Preparation and Characterization of Composites Based on Poly (Butylene Succinate) and Poly (Lactic Acid) Grafted Tetracalcium Phosphate

Tetracalcium phosphate (TTCP, Ca₄(PO₄)₂O) was functionalized by poly (l-lactic acid) (PLLA) in order to improve the dispersion of TTCP particles in poly (butylene succinate) (PBS) matrices, and then a series of the PLLA grafted TTCP/PBS (g-TTCP/PBS) composites were prepared via melt processing. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), tensile analysis, differential scanning calorimetry (DSC), thermogravimetric analysis (DTG/TGA) and melt rheological analysis were used to investigate the structure and properties of the g-TTCP/PBS composites. The results revealed that l-lactide could be grafted onto the surface of TTCP, and the g-TTCP/PBS composites showed the best mechanical properties when the content of g-TTCP was 10 wt%. The crystallization temperature of g-TTCP/PBS composites tended to increase with the increase of g-TTCP contents. The functionalized particles played an important role in augmenting the thermal degradation rate and the complex viscosity of the composites due to their unique structure and the reasonable interfacial interaction between the particles and PBS matrix.     

Effects of Molecular Weight on Thermal Degradation of Poly(α-methyl styrene) in Nitrogen

The effects of molecular weight on the thermal degradation behavior of poly(α-methyl styrene) (PAMS) was investigated by pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS) and thermogravimetric analysis (TGA). The Py-GC/MS analysis results showed that the degradation of PAMS with different molecular weights in nitrogen produced only the monomer, alpha-methylstyrene. The TGA results showed a pronounced reduction in the decomposition temperature with increasing molecular weight. The degradation kinetic parameters, calculated by the Kissinger and the Coats–Redfern methods, further revealed that the activation energy and the pre-exponential factor decreased with increasing molecular weight. Most importantly, the degradation order of the PAMS in nitrogen remained around 1, independent of the molecular weight, suggesting the maintenance of the depolymerization mechanism. All the above results provided an insight into the effects of molecular weight on the thermal degradation behavior of PAMS.     

Characteristics and Kinetics of Thermal Degradation of Fluoroether Rubber

An advanced, heat-resistant fluoroether rubber (FM-20) was subjected to dynamic thermogravimetric analysis (TGA) in the air atmosphere. The results suggested that its thermal degradation process can be divided into two parts. As the heating rate increased, the initial decomposition temperature and degradation temperature would move to higher ranges. The apparent activation energy of thermal decomposition, calculated by the Kissinger, Friedman and Flynn-Wall-Ozawa methods were 209, 240, and 211kJ/mol, respectively. Furthermore, the probable thermal degradation mechanism was also analyzed by the Coats-Redfern method. As a result, the most reasonable thermal degradation mechanism of FM-20 was g (α) = α^3/2     

Thermal Degradation Behavior and Flame Retardancy of Polycarbonate Containing Poly[(phenylsilsesquioxane)-co-(dimethylsiloxane)] and Potassium Diphenyl Sulfonate

The synergistic effect of poly[(phenylsilsesquioxane)-co-(dimethylsiloxane)] (PPSQDS) and potassium diphenyl sulfonate (KSS) on the thermal degradation and flame retardancy of polycarbonate (PC) was studied. The flame retardancy of PC was improved by the combination of PPSQDS and KSS, and a V-0 rating for 1.6 mm thickness sample was successfully obtained. The thermal degradation of the flame retarded PC was characterized by thermogravimetric analysis (TGA) and the degradation activation energy (E _a) was calculated according to the Kissinger and Flynn-Wall-Ozawa (F-W-O) methods. The E _a value of PC was decreased by the combination of PPSQDS and KSS, indicating that the synergistic effect of PPSQDS and KSS facilitates the thermal degradation of PC and accelerates char formation.     

Thermal Degradation Kinetics of Plasticized Poly (Vinyl Chloride) with Six Different Plasticizers

Plasticized PVC formulated with different kinds of normally used plasticizers, including bis(2-ethylhexyl) phthalate (DOP), dioctyl terephthalate (DOTP), acetyl tri-n-butyl citrate (ATBC), acetyl trioctyl citrate (ATOC), trioctyl trimellitate (TOTM), and a new vegetable devived plasticizer, isosorbide ester (ID-37), were prepared by a melt blending method. The effect of plasticizer on the thermal degradation behavior of plasticized PVC was investigated by thermal gravimetric analysis (TGA). The activation energies were calculated by three well known methods, developed by Flynn-Wall-Ozawa (FWO), Friedman and Kissinger, respectively. The TGA conducted in N₂ atmosphere showed that the type of plasticizer had an obvious influence on the thermal stability of plasticized PVC. It was found that the peak temperatures (T_P) of the thermal degradation processes shifted to higher temperature with the increase of the heating rate, with two processes being shown. The activation energy of the first thermal decomposition process (E₁), calculated by the Kissinger method, was between 118 and 130 kJ/mol, while the activation energy of the second thermal decomposition process (E₂) was between 261 and 305 kJ/mol, except 499 kJ/mol for the PVC/TOTM formulation. The corresponding values of E₁ and E₂ obtained by the Flynn-Wall-Ozawa method were similar to the above data. E of the sample with TOTM also showed a higher value than the others; the results demonstrated that the PVC plasticized with TOTM was more thermally stable than with the others. The activation energies for certain conversion degrees were calculated by the Friedman method and the FWO method. The value of activation energy for 20%, 50%, and 80% conversion calculated by the Friedman method, exhibited an apparent difference from that calculated by the Flynn-Wall-Ozawa method; the results showed that the value of E obtained by the Friedman method was much more reasonable than that obtained by the Flynn-Wall-Ozawa method.     

A Comparative Study on In vitro Degradation Behaviors of Poly(L-lactide-co-glycolide) Scaffolds and Films

In vitro degradation behaviors of three-dimensional porous scaffolds and films made from amorphous poly(L-lactide-co-glycolide) (85/15) were systematically investigated up to 12 weeks in phosphate buffer saline (PBS) solution at 37°C. The following properties of the scaffolds and films were compared as a function of degradation time: pH value of PBS, water uptake, weight, molecular mass and its distribution, and morphology. The results show that the films degraded much faster than the scaffolds. The film's degradation was heterogenous due to the increased concentration of the acidic degradation products inside. However, owing to much thinner pore walls, heterogenous degradation due to the autocatalytic effect was not observed in the scaffolds.     

Influence of Bovine Bone Content on In Vitro Degradation of Poly-L-lactic Acid and Bovine Bone Composite Materials

In vitro degradation experiments of poly-L-lactic acid (PLLA) and bovine bone (BB) composites were carried out in a phosphate-buffered solution (PBS) at 37°C with a pH of 7.4. The influence of BB content on pH value of PBS, water uptake, molecular weights, molecular weight distributions, weight losses, mechanical strengths, and morphologies of PLLA/BB was investigated with degradation times. The results indicated that the presence of the BB modified the degradation of the PLLA matrix. The degradation rate of PLLA in the PLLA/BB composite was slower than the degradation rate of the sole PLLA material. Furthermore, the degradation rate of the composites became slower with the increasing content of BB in PLLA/BB composites.     

Kinetic analysis of thermal and thermo-oxidative degradation of polyethylene (nano)composites

Thermal properties and degradation of polyethylene LDPE (nano)composites were investigated by isoconversional thermogravimetric analysis in air and nitrogen atmosphere by applying the Kissinger–Akahira–Sunose method. Low-density polyethylene (LDPE) composites containing 3 wt.% nanofiller Cloisite 20A and 4, 6, and 8 wt.% of natural zeolite were prepared using extrusion/injection moulding. The parameters of thermal stability of the samples were determined i.e. onset temperature of the degradation (T₉₀), which exhibit initial mass loss (10 mass %) and maximum loss rate temperature (T_max). Also, activation energy (E_a) of samples was calculated and interpreted in terms of thermal degradation mechanisms. Under nitrogen, the thermal degradation of LDPE (nano)composites follows a random scission pathway but it was retarded and slowed by the presence of the fillers. The results show that thermo-oxidative degradation of studied (nano)composites is induced at lower temperatures and appears as much more complex and multi-stage process.     

In-Vitro Degradation Behaviors of Composite Scaffolds Based on 1,4-Butadnediamine Modified Poly(lactide-co-glycolide) and Nanobioceramics

In-vitro degradation behaviors of composite scaffold materials composed of 1,4-butanediamine modified poly(lactide-co-glycolide) (BMPLGA), nanobioactive glass (NBG) and β-tricalcium phosphate (β-TCP) were systematically investigated in phosphate-buffered solution (PBS) at 37?°C. The properties of the BMPLGA/NBG-β-TCP and BMPLGA scaffolds, including the changes of pH value, mass, water uptake, compressive strength and molecular mass, were investigated as a function of degradation time. The results showed that the introduction of the NBG and β-TCP particles played important roles in the degradation of BMPLGA matrix. The degradation rate of the BMPLGA/NBG-β-TCP scaffolds was slower than that of the BMPLGA scaffolds.     

Preparation and In Vitro Degradation Behavior of Poly(L-lactide-co-glycolide) by Direct-Melt Polycondensation

Poly(L-lactide-co-glycolide)(PLGA)copolymer (85/15) was prepared by direct-melt polycondensation instead of a ring-opening process. The polymer samples were hydrolyzed at 37°C in phosphate-buffered saline (PBS) for periods up to 10 weeks and the degradation behavior was characterized through weight average molecular mass change, mass loss, water uptake, and morphology. The results indicate that mass loss, weight average molecular mass, and water uptake of PLGA increase with increasing time; however, pH value of the PBS solution decreases. The degradation is heterogeneous—degradation in their central parts was faster than in the surface and regions due to the increased concentration of the acidic degradation products inside.     

Nonisothermal Degradation Kinetics and Life Prediction of the Pendent Phenyl-Containing Polyarylate

The nonisothermal degradation kinetics of a pendent phenyl-containing polyarylate (PAR-P)were studied using different kinetic models, including the Kissinger method, Flynn–Wall–Ozawa (FWO) method, and Coats–Redfern (CR) method. The “three kinetic factors” of degradation, namely, activation energy (E), pre-exponential factor (A), and the reaction mechanism function (f(α)) were determined by these methods. Moreover, the lifetime equations of PAR-P were deduced, and its lifetime was predicted. The Kissinger method could be used to describe the nonisothermal degradation of PAR-P, and the results indicated that PAR-P could be degraded more easily in air than in nitrogen. The FWO method was expected to give more reliable values of the activation energy (209.71 kJ·mol^?1 in nitrogen and 176.22 kJ·mol^?1 in air) due to not having to introduce the reaction mechanism function during the calculation. According to the results of the CR method, the thermal degradation reaction mechanism was probably the R1 model in nitrogen, while it was likely to be the F2 model in air. The long-term and short-term use temperatures of PAR-P in air were 260°C and 300°C, respectively. The lifetime of PAR-P in nitrogen was much longer than that in air at low temperature, but had little difference when the use temperature exceeded 260°C. Although the lifetime of PAR-P obtained from the present work was unrealistic due to probable contributions from other unconsidered factors and being determined by a single factor method, it still could play a guiding role for designing the structure and determining the use conditions of the material.     

Fabrication of Poly(D,L-lactide-co-glycolide) Microspheres and Degradation Characteristics in vitro

Poly(D,L-lactide-co-glycolide) (PLGA, 75/25) microspheres were prepared by the emulsion solvent extraction/evaporation technique and their degradation behaviors in vitro at 37°C were investigated. PLGA microspheres with a smooth and nonporous surface were obtained, with a mean particle size of 114.15 μm. It was observed that mass loss and water uptake of PLGA increased with increasing degradation time; however, weight average molecular weight and the pH value of the phosphate buffered saline (PBS) solution decreased. The observed relative rates of mass loss vs. molecular weight decreases were consistent with the explanation that PLGA underwent bulk degradation rather than surface degradation. During the degradation time, the surface of the PLGA microspheres became coarse and there were many micropores that developed upon immersion in the PBS. The microspheres lost their spherical form with increasing degradation time.     

Sequential Structure,Crystallization, and Properties of Biodegradable Poly(ethylene Terephthalate-Co-Ethylene Oxide-Co-Lactide) Copolyester

The sequential structure, isothermal crystallization, tensile property, and degradation behavior of poly(ethylene terephthalate-co-ethylene oxide-co-lactide) (ETOLA) copolyester based on melt transesterification of poly(ethylene terephthalate) with poly(ethylene oxide) and oligo(lactic acid) was investigated. The degree of randomness was calculated to be 0.38, showing the incorporation of poly(ethylene oxide) (PEO) blocks into the homogeneous sequences of ethylene terephthalate (ET) and lactide (LA) units. The isothermal crystallization kinetics results revealed that the crystallization activation energy of the copolyester calculated using the Arrhenius’ equation was lower than that reported for poly(ethylene terephthalate) (PET), indicating that the addition of PEO and LA units into PET retarded the crystallization of PET. The copolyester exhibited the same crystal structure at different crystallization temperatures, similar to that of PET homopolymer, based on wide angle X-ray diffraction results. The size of the spherulites of ETOLA increased with crystallization temperature. The increase of crystallization temperature reduced the elongation at break of the copolyesters, as well as the enzymatic degradation.     

聚甲基丙烯酸甲酯热氧化降解的化学动力学研究

使用质谱、热分析手段研究了PMMA热解反应 .结果表明 ,在氮气中 ,PMMA -CH =CH2 有两个失重阶段 ,分别对应于主链末端双键引发的断链和主链无规则断链反应 ,转折点的失重率约为 2 6 % .其中 ,第一阶段的失重速率受扩散过程控制 ,平均表观活化能E为 15 8.5kJ/mol,lnA为 2 7.6 9;第二失重阶段为 1.5级化学反应 ,平均表观活化能E为 2 14 .79kJ/mol,lnA为 4 0 .4 6 .在空气中 ,PMMA也有两个失重阶段 ,反应机理为 1级化学反应 ,转折点处的失重率约为 70 % .其中在第一失重阶段平均表观活化能E为 130 .32kJ/mol,lnA为 2 4 .81,在此阶段中 ,过氧化基团的分解反应对PMMA的失重速率有重要影响 ;在空气中第二失重阶段平均表观活化能E为 78.2 5kJ/mol,lnA为 13.97.     

Kinetics of sono-photooxidative degradation of poly(alkyl methacrylate)s

The mechano-chemical degradation of poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA) and poly(n-butyl methacrylate) (PBMA) using ultrasound (US), ultraviolet (UV) radiation and a photoinitiator (benzoin) has been investigated. The degradation of the polymers was monitored using the reduction in number average molecular weight (M(n)) and polydispersity (PDI). A degradation mechanism that included the decomposition of the initiator, generation of polymer radicals by the hydrogen abstraction of initiator radicals, reversible chain transfer between stable polymer and polymer radicals was proposed. The mechanism assumed mid-point chain scission due to US and random scission due to UV radiation. A series of experiments with different initial M(n) of the polymers were performed and the results indicated that, irrespective of the initial PDI, the PDI during the sono-photooxidative degradation evolved to a steady state value of 1.6±0.05 for all the polymers. This steady state evolution of PDI was successfully predicted by the continuous distribution kinetics model. The rate coefficients of polymer scission due to US and UV exhibited a linear increase and decrease with the size of the alkyl group of the poly(alkyl methacrylate)s, respectively.     

Isothermal Crystallization and Melting Behavior of Composites Composed of Poly(L-lactic Acid) and Poly(glycolic Acid) Fibers

Several composites of poly (L-lactic acid) (PLLA) with poly (glycolic acid) (PGA) fibers were prepared. The isothermal crystallization kinetics and melting behavior of PLLA and all of the composites were characterized by using differential scanning calorimetry. The experimental data were processed by using the Avrami equation. The relative parameters, such as the Avrami exponent and half-time crystallization, revealed that PGA fibers had positive effects on the crystallization of PLLA, but these effects had only a minimal dependence on the PGA fiber content. Moreover, at low isothermal crystallization temperatures (85°C～110°C), recrystallization during the heating scan was observed, which could lower the melting point of the samples to a certain extent.     

Thermal Stability and Decomposition Kinetics of Poly(Methacryloyloxyethyl Trimethyl Ammonium Chloride-Co-Acrylamide)

Abstract

Poly(methacryloyloxyethyl trimethyl ammonium chloride-co-acrylamide) (P(DMC-AM)), is widely used for various applications under a wide range of conditions. In this work the thermal stabilities and decomposition kinetics of P(DMC-AM) with various intrinsic viscosities, synthesized in our laboratory, were studied by thermogravimetric analysis (TGA) at various heating rates, 5, 10, 20 and 40?K/min, and differential scanning calorimetry (DSC) at 10?K/min, all under a dynamic nitrogen atmosphere. The kinetic parameters were calculated using a model fitting method (Coats–Redfern, CR) and two model–free methods (Kissinger–Akahira–Sunose, KAS and Flynn–Wall-Ozawa, FWO). The result showed that all samples exhibited three steps of mass loss, one for the elimination of the adsorbed water and organic solvents and two for the thermal decomposition of P(DMC-AM). The first decomposition stage for the three samples was in the range of 5% to 45%, the second decomposition stage in the range of 65% to 95% and with 55% conversion separating the first and second decomposition stages. The E values increased with the increasing intrinsic viscosity of the samples. Hence, P(DMC-AM) had good thermal stability and the higher the molecular weight, the better the thermal stability was.     

Effect of Annealing Poly(4-Methylpentene) and of Oxidative Degradation during Annealing

Injection molded specimens of a poly(4-methylpentene) (TPX) were annealed at temperatures between 140 and 220°C for times up to 500 min in air, and the annealed TPX specimens were characterized by the differential scanning calorimeter, UV–visible spectrometry, FT-IR, and X-ray diffraction. The annealing of the TPX specimens at 140–180°C for 50 min showed little effect on their thermal properties. However, the thermal properties were significantly affected by annealing at 200–220°C, and the change was dependent on the annealing time. Besides the annealing effect, the thermal properties were also affected by oxidative degradation. Severe oxidative degradation can destroy the crystalline structure and thus decreases the crystallinity. The oxidative degradation phenomenon of the TPX specimens during annealing can be simulated by isothermal scanning of the weight loss in air by thermal gravimetric analysis.     

Formation of Ring-Banded Spherulites of Poly (L-lactide) in its Miscible Mixture with an Ionic Liquid

Incorporation of an ionic liquid, nonvolatile and thermally stable, promoted formation of ring-banded spherulites in poly (l-lactide) (PLLA) during its sol–gel transition. Their formation is correlated with low viscosity and insignificant chain entanglements in the mixtures induced by the ionic liquid. In addition to a driving force for lamellar twisting that depended on the crystallization temperatures, it is believed that reduced lamellar twisting resistance caused by the ionic liquid plays a vital role in the formation of the ring-banded spherulites of PLLA from the mixtures. This study gives further insights into the structural formation of PLLA during a sol–gel transition, which could open new opportunities to tailor the properties of ion gels based on PLLA.