatic polyester. The PLLA masterbatches and compounded formulations were prepared using a twin screw compounding extruder, while the films were prepared using a single screw cast film extruder. The thermal and mechanical properties of the films were examined in order to determine the effect of the clay and different carriers on the polymer–clay interactions. In the optimal case, when a PLLA-based masterbatch was used, the tensile modulus increased by 30%, elongation increased by 40%, and the cold crystallization temperature decreased by 15 °C, compared to neat PLLA. The properties improvement of PLLA films containing nano clays demonstrated the possibility to extend the range of biodegradable film applications, especially in the field of packaging.     

电生成Fenton试剂处理染料废水

对电生成Fenton试剂处理酸性铬兰K染料废水进行了研究。采用石墨作阴、阳极,电解过程中向阴极表面通纯氧,并在废水中加入-定量的Fe2+,氧在阴极上还原生成H2O2,H2O2又产生强氧化剂·OH,进而对酸性铬兰K染料废水进行脱色降解。在槽电压为6 V、pH为2.5、电解液中FeSO4·7H2O的质量浓度为0.5 g／dm3、Na2SO4的质量浓度为20 g／dm3的条件下电解废水60 min,染料废水脱色率和COD去除率分别达74.1％和57.9％,电解废水120min后,染料废水脱色率和COD去除率分别达92.9％、71.3％。动力学研究表明,染料的降解符合一级动力学过程,速率常数k为0.02224 min-1。     

Alkaline Degradation of Cellulose: Mechanisms and Kinetics

Cellulose powder and softwood sawdust were subjected to alkaline degradation under conditions representative of a cementitious environment for periods of 7 and 3 years, respectively. During the first 3 years, sampling was frequent, and data on the degradation of cellulose and production of isosaccharinic acid was used for establishing long-term prediction models. Samples after an additional period of 4 years were compared to the predicted values. The total rate of degradation was measured as the increase in total organic carbon (TOC) in corresponding solutions. A previously published theoretical model of degradation kinetics gave a good approximation of the present experimental data. Peeling-off, stopping, and alkaline hydrolysis reaction rate constants were obtained as model parameters, and the results suggested that the transformation of the glucose end group is the rate-limiting step in the cellulose peeling-off reaction and also determines the pH dependence of that reaction. After 3 years, isosaccharinic (ISA) acid represented 70–85% of all degradation products as quantified by capillary zone electrophoresis. The long-term prediction model indicated that all of the cellulose would be degraded after only 150–550 years. The control sampling after 7 years points toward a lower degradation of cellulose and production of ISA than predicted by the model, reflecting either a degradation of ISA that was faster than the production or a termination of the ISA production.     

Degradation of poly(3-hydroxybutyrate), PHB,by bacteria and purification of a novel PHB depolymerase fromComamonas sp.

Bacteria capable of growing on poly(3-hydroxybutyrate), PHB, as the sole source of carbon and energy were isolated from various soils, lake water, activated sludge, and air. Although all bacteria utilized a wide variety of monomeric substrates for growth, most of the strains were restricted to degrade PHB and copolymers of 3-hydroxybutyrate and 3-hydroxyvalerate, P(3HB-co-3HV). Five strains were also able to decompose a homopolymer of 3-hydroxyvalerate, PHV. Poly(3-hydroxyoctanoate), PHO, was not degraded by any of the isolates. One strain, which was identified asComamonas sp., was selected, and the extracellular depolymerase of this strain was purified from the medium by ammonium sulfate precipitation and by chromatography on DEAE-Sephacel and Butyl-Sepharose 4B. The purified PHB depolymerase was not a glycoprotein. The relative molecular masses of the native enzyme and of the subunits were 45,000 or 44,000, respectively. The purified enzyme hydrolyzed PHB, P(3HB-co-3HV), and—at a very low rate—also PHV. Polyhydroxyalkanoates, PHA, with six or more carbon atoms per monomer or characteristic substrates for lipases were not hydrolyzed. In contrast to the PHB depolymerases ofPseudomonas lemoignei andAlcaligenes faecalis T₁, which are sensitive toward phenylmethylsulfonyl fluoride (PMSF) and which hydrolyze PHB mainly to the dimeric and trimeric esters of 3-hydroxybutyrate, the depolymerase ofComamonas sp. was insensitive toward PMSF and hydrolyzed PHB to monomeric 3-hydroxybutyrate indicating a different mechanism of PHB hydrolysis. Furthermore, the pH optimum of the reaction catalyzed by the depolymerase ofComamonas sp. was in the alkaline range at 9.4.     

Degradation of Poly(acrylic acid)s with Phenolic Side-Chains by Manganese Peroxidase from White Rot Fungi

Poly(acrylic acid)s (PAAs) with various functional groups, such as phenolic hydroxyl, amino, and aldehyde groups, in the side-chains were treated with manganese peroxidase (MnP) prepared from the culture of lignin-degrading white rot fungi. While no change in the M_w of PAA without a functional group was observed after a 24-h MnP treatment, the M_w␣of␣PAA␣with p-aminophenol as side-chains decreased from 90,000 to 59,000, and that with␣o-aminophenol from 70,000 to 26,000. MnP treatment also decreased the M_w of PAA with a p-aminoaniline or aldehyde group. Furthermore, the MnP treatment generated a significant depolymerization of the cross-linked PAA with p-aminophenol from an insoluble polymer to water soluble products. These results suggest that functional groups generating radicals can act as elemental devices and induce degradation of the PAA main chain.     

Degradation of L- and DL-lactic acid oligomers in the presence ofFusarium moniliforme andPseudomonas putida

Poly(-alkanoates) derived from lactic acid enantiomers are known to degrade easily hydrolytically in aqueous media. The ability of two microorganisms, a filamentous fungus,Fusarium moniliforme, and a bacterium,Pseudomonas putida, to assimilate the degradation by-products of poly(lactic acid) (PLA), namely, lactic acid, lactyllactic acid dimers, and higher oligomers, was investigated in liquid culture. To distinguish the influence of chirality on bioassimilation, two series of substrates were considered which derived from the racemic and the L-form of lactic acid, respectively. The fate of these compounds was monitored by HPLC. Under the selected conditions,DL- andL-lactic acids were totally used by the two microorganisms regardless of the enantiomeric composition. Both microorganisms degraded the LL-dimer rather rapidly. However,F. moniliforme acted more rapidly thanP. putida. It is likely that the DD-dimer also biodegraded but at a slower rate, especially in the case of the fungi. Higher racemic oligomers were slowly assimilated by the two microorganisms, whereas higher L-oligomers appeared biostable probably because of their crystallinity. A synergistic effect was observed when both microorganisms were present in the same culture medium containing racemic oligomers.Presented at the 4th International Workshop on Biodegradable Plastics and Polymers, October 11–14, 1995. Durham, New Hampshire.     

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.     

The biodegradation of lactic acid-based poly(ester-urethanes)

The biodegradability of lactic acid based poly(ester-urethanes) was studied using the headspace test method, which was performed at several elevated temperatures. The poly(ester-urethanes) were prepared using a straight two-step lactic acid polymerization process. The lactic acid is first condensation polymerized to a low molecular weight hydroxyl-terminated telechelic prepolymer and then the molecular weight is increased with a chain extender such as diisocyanate. In the biodegradation studies the effect of different stereostructures (different amounts of D-units in the polymer chain), the length of ester units, and the effect of crosslinking on the biodegradation rate were studied. The results indicate that poly(ester-urethanes) do not biodegrade at 25‡C, but at elevated temperatures they biodegrade well. The different stereostructures and crosslinking have a strong influence on the biodegradation rate. The length of ester units in the polymer chain also affects the biodegradation rate, but much less than crosslinking and stereostructure.     

Abiotic Hydrolysis of Some Poly-D-glucaramides and Subsequent Microbial Utilization/Degradation

Carbohydrate acid amides, diamides and polyamides have been proposed to be utilized as nitrogen plant fertilizers or fertilizer components, and experiments with Brassica rapa demonstrated a positive biological response when these compounds were used as the only source of fixed nitrogen for plant growth. The present study was carried out with the aim of elucidating the mechanism of degradation of these polymers in both soil/compost and in liquid media and the role of microorganisms in this process. The results obtained suggest that a major route of degradation of polyglucaramides in the environment is their abiotic hydrolysis/release of the diacid and diamine building block units of these polymers, which are then utilized for growth by microorganisms. In cell-free crude extracts from enrichment cultures obtained with different poly-D-glucaramides, no enzyme activities catalyzing the release of diamines from these compounds were detected.