The Effect of Acetylation on the Hydrolytic Degradation of PLA/Clay Nanocomposites

In this study, the hydrolytic degradation of Poly(lactic acid) (PLA) and acetylated PLA (PLA-Ac)–clay nanocomposites were investigated. The organo clay was obtained by ion exchange reaction using cetyl tri methyl ammonium bromide (CTAB). Nanocomposites containing 2, 5 and 8% mass ratio of organo clay (CTAB-O) were prepared. PLA and its organo clay nanocomposites were characterized by scanning electron microscope (SEM), thermo gravimetric analysis (TGA) and X-ray diffraction (XRD) to determine the morphology before and after hydrolytic degradation. Fourier transform infrared (FTIR) analyses of PLA and PLA-Ac were also obtained. The hydrolytic degradation of polymers and their composites were investigated in the phosphate buffered saline solution (PBS). The results showed that controlled hydrolytic degradation was observed in the samples with end group modification of PLA. While weight loss of PLA films was 28%, that of PLA-Ac films was 18% after 60 days degradation time. The weight loss was obtained as 29.5 and 25.5% for PLA-5 wt% organo clay (PLA/5CTAB-O) and PLA-Ac-5 wt% organo clay (PLA-Ac/5CTAB-O) nanocomposites films, respectively. It was also observed that thermal degradation of PLA-Ac was much more than that of PLA. Hydrolytic degradation increased depending on organo clay content. The end group modificated PLA results in controlled hydrolytic degradation. While hydrolytic degradation in polymer films occurred as surface erosion, bulk erosion was observed in composite films.     

Hydrolytic Degradation of PPDO/PDLLA Blends Containing the Compatibilizer PLADO

The poly(para-dioxanone) (PPDO)/poly poly (dl-lactide) (PDLLA) blends containing various contents of compatibilizer (0, 1, 3, 5, 10 %) were prepared by solution co-precipitation, which were dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) to form 10 % wt/vol solutions. Then in vitro hydrolytic degradation of PPDO/PDLLA blends containing poly (dl-lactide-co-para-dioxanone) (PLADO) as the compatibilizer was studied by the changes of weight loss, water absorption, thermal properties, surface morphology and mechanical properties of samples in phosphate buffered saline (pH 7.44) at 37 °C for 8 weeks. During the degradation, the weight loss and water absorption increased significantly for all blends, whereas hydrolysis rate of blends varied with the blend composition. The samples’ glass transition temperature decreased notably, while the degrees of crystallinity increased. Compared with uncompatibilized PPDO/PDLLA blends, PPDO/PDLLA blends with compatibilizer exhibited higher hydrolysis rate. The results suggested that the compatibilizer (PLADO) accelerated the hydrolysis rate of PPDO/PDLLA blends during the degradation.     

Degradation Kinetics of Biodegradable Fiber Composites

In a composite, fast degradable fibers determine the degradation of the slowly degradable matrix. Such biodegradable composites consisting of degummed hemp fibers and a polyester amide matrix were produced with fiber mass fractions between 0 and 0.48. The hot-pressed plates, 1-mm thick, were incubated in a standard soil. The degradation kinetics was quantified by the measurement of CO₂ production. Furthermore, after termination of experiment, the carbon balance was uncovered. The results were fitted to an exponential law taking into account the degradation of fibers. The increased amount of pores realized by high fiber contents induces pronounced degradation. The degradation is fully characterized by the time constant , which is correlated to the fiber mass fraction. The model allows to predict the degradation kinetics of composites with a few well-defined experiments.     

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.     

Influence of Short Central PEO Segment on Hydrolytic and Enzymatic Degradation of Triblock PCL Copolymers

Hydrolytic, enzymatic degradation and composting under controlled conditions of series of triblock PCL/PEO copolymers, PCEC, with central short PEO block (M _n 400 g/mol) are presented and compared with homopolymer (PCL). The PCEC copolymers, synthesized via ring-opening polymerization of ε-caprolactone, were characterized by ¹H NMR, quantitative ¹³C NMR, GPC, DSC and WAXS. The introduction of the PEO central segment (<?2 wt%) in PCL chains significantly affected thermal degradation and crystallization behavior, while the hydrophobicity was slightly reduced as confirmed by water absorption and moisture uptake experiments. Hydrolytic degradation studies in phosphate buffer after 8 weeks indicated a small weight loss, while FTIR analysis detected changes in crystallinity indexes and GPC measurements revealed bulk degradation. Enzymatic degradation tested by cell-free extracts containing Pseudomonas aeruginosa PAO1 confirmed high enzyme activity throughout the surface causing morphological changes detected by optical microscopy and AFM analysis. The changes in roughness of polymer films revealed surface erosion mechanism of enzymatic degradation. Copolymer with the highest content of PEO segment and the lowest molecular weight showed better degradation ability compared to PCL and other copolymers. Furthermore, composting of polymer films in a model compost system at 37 °C resulted in significant degradation of the all synthesized block copolymers.     

Morphological Study on Hydrolytic Degradation of Poly(tetramethylene succinate) Single Crystals and Spherulites

The morphological changes of Poly(tetramethylene succinate) single crystal lamellae by hydrolysis are investigated, using TEM, WAXD and SAXS. And the morphology of PTMS spherulites was also observed by optical microscopy after treatments as well as single crystal lamellae. The edge region of single crystal lamella can be most easily affected in the initial stage of hydrolysis. As the hydrolysis time increases, the lamellae are separated into small fragments which may be started from the uneven or irregular parts of the surface. The WAXD results showed that crystallinity were increased with increasing of treatment time. The lamellar thickness decreased at the initial stage of hydrolysis and increased again. There were cracks on the surface of spherulites after hydrolysis and the direction of cracks were tangential direction of spherulites. This result was thought to be from the uniformity of molecular arrangement in the crystallographic unit cell.     

二氧化钛光催化降解甲醛反应动力学研究

以钛酸丁酯为前驱体，应用溶胶一凝胶法制备TiO2粉体和负载TiO2薄膜，考察了不同活化温度和活化时间对TiO2光催化降解甲醛性能的影响，并对TiO2薄膜光催化降解甲醛的反应动力学进行了研究。试验结果表明，在活化温度450℃、活化时间5h条件下，所得TiO2粉体及薄膜的光催化活性较好。不同初始浓度下甲醛光催化降解率与时间关系的动力学研究表明，一级反应动力学模型与试验数据拟合较好，方差R^2大于或等于0．99。     

糙皮侧耳降解碱木素的动力学研究

对糙皮侧耳B1(白腐真菌的一种)降解碱木素的动力学进行了研究.基于Logistic方程,建立了糙皮侧耳B1在纯培养条件和碱木素存在条件下的生长动力学模型.动力学模型参数分别为0.94d-1和0.90d-1.该模型能够较好地模拟体系中生物量的变化,平均相对误差分别为3.2％和3.4％.糙皮侧耳B1对低浓度碱木素的降解存在...     

Degradation of Post-consumer PLA: Hydrolysis of Polymeric Matrix and Oligomers Stabilization in Aqueous Phase

Degradation of post-consumer PLA to lactic acid was analysed in order to assess the economic feasibility of the PLA chemical recycling process. Hydrolysis of PLA, in batch reactor, was analysed in the temperature range of 443–473 K, under autogenous pressure and a constant PLA to water ratio (equal to approximately 0.11 by weight), without the use of a catalyst. The experimental results suggest that the complete degradation of PLA can be obtained using relatively low reaction-times with the production of a mixture containing the monomer and traces of the dimer of lactic acid. The overall process was modelled using a two-step process: bulk degradation of PLA (in the solid or molten phase) with the solubilisation of low molecular weight oligomers, and their subsequent hydrolysis in water (stabilization). The model describes the trend of oligomer concentrations in the aqueous phase and PLA conversion as a function of time with both high accuracy and agreement with experimental results.     

电解法降解有机污染物机理及动力学的研究

对阳极电解催化降解有机污染物的机理进行了研究。结果表明 ,在电解过程中能够产生氧化能力极强的羟基自由基 (HO· ) ,使有机污染物以间接氧化的方式降解。用非线性最小二乘法对试验数据的分析表明 ,降解过程基本符合两步一级模型 ,并得到了水杨酸降解过程中的两步速率常数和 2 ,3-二羟基苯甲酸在 5 10 nm处的摩尔吸光系数     

Kinetics and Thermodynamics of Hydrolytic Depolymerization of Polyamide Waste at Various Temperature and Autogenious Pressure by High-Pressure Autoclave

Hydrolytic depolymerization of polyamide waste in water was studied using 0.5 L high pressure autoclave at temperatures of 235, 240, 245, 250 °C and at autogenious pressure 480, 500, 520, and 600 psi (pound per square inch).The reaction rate constant, energy of activation, enthalpy of activation, entropy of activation and equilibrium constant were calculated from the experimental data obtained. The maximum depolymerization (59.2%) of polyamide waste into monomer caprolactum was obtained at 250 °C and 600 psi pressure. The reaction rate constant was obtained on basis of measurement of amine value and residual weight. The depolymerization reaction was found to be pseudo first order with reaction rate constant of the order of 10⁻³ min⁻¹. The enthalpy, entropy and free energy of activation were recorded as 85.75, −0.1354 and 156.59 kJ mol⁻¹ respectively at the experimental conditions for maximum depolymerization of polyamide waste. The thermodynamic equilibrium constant for this hydrolysis reaction was found to be 2.3 × 10⁻¹⁶.     

Synthesis, Characterization, and Hydrolytic Degradation of Copolymers of 2-Methylene-1,3-dioxepane with Ethylene and with Styrene

2-Methylene-1,3-dioxepane (MDP) was copolymerized with ethylene (E) at a pressure of approximately 1000 psi and a temperature of approximately 70°C with AIBN as the free radical initiator. The copolymers obtained, poly(MDP-co-E), were characterized by elemental analysis, IR, ¹H-NMR and ¹³C-NMR spectroscopy, DSC, and GPC. The copolymers contained 2–15 mol% ester units. MDP was also copolymerized with styrene (S) at 120°C with di-t-butyl peroxide as the initiator to prepare the copolymer, poly(MDP-co-S). The number-average molecular weights of both types of copolymers were in the range of 6000 to 11,000, and the weight-average molecular weights were in the range of 9000 to 17,000. The melting temperatures of poly(MDP-co-E) decreased with increasing ester unit content in the copolymer. For the MDP-S copolymers, the glass transition temperatures decreased with increasing ester unit content. Both poly(MDP-co-E) and poly(MDP-co-S) were degraded by methanolysis, and their molecular weights decreased by the expected amounts based on the ester unit content.     

PLA and Organoclays Nanocomposites: Degradation Process and Evaluation of ecotoxicity Using Allium cepa as Test Organism

In this study, nanocomposites of PLA and organoclays Cloisite 20A and Cloisite 30B were prepared by the melt intercalation method and the obtained samples were characterized by transmission electron microscopy (TEM). Since composting is an important proposal to the final disposal of biopolymers, the influence of clays on the hydrolytic degradation process of PLA was evaluated by visual analysis and monitoring of molecular weight after periods of 15 and 30 days of degradation in compost. After degradation of the materials in composting environment, the evaluation of cytotoxic, genotoxic and mutagenic effects of compost aqueous extract was carried out using a bioassay with Allium cepa as test organism. The TEM micrographs permitted the observation of different levels of dispersion, including exfoliated regions. In the evaluation of hydrolytic degradation it was noted that the presence of organoclays can decrease the rate of degradation possibly due to the barrier effect of clay layers and/or the higher degree of crystallinity in the nanocomposite samples. Nevertheless, even in the case of nanocomposites, the molecular weight reduction was significant, indicating that the composting process is favorable to the chain scission of PLA in studied materials. In the analysis performed by the bioassay using A. cepa as test organism, it was found that after degradation of the PLA and its nanocomposites the aqueous extract of compost samples induced a decreasing in the mitotic index and an increasing in the induction of chromosomal abnormalities. These results were statistically significant in relation to the negative control (distilled water). By comparing the results obtained for the nanocomposites in relative to pure polymer, there were no statistically significant differences. The types of the observed chromosomal aberrations indicated a possible genotoxic effect of the materials, which may be related to an aneugenic action of PLA degradation products.     

Degradation of Polylactic Acid (PLA) Plastic in Costa Rican Soil and Iowa State University Compost Rows

In this study the degradation of polylactic acid (PLA) plastic films in Costa Rican soil and in a leaf composting environment was investigated. Three types of PLA films were used: Ch-I, (PLA monolayer plastic films from Chronopol, Golden, CO), GII (PLA trilayer plastic films from Cargill Dow Polymers LLC, Minnetonka, MN), and Ca-I (PLA monolayer plastic films from Cargill Dow Polymers LLC). The average soil temperature and moisture content in Costa Rica were 27°C and 80%, respectively. The average degradation rate of PLA plastic films in the soil of the banana field was 7675 M _w/week. Two compost rows were set up at the Iowa State University (ISU) (Ames) compost site. Temperature and relative humidity of the compost rows were kept at 55 ± 5°C and 50 ± 10% RH, respectively. The degradation rates of GII and Ca-I in the compost rows were 113,290 and 71,283 M _w/week, respectively. Therefore, it was estimated that in Costa Rican soil and in compost rows, PLA would be visibly degraded in 6 months and in 3 weeks, respectively.     

不同光照度下活性艳红X-3B的光催化降解动力学研究

以活性艳红X-3B为模型化合物，以TiO2为光催化剂，研究了不同光照度下污染物的多相光催化降解动力学。结果表明，活性艳红X-3B的光催化降解动力学符合Langmiur—Hinshelwood动力学模型，其中的表观反应速率常数(k)随入射光照度的增加而增大，吸附平衡常数(KA)却随入射光照度的增加而减小，在实验的光照度范围内，k和KA^-1与光照度的平方根成比。     

Degradation of Cellulosic Materials Under the Alkaline Conditions of a Cementitious Repository for Low- and Intermediate-Level Radioactive Waste. II. Degradation Kinetics

The degradation of cellulosic materials, differing mainly in the degree of polymerization and the number of reducing end groups, was studied under the alkaline conditions similar to those existing in a cementitious repository for low- and intermediate-level radioactive waste (pH 13.3, T = 25°C). The kinetics of alkaline degradation (peeling-off reaction) were studied and the data analyzed by the model of Haas et al. [13]. The observed kinetic parameters for the propagation reaction and overall stopping reaction were compared with literature data. Although measured under different experimental conditions, literature data and data from this study show a consistent picture. Differences in the extent of degradation observed for the different cellulosic materials could be satisfactorily explained by differences in reducing end group content and, consequently, by differences in the degrees of polymerization. Besides the number of reducing end groups, the degree of amorphousness also plays an important role. The main degradation products formed under the experimental conditions used are - and -(gluco)isosaccharinic acid. This is in agreement with many other studies on alkaline degradation of cellulose. The two isomers are formed in roughly equal amounts.     

Thermal Degradation and Kinetics of Alginate Polyurethane Hybrid Material Prepared from Alginic Acid as a Polyol

Alginate polyurethane hybrid materials are prepared by varying mole ratio of 2, 4-TDI as a di-isocyanate and alginic acid as a polyol in presence of dimethyl sulfoxide (DMSO) as a solvent. FT-IR and ¹³C one-dimensional (1D) solid state NMR (SSNMR) spectroscopy indicates that alginic acid is converted into alginate-polyurethane hybrid material via urethane linkage. Surface morphology of alginate-polyurethane hybrids changes by varying alginic acid: TDI ratio. The peak at near 221 °C in DSC thermogram of alginic acid (Alg) is shifted to higher temperature in alginate-polyurethane hybrid (Algpu1 and Algpu2). TGA study shows that alginate-polyurethane hybrid prepared using alginic acid: TDI = 1:1 (Algpu2) is more stable than alginic acid: TDI = 1:0.5 (Algpu1) at 300 °C. Kinetic analysis was performed to fit with TGA data, where the entire degradation process has been considered as three consecutive 1st order reactions. This study shows that thermal stability of alginate-polyurethane hybrid material was increased by adjusting mole ratio of 2, 4-TDI and alginic acid.     

PLA Chemical Recycling Process Optimization: PLA Solubilization in Organic Solvents

The recycling of used, post-industrial and post-consumer PLA is crucial to reduce both the consumption of renewable resources for the monomer synthesis and the environmental impact related to its production and disposal. Several processes are actually available: among these, there is a particular interest on the chemical recycling of PLA with production of its monomer. The aim of this work is to analyse the PLA dissolution behaviour in different organic solvents (acetone and Ethyl lactate) at different water concentrations in order to optimize the chemical depolymerisation process of PLA. New experimental data are presented and a kinetic model is provided for a first analysis. Preliminary results suggest that acetone based solvents (i.e., acetone water mixtures at various concentrations) are more effective to solubilize the PLA rather than the Ethyl-lactate based solvent. Anyway, an increase of water concentration in the solvent phase, determines both a reduction of the solvent power and a reduction of mass transport coefficient for the two solvents tested.     

Water transport in polylactic acid (PLA), PLA/ polycaprolactone copolymers, and PLA/polyethylene glycol blends

Polylactic acid (PLA) is a hydrolytically degradable aliphatic polyester, and water vapor permeability may have a significant influence on the rate of degradation. A method is devised to use bags prepared from PLA films and filled with molecular sieves to determine the water vapor permeability in the polymer, its copolymers with caprolactone, and blends with polyethylene glycol. The “solution-diffusion” model is used to determine the permeability parameters. These include the solubility coefficient,S, a measure of the equilibrium water concentration available for hydrolysis and the diffusion coefficient,D, which characterizes the rate of water vapor diffusion into the film under specific conditions. Values ofS andD at 50‡C and 90% relative humidity ranged from 400 × 10^-6 to 1000 × 10^-6 cm³ (STP)/(cm³ Pa) and 0.20 × 10^-6 to 1.0 × 10^-6 cm²/s, respectively. TheS andD coefficients were also measured at 20 and 40‡C and compared to those of other polymers. The degree of crystallinity was found to have little influence on the measured permeability parameters. The heat of sorption, δH_S, and the activation energy of diffusion, E_D, were used to show that the permeability process is best described by the “water cluster” model for hydrophobic polymers. Finally, the diffusion coefficient is used to compare the rate of water diffusion to the rate of water consumption by ester hydrolysis. Results indicate that hydrolytic degradation of PLA is reaction-controlled.