Radiation degradation and stability of PBAT: copolymer of aromatic and aliphatic esters

Effect of the exposure of poly(butylene adipate‐co‐terephthalate) (PBAT) to ionizing radiation was studied by means of EPR and diffuse reflection spectroscopy, GC, and gel permeation chromatography. In addition, the influence of radiation‐induced processes on mechanical and rheological properties for the doses in the range 0–200 kGy was investigated. The macroscopic consequences of PBAT irradiation included: crosslinking, chain cleavage, and oxidation, which led to the significant modification of physicochemical features. The crosslinking process occurred even under cryogenic conditions and was confirmed by reduction in melt flow index (MFI), increase in viscosity, and weight‐average molecular weight with increasing dose. Material degradation during long‐term storage was accompanied by deterioration of mechanical properties, increase in MFI, and viscosity reduction. Oxidation of the copolyester had a chain character and increased over time, especially in the case of irradiated PBAT. Despite the presence of aromatic rings dissipating energy, the material is susceptible to ionizing radiation. The regions containing terephthalates are involved in the aging processes; the appropriate mechanisms have been proposed. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46682.     

Swelling behavior of polystyrene networks in some aliphatic esters and linear polystyrene solutions

Summary Polystyrene networks were synthesized by free radical polymerization of styrene in the presence of dibenzoyl peroxide as an initiator, divinylbenzene as a crosslinker at 50 °C in toluene under nitrogen atmosphere. The swelling behavior of the synthesized polystyrene networks were studied at different temperatures in methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate, tert-butyl acetate, and isopentyl acetate. Equations were given for the variation of the polymer-solvent interaction parameter, χ₁₂, as a function of reciprocal absolute temperature in the temperature range from 25 to 75 °C. Polystyrene networks were swollen in linear polystyrene solutions in toluene of different concentrations. Linear polystyrene samples were almost monodisperse and of high molecular weight. The equilibrium swelling degrees were evaluated using the Flory-Rehner theory. The relation of volume swelling ratio, q_v, to the volume fraction of the linear polymer in solution, φ, was evaluated and characterized by interaction parameter of crosslinked polystyrene with linear polystyrene, χ₂₃. The parameter χ₂₃ was found around zero as expected from mixtures of similar chemical structures by extrapolating the values of χ₂₃ at tested concentrations to zero solvent concentration.     

The effect of temperature on the in vitro formation of methyl esters in mouse liver

The appearance of methyl esters of fatty acids in lipid extracts was studied. Experimental evidence indicates that these esters are both natural components of tissues as well as products of technical manipulation. Effect of temperature on the latter process was studied. The results of these experiments show that the post-mortem increase of fatty acid methyl esters could best be explained by postulating an enzymatic rather than a chemical process.     

PLGA‐based in situ‐forming system: degradation behavior in the presence of hydroxyapatite nanoparticles

The degradation behavior of poly(lactic‐co‐glycolic acid) (PLGA) is important for its application as a biomaterial. In this work, the influence of nano‐hydroxyapatite (nano‐HA) on the degradation behavior of PLGA matrix was studied. PLGA‐based in situ forming system containing nano‐HA was prepared using the immersion precipitation method and the polymer hydrolysis was investigated in a phosphate buffer (pH 7.4) at 37°C. The pH values in the testing medium were evaluated to quantify the degradation process. Gel permeation chromatography and scanning electron microscopy techniques were employed to monitor changing of the weight‐average molecular weight (M_W) and the body structures of PLGA matrices, respectively. To model the M_W changes, a first‐order degradation model was employed. The formed PLGA matrices had different porosities that effected water penetration into the matrices following the hydrolysis process. The obtained degradation rate constant using a mathematical model for PLGA matrices with different nano‐HA content was about from 2.5 to 4.5 times lower than neat PLGA matrix. POLYM. ENG. SCI., 59:1028–1035, 2019. © 2019 Society of Plastics Engineers     

Biodegradable aliphatic/aromatic copoly(ester-ether)s: the effect of poly(ethylene glycol) on physical properties and degradation behavior

A series of high molecular weight copolymers based on poly(L-lactic acid) (PLLA) as the biodegradable aliphatic segments, poly(butylene terephthalate) (PBT) as the rigid aromatic segments and hydrophilic poly(ethylene glycol) (PEG) as the soft segments were synthesized with the aim of developing novel polymer materials which could combine high physical properties with good biodegradability. Via direct melt polycondensation of terephthalic acid (TPA), 1,4-butanediol (BDO), poly(L-lactic acid) oligomer (OLLA) and PEG, biodegradable aliphatic/aromatic copoly(ester-ether)s, poly(butylene terephthalate-co-lactate-co-ethylene glycol) (PBTLG), were prepared. The effect of the introduction of PEG soft segments on the synthesis, mechanical properties and thermal stabilities as well as the degradation behaviors of the final copolymers was investigated. When the PEG units were incorporated into the polymer main-chains, the weight-average molecular weight of the copolymers increased from 53,700 g/mol to 177,000 g/mol and the tensile strength (σ) improved by nearly two times from 6.5 MPa to 12.8 MPa for PBTLG1000-0.5. The glass-transition temperature (T _g) gradually decreased from 26.9 °C down to −5.5 °C and a depression of melting temperature was observed with the increase of PEG content. According to the in vitro hydrolytic degradation observation, all of the copolymers underwent significant degradation in phosphate buffer solution at 37 °C and the water absorption as well as the degradation rate of PBTLGs displayed a strong dependency on the PEG content.     

原位聚合聚乳酸基纳米复合材料及其降解行为

采用微波技术替代传统热源,以D,L-丙交酯为原料,加入纳米有机蒙脱土(OMMT)及增塑剂聚乙二醇(PEG)进行原位插层聚合制备聚乳酸(PLA)/OMMT/PEG纳米复合材料。在微波功率90 W下作用10 min,w(OMMT)和w(PEG)分别为1%,0.8%时,复合材料拉伸强度达15.39 MPa,拉伸断裂应变为11.67%,热失重中心温度提高6.6℃。形貌分析结果表明,OMMT以剥离形态均匀分散于PLA中,复合材料趋向于韧性断裂。土壤填埋实验结果表明,该复合材料具备更好的降解性能。     

Studies on the autoxidation of nonbranched aliphatic monocarboxylic acids and their methyl esters

Valeric, caproic, and heptanoic acid and their methyl esters were oxidized at 140°C by molecular oxygen. The oxidation mixtures were reduced by LiAlH₄ and the mono- and dihydroxy compounds formed were analyzed gaschromatographically. From the results obtained one can conclude that nonbranched aliphatic acids and their methyl esters are attacked by the chain-carrying peroxy radicals at the different C H bonds with almost the same regioselectivity as normal paraffins Only the ß- and to a smaller extent the α-positions are desactivated by the neighbouring carboxylic group.     

Complexity of the hydrolytic degradation of aliphatic polyesters

Aliphatic polyesters are more or less hydrolytically degradable, depending on their chemical, configurational and morphological structures. Hydrolysis can be either homogeneous or heterogeneous, depending on many structural and environmental factors. The present understanding of this hydrolytic degradation is recalled. The importance of diffusion-reaction phenomena is discussed on the basis of the behaviors of polyesters derived from α-hydroxy acids, namely lactic and glycolic acids and attempts are made to extend the understanding to other members of the aliphatic polyester family. The main results of some recent investigations of the effects on poly(lactic acid) polymers of basic additives and of initiators such as stannous octoate and zinc metal, which are now industrially used, are presented.     

Melting and crystallization behavior of aliphatic polyketones

The basic crystallization and melting behavior of three aliphatic polyketones were studied using differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), small‐angle X‐ray scattering (SAXS), and optical microscopy. One resin was a perfectly alternating copolymer of ethylene and carbon monoxide, while the other two resins were terpolymers in which 6 mol % propylene was substituted for ethylene. Small decreases in the melting point and percent crystallinity of these materials were displayed with repeated melting. This behavior was attributed to light crosslinking as a result of condensation reactions occurring at temperatures in the melting range. WAXS showed that, after cooling to room temperature, the crystalline form in the copolymer was the α‐phase, while that in the terpolymers was the β‐phase. Optical microscopy revealed that the materials produce both negative and mixed birefringence spherulites under the conditions studied. SAXS measurements showed that the lamella thickness was largely a function of the temperature of crystallization. Attempts were made to measure the equilibrium melting temperature of these resins using several available techniques. The best value of the equilibrium melting temperature was concluded to be 278 ± 2°C for the copolymer. The results varied over a wide range for the terpolymers, but it is suggested that appropriate values are of order 252°C for the terpolymers. Crystallization kinetics studies, carried out under isothermal conditions using DSC, were evaluated using the Avrami equation. Results showed the Avrami exponent to lie in the range of 2–3. Spherulite growth rates were interpreted in terms of the secondary nucleation theory of Lauritzen and Hoffman. A transition from regime II to regime III was discovered. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2124–2142, 2002     

PLGA-based gene delivering nanoparticle enhance suppression effect of miRNA in HePG2 cells

The biggest challenge in the field of gene therapy is how to effectively deliver target genes to special cells. This study aimed to develop a new type of poly(D,L-lactide-co-glycolide) (PLGA)-based nanoparticles for gene delivery, which are capable of overcoming the disadvantages of polyethylenimine (PEI)- or cationic liposome-based gene carrier, such as the cytotoxicity induced by excess positive charge, as well as the aggregation on the cell surface. The PLGA-based nanoparticles presented in this study were synthesized by emulsion evaporation method and characterized by transmission electron microscopy, dynamic light scattering, and energy dispersive spectroscopy. The size of PLGA/PEI nanoparticles in phosphate-buffered saline (PBS) was about 60 nm at the optimal charge ratio. Without observable aggregation, the nanoparticles showed a better monodispersity. The PLGA-based nanoparticles were used as vector carrier for miRNA transfection in HepG2 cells. It exhibited a higher transfection efficiency and lower cytotoxicity in HepG2 cells compared to the PEI/DNA complex. The N/P ratio (ratio of the polymer nitrogen to the DNA phosphate) 6 of the PLGA/PEI/DNA nanocomplex displays the best property among various N/P proportions, yielding similar transfection efficiency when compared to Lipofectamine/DNA lipoplexes. Moreover, nanocomplex shows better serum compatibility than commercial liposome. PLGA nanocomplexes obviously accumulate in tumor cells after transfection, which indicate that the complexes contribute to cellular uptake of pDNA and pronouncedly enhance the treatment effect of miR-26a by inducing cell cycle arrest. Therefore, these results demonstrate that PLGA/PEI nanoparticles are promising non-viral vectors for gene delivery.     

Thermal degradation of cellulose and cellulose esters

Cellulose, cellulose diacetate (CDA), cellulose triacetate (CTA), cellulose nitrate (CN), and cellulose phosphate (CP) were subjected to dynamic thermogravimetry in nitrogen and air. The thermostability of the cellulose and its esters was estimated, taking into account the values of initial thermal degradation temperature T_d, the temperature at the maximum degradation rate T_dm, and char yield at 400°C. The results show that these polymers may be arranged in the following order of increasing thermostability: CN < CP < regenerated cellulose < filter cotton < CDA < CTA. The activation energy (E), order (n), and frequency factor (Z) of their degradation reactions were obtained following the Friedman, Chang, Coats–Redfern, Freeman–Carroll, and Kissinger methods. The dependence of T_d, T_dm, E, n, Ln Z, and char yield at 400°C on molecular weight and test atmosphere is also discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:293–304, 1998     

Investigation of the synergistic effect of red phosphorus and magnesium hydroxide on the thermal degradation behavior and flame resistance of the intumescent fire-retardant polypropylene system

High fire-resistance polypropylene (PP) composites were prepared by using environment-friendly flame retardants including expandable graphite (EG), red phosphorus (RP), and magnesium hydroxide (MH). Synergism between EG, RP, and MH on the thermo-oxidation behavior and flame resistance of PP was found. The incorporation of MH and RP formed highly thermally stable mixtures of magnesium phosphates consisting of Mg₃(PO₄)₂, Mg(PO₃)₂, and α-Mg₂P₂O₇ at both amorphous and crystalline phases in the burning process. The mixture not only covered the surface of burning materials but also could reinforce the char structure of the PP/EG composites, thereby significantly enhancing the condensed phase flame retardant mechanism of the composites. Mass ratios of the flame retardants were also optimized to obtain the composite with the highest flame retardant efficiency. The result revealed that the combination of EG, RP, and MH in PP at MH/RP mass ratio of 3/2 with only a total additive content of 18 wt.% could make its limiting oxygen index (LOI) increase from 16.8% to 27.2% and the UL-94 rating was improved from none to V-0. In addition, the mechanical properties of the composites were improved via the surface treatment of MH and RP with calcium stearate and silicone oil, respectively.     

Synthesis and enzymatic degradation of regular network aliphatic polyesters

Regular network aliphatic polyesters were prepared from glycerol (Yg) and a series of various length aliphatic dicarboxylic acids (HOOC-(CH2)_n−2-COOOH, n = 4–10, 12 and 14). Prepolymers prepared by melt polycondensation were cast from dimethylformamide solution and post-polymerized at 230°C for various times to form a network. The resultant films were transparent, flexible and insoluble in organic solvents. The degree of reaction (D_R) estimated from the infrared absorbance of -OH and >CH₂ or >CH groups increased with increasing post-polymerization time and length of methylene chain. The heat distortion temperature also increased with increasing post-polymerization time and was 55, 28, 15, 6, 0, −1, −5, 4 and 32°C for Yg4, Yg5, Yg6, Yg7, Yg8, Yg9, Yg10, Yg12 and Yg14 post-polymerized for 4 h, respectively. Wide angle X-ray scattering patterns showed a distinct single diffraction peak, suggesting some ordered structure due to the establishment of a regular network. Density, water absorption and weight loss by alkali hydrolysis decreased with increasing methylene chain length. The enzymatic degradation was estimated by weight loss of the network films in a buffer solution of lipase at 37°C. The films of Yg4, Yg5, Yg6 and Yg7 showed no weight loss, but the weight loss increased greatly for Yg8, Yg9 and Yg10, and then decreased abruptly for Yg12 and Yg14. This suggests that the enzymatic degradation is affected by network structure, which allows the lipase to penetrate, and by the concentration of the enzymatically degradable ester linkage.     

Synthesis of amines from higher aliphatic esters,ammonia and hydrogen

• 1.1. A study was made of the effect of operational parameters on amination of esters on a fused iron catalyst. Conditions were found to obtain aliphatic amines with a yield of up to 85–86%.
• 2.2. During amination of aliphatic esters both the acid and the alcoholic group of the initial ester take part in the formation of amines.

     

Study on the enzymatic degradation of aliphatic polyester–PBS and its copolymers

The catalytic degradation of prepared matrix poly(butylene succinate) (PBS) and its copolymers by immobilized lipase is carried out in the mixed organic solvent containing a small amount of water. The degradation products were studied with various characterizations techniques, including gel permeation chromatography (GPC), time of flight mass spectrum (TOF‐MS), nuclear magnetic resonance (NMR), and Fourier transform‐infrared spectroscopy (FT‐IR). The results showed that under atmospheric pressure, 60°C, after 24 h catalytic degradation of PBS and its copolymers by immobilized lipase, the yellow oil‐like degradation products can be obtained. The lipase has catalytic activity on various copolymers. At the first time, the monomer of BDO was found in the degradation products and the molecular weight of product with aromatic smell is below 1000. The products consisted of cyclic oligomer, linear oligomer and monomers, and cyclic oligomer is at least dimmer. The minimum and maximum degradation yields correspond to PBS (40%) and P(BS‐co‐CL‐co‐CHDM) (54%). © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The role of nanofillers on the degradation behavior of polylactic acid

This study examines the effect of type and content of various nanofillers on the aging behavior of polylactic acid (PLA)/nanocomposites compared with that of pristine PLA, under specific environmental conditions, namely 80% relative humidity, 40°C temperature, and exposure time up to 6 months. Two different types of nanosized fillers (silica and montmorillonite, MMT) at three different weight fractions as well their mixtures were used for this purpose. The role of the various nanofillers on the aging of pristine PLA and its nanocomposites was investigated in terms of several experimental techniques including Scanning Electron Microscopy (SEM), Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA), and tensile testing. All studied samples, except those of PLA/MMT/Si nanocomposites, exhibited the same trend in properties during aging. In particular, no significant changes are noted after 1 month of aging. The materials after 3 months of aging experienced a dramatic lowering of the stress–strain curve, whereas at 6 months a reverse effect was observed. Comparing the effect of nanofiller types on the degradation, one could conclude that PLA/MMT nanocomposites exhibit a more homogeneous degradation effect, having a higher impact on yield stress in comparison with silica. In contrast, silica has a greater effect in Young's modulus and strain at break, compared with MMT. The peculiar behavior of the PLA/MMT/Si nanocomposites during aging is explained by the hindering action of the mixture of the two nanofillers on the molecular reordering of the PLA chains in the amorphous region. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

脂肪族聚醚型聚氨酯弹性体热降解机理及热稳定性

采用酯交换缩聚法,以聚四氢呋喃醚二醇（PTMEG）和1,6-六亚甲基二氨基甲酸甲酯（HDU）为原料,以1,4-丁二醇（BDO）为扩链剂,以二丁基氧化锡为催化剂制备脂肪族聚醚型聚氨酯（PU）弹性体。用TGA和FTIR考察聚氨酯弹性体的热降解机理及原料组成对聚氨酯热降解过程的影响。结果表明：聚氨酯弹性体的热降解过程包括两个阶段,分别为硬段（氨基甲酸酯）和软段（聚醚多元醇）的降解,其中硬段（氨基甲酸酯）的降解主要降解产物为碳化二亚胺、CO₂、四氢呋喃及水,软段（聚醚多元醇）的降解主要产物为四氢呋喃和水。随着硬段含量的降低,聚氨酯弹性体初始热降解温度由282℃上升至327℃,聚氨酯弹性体的热稳定性升高。     

Waterborne polyurethane: the effect of the addition or in situ formation of silica on mechanical properties and adhesion

A series of composites consisting of commercial waterborne polyurethane (PU) and silica were prepared by in situ synthesis (sol-gel method) and compared to those prepared by the addition of commercial silica (blending method). Adhesion resistance, mechanical resistance, small-angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) measurements were performed in order to evaluate the effect of silica addition. The adhesion resistance reached a maximum at 3 wt.% of added silica. Comparing the sol-gel composites with the analog composites obtained by the addition of commercial nanosilica, it was observed that although the composites containing commercial silica displayed higher mechanical resistance, better adhesion was obtained with the in situ method. The DSC results showed increasing crystallinity with increasing silica addition.     

Investigation of the molecular transport of aliphatic and aromatic esters into engineering polymer membranes

Molecular transport as manifested by sorption and diffusion of organic esters into engineering polymer membranes, viz. nitrile butadiene rubber, styrene butadiene rubber, ethylene propylene diene terpolymer, neoprene and natural rubber, has been investigated in the temperature range 25–60°C by the sorption gravimetric technique. The sorption equilibrium for ethylene propylene diene terpolymer was lower than those of the other polymers with all the liquids. Diffusion and permeation coefficients were obtained for the polymer-solvent systems and these follow Arrhenius type behaviour in the temperature range investigated.     

Thermal degradation of montmorillonite/aliphatic amine complexes in nitrogen

Montmorillonite (Mont)/aliphatic amine complexes were synthesized using five kinds of aliphatic amine (C₂–C₁₈) hydrochlorides, and their thermal degradation below 1473 K in nitrogen was examined. Raw Mont was used as a reference. The interlayer spacings of the complexes were roughly proportional to the size of amine molecules. The five complexes showed almost the same degradation mode. All the guest amines were released from the host Mont at between 573 and 673 K without any carbon remaining, but their interlayer spacings decreased gradually up to 873 K. The layer structures of Mont and complexes were destroyed just below 1273 K. After destruction, an amorphous phase formed in Mont but not in the complexes. After heating to high temperatures, the crystals deposited in Mont were not necessarily identical to those in the complexes and these differences are attributable to the sodium content.