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.     

Biosynthesis and Characterization of Laccase Catalyzed Poly(Catechol)

Enzymatic polymerization of catechol was conducted batch-wise using laccase enzyme produced by the culture Trametes versicolor (ATCC 200801). The polymerization reaction was carried out in 1:1 (v/v) aqueous-acetone solution, buffered at pH 5.0 with sodium acetate (50 mM) in a sealed, temperature-controlled reactor at 25°C. The molecular weight of the produced polymer was determined with GPC. FT-IR, DSC, and TGA were employed to investigate the structure and thermal behavior of synthesized poly(catechol). It was found that catechol units were linked together with ether bonds and thermal stability of the catechol increased in the poly(catechol) polymeric structure effectively. The number average molecular weight of poly(catechol) was found as 813 ± 3 Da with a very narrow polydispersity value of 1.17 showing selective polymerization of catechol by the enzyme.     

Effects of Diisocyanate and Polymeric Epoxidized Chain Extenders on the Properties of Recycled Poly(Lactic Acid)

Increasing demand in the use of poly(lactic acid) (PLA) leads to a debate about using potential foodstuffs for plastic production and a moral issue when starvation problem is taken into account. One of the solutions is recycling of PLA; however, recycling results in property losses during melt processing due to low thermal stability of PLA. This study focuses on using chain extenders to offset thermal degradation of recycled PLA. The effects of a diisocyanate and a polymeric epoxidized chain extender on the properties of the recycled poly(lactic acid) were investigated. In order to mimic the recycling process, PLA was subjected to thermo-mechanical degradation using a laboratory scale compounder. Chain extender type, loading and mixing time were investigated. On-line rheology and intrinsic viscosity measurements of PLA before and after chain extension confirmed that the molecular weight increased. Dynamic mechanical analysis, rheology and tensile tests revealed that the chain extenders led to a significant increase in modulus, strength and melt-viscosity. It was found that diisocyanate had slightly higher and faster chain extension reactivity than polymeric extender. Differential scanning calorimetry results showed an increase in the crystallization temperature due to the branched and extended chain structure.     

Comparative Investigations on Optimum Polymerization Conditions for the Synthesis of a Sustainable Poly(Lactic Acid)

The development of synthetic biodegradable polymers using solvent free polymerization has a unique potential to be used as sustainable polymers in biomedical applications. The aim of this work was to synthesize and characterize a sustainable class of poly(lactic acid) (PLA) under different operating conditions via direct polycondensation of lactic acid (LA). Several parameters were tested including the absence of solvents and catalysts on the polymerization, in addition to polymerization temperature and time. Polymerization conditions were evaluated using response surface method (RSM) to optimize the impact of temperature, time, and catalyst. Results showed that molecular weight (M_w) of PLA increased with increasing polymerization time. Highest M_w of 28.4 kD with relatively a broad polydispersity 1.9 was achieved at polymerization temperature 170?°C at 24 h in the free solvent polymerization. This led to a relevant inherent viscosity of 0.37 dl/g. FTIR spectra exhibited a disappearance of the characteristic peak of the hydroxyl group in LA at 3482 cm^?1 by increasing the intensity of carbonyl group. The ¹H nuclear magnetic resonance (NMR) exhibited the main chain at 5.22 ppm and the signal of methyl proton at 1.61 ppm as well as a signal at 4.33 and 1.5 assigned to the methane proton next to the terminal hydroxyl group and carboxyl group respectively. Meanwhile, the PLA synthesized with a catalyst [Sn(Oct)₂] in a free solvent demonstrated comparatively high thermal transition properties of glass transition, melting, and crystallinity temperatures of 48, 106, and 158?°C, respectively. These results are of significant interest to further expand the use of PLA in biomedical applications.     

Preparation of Soybean Oil Polymers with High Molecular Weight

The cationic polymerization of soybean oils was initiated by boron trifluoride diethyl etherate in supercritical carbon dioxide medium. The resulting polymers had molecular weight ranging from 21,842 to 118,300 g/mol. Nuclear magnetic resonance spectroscopy and gel permeation chromatography analysis confirmed the polymerization had occurred. Parameters affecting the polymerization were studied, which included initiator amount and reaction time. Results show that the longer reaction time, up to 3 h, favored the higher molecular weight of polymers at conditions of 140 °C and initiator BF₃·OEt₂ (2.5 g, 0.018 mol). When reaction time was increased further, the molecular weight of polymers stayed the same or slightly decreased. Increased concentration of initiator gave the higher molecular weight of polymers. The high molecular weight polymers were possibly formed through two path ways: polymerization and intermolecular Diels-Alder reaction.     

N-长链碳酰基-L-苯丙氨酸单甲基聚乙二醇酯的合成及其性质研究

以L-苯丙氨酸、长链烷基（C₁₂/C₁₄/C₁₆/C₁₈）酰氯和聚乙二醇单甲醚（MPEG,M_n=350,550,750,1 000 g/mol）为原料,合成了一系列新型非离子型表面活性剂N-长链碳酰基-L-苯丙氨酸单甲基聚乙二醇酯（Rn-L-MPEG）,系统研究了表面张力、界面张力和土壤吸附性与其结构之间的关系。结果表明：随着MPEG分子量的增大,Rn-L-MPEG的表面张力逐渐下降;随着酰氯中烷基链的增长,Rn-L-MPEG的表面张力呈现增大趋势,系列表面活性剂中R12-L-MPEG1000具有最低的表面张力28.11 mN/m;Rn-L-MPEG的界面张力随分子结构变化的规律同表面张力;随着MPEG分子量的增大,Rn-L-MPEG的饱和吸附量逐渐增大,随着酰氯中烷基链的增长,Rn-L-MPEG的饱和吸附量呈现下降趋势。     

Biodegradable Poly(lactic acid) Blends with Chemically Modified Polyhydroxyoctanoate Through Chain Extension

Poly(lactic acid) (PLA) was blended with chemically modified Polyhydroxyoctanoate (mPHO) using a Haake twin-screw mixer. Due to the melt viscosity disparity between the two components, PHO was reacted with Hexamethylene diisocyanate (HDI) used as a chain extender to produce high molecular weight for improving compatibility and processability with PLA. The number average and weight average molecular weight of the PHO, reacted with 0.55 wt% HDI, were increased 314 and 275%, respectively, compared with those of the unmodified PHO. The blends were characterized for rheological, thermal, and mechanical properties. Infrared spectra confirmed the formation of the urethane linkages in mPHO. The shear viscosity, as a function of shear rate or shear stress, decreased with an increase in mPHO content, indicating that the PLA/mPHO blends show shear-thinning behavior along with the power-law model. DSC thermograms showed that the two components in the blends were found with two crystalline phases and two amorphous phases confirming the coexistence of two immiscible components. Tensile results indicated that tensile strength for blends decreased with increasing mPHO content up to 80%. A decrease in elastic modulus, as well as an increase in elongation at break, was seen as a function of mPHO content. Results of aging tests showed that the mechanical properties of the blends also dropped more at a higher PLA level when compared with those of the unaged samples.     

Diethanolamides of Castor Oil as Polyols for the Development of Water-Blown Polyurethane Foam

Castor oil was chemically modified into a diethanolamide by a two step process. The first step was the hydroxylation of double bonds in castor oil and second step was the transamidation using diethanolamine to increase the hydroxyl value. Water blown polyurethane foams were developed with this castor oil based polyol using polypropylene glycol of molecular weight 1,000 as the copolyol and polymeric MDI. The density and mechanical properties namely compression and flexural strength depended on the composition of the foam formulation. The hydroxyamide content and molecular weight of commercial polyol had significant effect on the micro structure as observed by optical microscopy.     

Palm Oleic Acid Based Alkyds: Effect of the Fatty Acid Content on the Polyesterification Kinetics

The kinetic behavior of polyesterification of the alkyd resins synthesized using glycerol and phthalic anhydride modified with oleic acid from the palm oil at temperatures between 120 and 240 °C was studied. Three alkyds having oleic acid contents of 28, 40, and 65% were prepared by employing fatty acid method. The extent of the polyesterification reaction and average degree of polymerization were monitored by determining the acid number of the aliquot of the reaction mixture at various intervals of time and by measuring the volume of water evolved. Kinetic studies revealed that initial reaction rates followed a second-order kinetics up to certain limit and thereafter deviations were observed. The extent of reaction varied from 77.4 to 86.3% before deviation for all the three samples and exhibited a considerable degree of conversion. The second-order rate constants calculated from the linear part were found to be of the order of 10⁻⁵ g (mg KOH)⁻¹ min⁻¹. Molecular weight of the alkyd samples was determined by GPC; number average molecular weight of the alkyds ranged from 980 to 2,070.     

Melt Strength and Rheological Properties of Biodegradable Poly(Lactic Aacid) Modified via Alkyl Radical-Based Reactive Extrusion Processes

Poly(lactic acid) (PLA) has been modified using twin-screw reactive extrusion to improve its melt properties and crystallinity. In this work lauroyl peroxide was used as an alkyl free radical source, abstracting hydrogen atoms from the PLA backbone leading to branching and chain extension reactions. Once the linear viscoelastic region was determined for these polymers, changes in dynamic rheology (dynamic viscosity real and loss modulus) were measured. Gel permeation chromatography showed that the molecular weight and polydispersity increased to a maximum with the addition of 1.00 and 0.50?wt% peroxide, respectively. Low temperature ?? transitions in dynamical mechanical thermal traces gave further evidence that branching had also occurred. G?ttfert Rheotens measurements showed a three fold increase in melt strength due to both increased chain length and branching. Thermal analysis showed the level of crystallisation had decreased also possibly due to branching. Reductions in crystallinity and improved melt strength are known to be critical for film and foam formation.     

A Novel Biodegradable Green Poly(l-Aspartic Acid-Citric Acid) Copolymer for Antimicrobial Applications

Poly (l-aspartic acid-citric acid) green copolymers were developed using thermal polymerization of aspartic acid (ASP) and citric acid (CA) followed by direct bulk melt condensation technique. Antibacterial properties of copolymer of aspartic acid based were investigated as a function of citric acid content. This study is focused on the microorganism inhibition performance of aspartic acid based copolymers. Results showed that inhibition properties increase with increasing citric acid content. Characterization of obtained copolymers was carried out with the help of infrared absorption spectra (FTIR), x-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermo gravimetric analysis (TGA). The antibacterial activity of copolymers against bacteria like E-coli, Bacillus and pseudomonas was investigated. The copolymers showed excellent antimicrobial activities against three types of microorganisms. Overall studies indicated that the above copolymers possess a broad wound dressing activity against above three types of bacteria and may be useful as antibacterial agents.     

Study on Properties of Poly(urethane-ester) Synthesized from Prepolymers of ε-Caprolactone and 2,2-Dimethyl-1,3-Propanediol Monomers and Their Biodegradability

Poly(urethane-ester) was prepared by polymerization of 4,4′-methylenebis(phenyl isocyanate) (MDI) and prepolymers of ε-caprolactone and 2,2-dimethyl-1,3-propanediol monomers P(CL-DP) with various chain lengths as polyol sources. Characterizations of poly(urethane-ester) were carried out by analysis of functional groups (FTIR), thermal properties (DTA/TGA), mechanical properties (Tensile tester), crystallinity (XRD), and biodegradability. The chain length of prepolymers used in polymerization has a significant effect in properties of poly(urethane-ester) as well as their biodegradability. The formation of poly(urethane-ester) was indicated by the presence of new absorption peaks at wave number of 3,348.2 and 1,596.9 cm^?1 for urethane (–NH–) and aromatic groups in chain of polymers, respectively. The increase chain length of prepolymer used in polymerization with 4,4′-methylenebis(phenyl isocyanate) was observed the increase thermal property and crystallinity of poly(urethane-ester). However, the maximum mechanical property and also biodegradability in activated sludge were observed in poly(urethane-ester) prepared by polymerization of 4,4′-methylenebis(phenyl isocyanate) (MDI) and P(CL-DP) prepolymers with DP/CL ratio of 1/20. Apparently, the amorphous parts of polymers are rapidly decomposed by enzymes of microorganisms, so the crystallinity on the whole of poly(urethane-ester) increases after incubation time of 30 days.     

The Properties of Poly(<Emphasis Type="SmallCaps">l</Emphasis>-Lactide) Prepared by Different Synthesis Procedure

Different synthesis methods were applied to determine optimal conditions for polymerization of (3S)-cis-3,6-dimethyl-1,4-dioxane-2,5-dione (l-lactide), in order to obtain poly(l-lactide) (PLLA). Bulk polymerizations (in vacuum sealed vessel, high pressure reactor and in microwave field) were performed with tin(II) 2-ethylhexanoate as the initiator. Synthesis in the vacuum sealed vessel was carried out at the temperature of 150 °C. To reduce the reaction time second polymerization process was carried out in the high pressure reactor at 100 °C and at the pressure of 138 kPa. The third type of rapid synthesis was done in the microwave reactor at 100 °C, using frequency of 2.45 GHz and power of 150 W at the temperature of 100 °C. The temperature in this method was controlled via infrared system for in-bulk measuring. The solution polymerization (with trifluoromethanesulfonic acid as initiator) was possible even at the temperature of 40 °C, yielding PLLA with narrow molecular weight distribution in a very short period of time (less than 6 h). The obtained polymers had the number-average molecular weights ranging from 43,000 to 178,000 g mol⁻¹ (polydispersity index ranging from 1 to 3) according to the gel permeation chromatography measurements. The polymer structure was characterized by Fourier transform infrared and NMR spectroscopy. Thermal properties of the obtained polymers were investigated using thermogravimetry and differential scanning calorimetry.     

Biodegradability,hydrolytic degradability,and builder performance in detergent formulations of partially dicarboxylated alginic acid

Partially dicarboxylated alginic acids with degree of dicarboxylations from 13 to 61 mol% were prepared and their biodegradability, hydrolytic degradability, and builder performances in detergent formulations were measured. Also, the correlations between biodegradability and hydrolytic degradability were examined with respect to the degree of dicarboxylation. The biodegradability of dicarboxylated alginic acid sodium salt (DCAa), evaluated by biochemical oxygen demand with activated sludge, depended on the degree of dicarboxylation. DCAa containing more than 75 mol% remaining uronide residues in the polymer chain showed excellent biodegradation. Hydrolytic degradation of DCAa depended on the degree of dicarboxylation and the pH of the incubation media. After 30-day incubation at 30°C at pH 4–6, a significant molecular weight reduction by hydrolytic degradation was observed for highly dicarboxylated alginic acid. DCAa with a high degree of dicarboxylation showed excellent builder performance in detergent formulations based on the detergency and calcium sequestration capacity.     

Reactively Compatibilized Cellulosic Polylactide Microcomposites

Poly(lactic acid) (PLA) possesses a suite of favorable material properties that are enabling its penetration into diverse markets (e.g., as packaging material or textile fibers). In order to increase the range of applications for this material, it is necessary to modify its properties and for certain applications, reduce its cost. The introduction of fibers into a polymeric matrix is an established route towards property enhancement provided good dispersion and intimate interfacial adhesion can be achieved. In addition, cellulosic microfibers are obtainable at low to moderate cost. In this study, reactive compatibilization of cellulosic fibers with PLA is pursued. Hydroxyl groups available on the surface of cellulosic fibers are used to initiate lactide polymerization. Various processing strategies are investigated: (1) blending preformed PLA with the fiber material, (2) through a one-step process in which lactide is polymerized in the presence of the fibers alone, or (3) reactive compatibilization in the presence of preformed high molecular weight polymer. The results show that materials prepared by simultaneous introduction of lactide and preformed high molecular PLA at the beginning of the reaction possess superior mechanical properties compared to composites made by either purely mechanical mixing or solely polymerization of lactide in the presence of fibers. The modulus of materials containing 25% fibers which are prepared by reactive compatibilization of 30% preformed PLA and 70% lactide (30/70 P/L) improves by 53% compared to the homopolymer, whereas 36% reinforcement can be achieved upon purely mechanical mixing. A further increase to 35% fiber loading leads to a reduction in modulus due to an excess in initiating groups. The same trend was observed in systems containing 65% preformed PLA and 35% lactide (65/35 P/L) with an overall achievable reinforcement that was slightly lower.     

Changes in carbonyl index and average molecular weight on embrittlement of enhanced-photodegradable polyethylenes

Weathering behavior of two types of enhanced-photodegradable polyethylenes was studied using FTIR spectroscopy, tensile property changes, and gel-permeation chromatography to monitor structural changes accompanying photodegradation. Changes in elongation at break and carbonyl index during degradation showed a strong correlation with the average molecular weight of the polymers. At the point of embrittlement, the highest extent of degradation measured using tensile properties, the number-average molecular weights for both polymers were in the 10⁴ g/mol range. Facile biodegradation is not expected of polyethylenes of this degree of polymerization.     

Synthesis of Molecular Imprinting Polymers Separating Toluic Acid Isomers (II)

Polymers that can separate toluic acid isomers were synthesized by molecular imprinting technique. Molecular imprinting polymers (MIPs) for each isomer of toluic acids (TA) were synthesized using styrene and 4-vinylpyridine (4-Vpy). The adsorption characteristics of TA isomers, salicylic acid (SA), and benzoic acid (BA) on each MIP were investigated. The materials used for polymerization of TA isomers MIPs were adsorbed relatively well. This verifies that the MIPs which can adsorb template selectively were synthesized. In addition, the quantities of adsorbed TA isomers on the TA isomers MIPs and on the control polymer polymerized without template were compared and discussed. The variation of adsorption ability for MIPs with repeated use was investigated, showing excellent reproducibility.     

聚硅酸氯化铝镁的制备及絮凝性能

用聚合硅酸、聚合氯化铝和硫酸镁复合制备复合絮凝剂聚硅酸氯化铝镁。SEM分析结果表明,聚硅酸氯化铝镁为交联的枝杈状聚集态。FTIR仪分析表明,聚铝离子及水解络合离子可与共存的聚硅酸聚合形成配位键。以实际废水为处理对象,比较了自制复合絮凝剂聚硅酸氯化铝镁与市售聚合氯化铝的絮凝效果。实验结果表明:在聚硅酸氯化铝镁加入量为40mg/L、废水pH为3的条件下,以自制聚硅酸氯化铝镁为絮凝剂时废水的COD、BOD5、TP、TN、浊度去除率均较高;自制复合絮凝剂聚硅酸氯化铝镁的废水处理效果均优于市售聚合氯化铝。     

Ring-Opening Polymerization of Cyclic Esters onto Liquefied Biomass

Ring-opening polymerization of cyclic esters (-caprolactone, -valerolactone, and l-lactide) onto liquefied biomass (LB) was conducted to obtain the polyester-type polyol and to regulate the characteristics of LB. IR and ¹H-NMR spectra of the obtained polyol showed that the polymerization was successfully conducted in the presence of acid catalyst, which is used in liquefaction. The molecular weight (M_w), hydroxyl value, and viscosity were controllable by changing the reaction conditions. Polyester-type polyurethane foams with a wide range of properties were prepared from the obtained polyol with the appropriate combinations of foaming agents.     

Enzymatic Degradation of Poly(l-Lactic Acid): Effects of UV Irradiation

Amorphous and crystallized poly(l-lactic acid) (PLLA-A and PLLA-C, respectively) films were prepared, and the proteinase K-catalyzed enzymatic degradation of UV-irradiated and non-irradiated PLLA-A and PLLA-C films was investigated for periods up to 10 h (PLLA-A) and 60 h (PLLA-C). The molecular weights of both the PLLA-A and PLLA-C films can be manipulated by altering the UV irradiation time. The enzymatic weight loss values of the UV-irradiated PLLA films were higher than or similar to those of the non-irradiated PLLA film, when compared with the specimens of same crystallinities. UV irradiation is expected to cause the PLLA films to undergo chain cleavage (a decrease in molecular weight) and the formation of C=C double bonds. It seems that the acceleration effects from decreased molecular weight on enzymatic degradation were higher than or balanced with the disturbance effects caused by the formation of C=C double bonds. After enzymatic degradation, a fibrous structure appeared on the spherulites of the UV-irradiated PLLA-C film. This structure may have arisen from chains containing or neighboring on the C=C double bonds, which were enzymatically undegraded and assembled on the film surface during enzymatic degradation. The results of this study strongly suggest that UV irradiation will significantly affect the biodegradation behavior of PLLA materials in the environment.