Fabrication and characterization of biodegradable poly(propylene carbonate)/wood flour composites

Wood flour reinforced poly(propylene carbonate) (PPC) composites were prepared by melt blending followed by compression molding. The effects of reinforcement on the morphology, static and dynamic mechanical properties, and thermal properties of PPC/wood flour composites were investigated. In terms of mechanical properties, wood flour had the significant effect of improving tensile strength and stiffness. Scanning electron microscopic examination revealed good dispersion of wood flour (especially at lower content) in the PPC matrix. Moreover, experimental results indicated that the wood flour addition led to an obvious improvement in the thermal stability of the composites. This paper demonstrates that the incorporation of low‐cost and biodegradable wood flour into PPC provides a practical way to produce completely biodegradable and cost‐competitive composites with good mechanical properties. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 782–787, 2006     

Synthesis and degradation behavior of poly(propylene carbonate) derived from carbon dioxide and propylene oxide

High molecular weight and regular molecular structure poly(propylene carbonate) (PPC) was successfully synthesized from carbon dioxide and propylene oxide. The PPC copolymer structure was an exact alternating copolymer as evidenced by the ¹³C‐NMR technique. Degradative behavior of the PPC was conducted by soil burial and buffer solution immersion (pH = 6) tests, respectively. The results showed that the weight loss of soil buried in PPC films increased more slowly than that immersed in the buffer solution after 6‐month exposure. However, the weight loss of sample immersed in the buffer solution increased rapidly during the first 2 months and reached a value of 4.59%. Water sorption measurement also revealed that the PPC membranes immersed in buffer solution were more hydrophilic than those in soil burial tests. The degradation mechanism of PPC membranes was correlated with the sample morphologies, FTIR, and ¹H‐NMR spectra. The SEM morphologies were consistent with the weight loss and water sorption measurements. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1840–1846, 2004     

Microcellular foaming of poly(phenylene sulfide)/poly(ether sulfones) blends using supercritical carbon dioxide

Microcellular foaming of poly(phenylene sulfide)/poly(ether sulfones) (PPS/PES) blends presents a promising approach to produce high‐performance cellular materials with tailored microstructures and enhanced properties. This study investigated the effects of multiphase blend composition and process conditions on the foaming behaviors and final cellular morphology, as well as the dynamic mechanical properties of the solid and microcellular foamed PPS/PES blends. The microcellular materials were prepared via a batch‐foam processing, using the environment‐friendly supercritical CO₂ (scCO₂) as a blowing agent. The saturation and desorption behaviors of CO₂ in PPS/PES blends for various blend ratios (10 : 0, 8 : 2, 6 : 4, 5 : 5, 4 : 6, 2 : 8, and 0 : 10) were also elaborately discussed. The experimental results indicated that the foaming behaviors of PPS/PES blends are closely related to the blend morphology, crystallinity, and the mass‐transfer rate of the CO₂ in each polymer phase. The mechanisms for the foaming behaviors of PPS/PES blends have been illustrated by establishing theoretical models. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42634.     

Preparation and characterization of biodegradable foams from calcium carbonate reinforced poly(propylene carbonate) composites

Biodegradable foams were successfully prepared from calcium carbonate reinforced poly(propylene carbonate) (PPC/CaCO₃) composites using chemical foaming agents. The incorporation of inexpensive CaCO₃ into PPC provided a practical way to produce completely biodegradable and cost‐competitive composite foams with densities ranging from 0.05 to 0.93 g/cm³. The effects of foaming temperature, foaming time and CaCO₃ content on the fraction void, cell structure and compression property of the composite foams were investigated. We found that the fraction void was strongly dependent on the foaming conditions. Morphological examination of PPC/CaCO₃ composite foams revealed that the average cell size increased with increasing both the foaming temperature and the foaming time, whereas the cell density decreased with these increases. Nevertheless, the CaCO₃ content showed opposite changing tendency for the average cell size and the cell density because of the heterogeneous nucleation. Finally the introduction of CaCO₃ enhanced the compressive strength of the composite foams dramatically, which was associated with well‐developed cell morphology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5240–5247, 2006     

Preparation of conducting composites of polypyrrole using supercritical carbon dioxide

Supercritical carbon dioxide, saturated with pyrrole, was brought into contact with oxidant‐impregnated films of poly(chlorotrifluoroethylene) (PCTFE), crosslinked poly(dimethylsiloxane) (PDMS), poly(methyl methacrylate) (PMMA), and porous crosslinked polystyrene (PS) in order to form conducting composites via the in situ polymerization of pyrrole. The two nonporous hosts—PCTFE and crosslinked PDMS—did not form conducting composites with polypyrrole (PPy). On the other hand, the electrical conductivity of the PPy composites with carbon dioxide‐swollen PMMA and porous PS ranged from 1.0 × 10^?4 S/cm to 3.0 × 10^?5 S/cm. In these two cases, the level of pyrrole polymerized on the surface or in the pores of the host polymer was sufficient to attain the interconnected conducting polymer networks necessary for electrical conductivity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1113–1116, 2003     

Elastomeric foam prepared by supercritical carbon dioxide

Biodegradable elastomer poly[(1,4‐butylene terephthalate)‐co‐(1,4‐butylene adipate)] foam was successfully prepared using supercritical CO₂. The elastomer foam has closed and uniform cell structure with density about 90 g/L. Narrow size distribution with average cell diameter 32 μm were obtained. The foamed balls show rubbery properties and can recover well (>90%) to their original shape quickly after releasing press stress. Cell growth needs to take place at melting state where the migration and orientation of polymer chains are permanently kept without remained force of springback. Some unique phenomena were observed during foaming the elastomer: post‐expansion (about 40%) was obtained after removing the foamed samples from a cylinder mold, which results in forming a ball rather than a cylinder like the mold. This phenomenon was explained by the lower glass transition temperature of the elastomer, in which residual CO₂ foam continuously in the room temperature; and “memory” of internal strength. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44354.     

Chemically foaming of biodegradable poly(propylene carbonate) derived from carbon dioxide and propylene oxide

A composite chemical blowing agent PU8, composed of azodiformamide (AC), N,N′‐dinitroso pentamethylene tetramine (H) and other chemicals, was used to prepare the poly(propylene carbonate) foam material. The decomposition behavior of the blowing agent was investigated. The effect of blowing agent content and the foaming condition on the foaming of poly(propylene carbonate) was studied in detail. The results suggested that 10 phr PU8 is the optimum formulation to afford a desired poly(propylene carbonate) foam. The morphologies and compression strength of the poly(propylene carbonate) foam were studied using a scanning electron microscope and tensile tester, respectively. The foam with a blowing ratio of 16 can be obtained under an optimum foaming condition at 160°C for 30 min. POLYM. ENG. SCI. 46:153–159, 2006. © 2005 Society of Plastics Engineers     

Preparation and properties of biodegradable poly(propylene carbonate)/starch composites

Biodegradable composites of poly(propylene carbonate) (PPC) reinforced with unmodified cornstarch were compounded in a batch mixer followed by compression molding. The effects of reinforcement on the morphology, static and dynamic mechanical properties, as well as thermal properties of PPC/starch composites, were investigated. Tensile tests showed that incorporation of starch improves the stiffness and tensile strength of composites significantly. Scanning electron microscopic examination revealed the existence of good interfacial adhesion between the fillers and PPC matrix. Moreover, experimental results indicated that the starch addition leads to a significant improvement in the thermal stability of the composites. This paper demonstrates that the incorporation of low‐cost and biodegradable cornstarch into PPC provided a practical way to produce completely biodegradable and cost‐competitive composites with good mechanical properties. Polym. Eng. Sci. 44:2134–2140, 2004. © 2004 Society of Plastics Engineers.     

Study on poly(butylene adipate‐co‐terephthalate)/starch composites with polymeric methylenediphenyl diisocyanate

To lower the cost of poly(butylene adipate‐co‐terephthalate) or PBAT, starch was used as a filler in this study. To increase tensile strength of PBAT/starch composites, polymeric methylenediphenyl diisocyanate (pMDI) was used as a compatibilizer. PBAT was melt‐mixed with starch in a kneader, and then the mixtures were compression‐molded. The effects of starch and pMDI content on the tensile strength and elongation at break of PBAT/starch composites were examined. The morphology and biodegradability of the composites in soil were also studied. The tensile strength of PBAT and PBAT/starch composites increases with increasing content of pMDI. The increase of weight average molecular weight of PBAT and improved interaction between PBAT and starch were observed with increasing content of pMDI. The weight average molecular weights of buried PBAT and the composites in soil significantly decrease. Especially, the reduction of the weight average molecular weight of PBAT/starch (70/30) composite is the most significant. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41884.     

聚碳酸亚丙酯/热塑性氧化淀粉的流变、形态和性能

采用熔融共混的方法制备了马来酸酐接枝聚碳酸亚丙酯(PPCMA)/热塑性淀粉(TPS)、PPCMA/热塑性氧化淀粉(TPOS)和PPCMA/ DL-TPOS(铝酸酯预处理的TPOS)复合材料,研究淀粉的氧化以及偶联剂的加入对PPC复合材料流变、形态和性能的影响。加入淀粉后的PPC复合材料拉伸强度有较大提高,红外光谱结果显示淀粉和PPCMA之间形成了氢键作用,这可能是力学性能提高的主要原因;热塑性氧化淀粉与PPCMA基材的界面相容性提高,PPCMA/TPOS复合材料的力学性能、储能模量、损耗模量和复数黏度均高于PPCMA/TPS复合材料;铝酸酯对TPOS的预处理促进了TPOS在PPCMA中的分散,提高了复合材料的拉伸强度,在PPCMA/DL-TPOS体系中,当DL-TPOS含量为40%(质量分数)时拉伸强度达到最大值,与PPCMA相比,提高了4.6倍。     

超临界二氧化碳釜压发泡法制备生物可降解PBAT发泡颗粒

通过超临界二氧化碳釜压发泡技术制备了生物可降解聚对苯二甲酸丁二醇酯?co?聚己二酸丁二醇酯（PBAT）发泡颗粒,采用核磁共振光谱仪（¹H?NMR）、凝胶渗透色谱仪（GPC）、差示扫描量热仪（DSC）对PBAT的化学组分及热性能进行了表征,并研究了渗透条件对PBAT发泡性能的影响。结果表明,PBAT中己二酸丁二醇（BA）和对苯二甲酸丁二醇（BT）链节含量分别为53 %和47 %（摩尔分数）;PBAT的玻璃化转变温度、最大熔融温度和结晶度分别是-33、122 ℃ 和13.16 %,其分解温度为280 ℃;当渗透温度从76 ℃增加到90 ℃时,PBAT发泡颗粒密度逐渐降低、发泡倍率逐渐增大,且该条件下制备的PBAT发泡颗粒放置1 d后密度增加、发泡倍率降低,继续延长放置时间至7 d时,其密度和发泡倍率保持不变;当渗透时间从0.5 h延长到2 h时,PBAT发泡颗粒密度逐渐降低、发泡倍率逐渐增加;当渗透时间从2 h延长到3 h时,其密度和发泡倍率保持不变;当渗透压力从10 MPa增加到12 MPa时,PBAT发泡颗粒密度逐渐降低、发泡倍率逐渐增加;当渗透压力从12 MPa增加到14 MPa时,其密度和发泡倍率保持不变。     

Study of different effects on foaming process of biodegradable PLA/starch composites in supercritical/compressed carbon dioxide

Microcellular foaming of biodegradable and biocompatible PLA/starch composites in supercritical/compressed CO₂ has been studied. The purpose of this study is to explore the potential application of this kind of materials in medical materials or drug containers. The rate of CO₂ uptake and CO₂ equilibrium concentration in PLA/starch composites were studied by performing sorption and desorption experiments. The effects of a series of variable factors, such as saturation time and saturation temperature on the foaming morphology were studied through SEM observation and density measurement. The experimental results show that, while keeping other variables unchanged, longer saturation time leads to reduced bulk foam densities and different saturation pressures result in different bulk foam densities. The crystallinity of PLA–starch sample was characterized by differential scanning calorimetry. It indicates that the foaming treatment with supercritical CO₂ increased the crystallinity of PLA/starch composites. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of chain extrender on the compatibility,mechanical and gas barrier properties of poly(butylene adipate-co-terephthalate)/poly(propylene carbonate) bio-composites

Bio-composites consisting of poly(butylene adipate-co-terephthalate) (PBAT), poly(propylene carbonate) (PPC) and epoxy chain extender ADR 4468 were fabricated via melt blending using a torque rheometer. The relationship of the torque, melt viscosity, and molecular weight of the bio-composites was established via polymeric liquid theory to estimate the real-time chain extension reaction rate under different ADR contents. At the meantime, rheological behavior, thermal and mechanical properties, morphologies, gas barrier properties of the PBAT/PPC/ADR bio-composites were systematically characterized. The corresponding results revealed that the water vapor transmission rate (WVTR) reduced by 50% under 30 phr (parts per hundreds of resin) PPC content. The addition of ADR is beneficial to improve the mechanical properties, thermal stability and phase dispersion of PBAT/PPC without affecting the water barrier property. With 3 phr ADR, the tensile stress and elongation at break were increased from 19.5 MPa and 1184% to 26.9 MPa and 1443%, respectively. In addition, the data of the torque rheometer revealed that the chain extension reaction rate and the melt viscosity was increased with the increasing ADR content, but the reaction rate was reduced with the excessive viscosity.     

Experiment and simulation of foaming injection molding of polypropylene/nano-calcium carbonate composites by supercritical carbon dioxide

Microcellular injection molding of neat isotactic polypropylene (iPP) and isotactic polypropylene/nano-calcium carbonate composites (iPP/nano-CaCO₃H) was performed using supercritical carbon dioxide as the physical blowing agent. The influences of filler content and operating conditions on microstructure morphology of iPP and iPP/nano-CaCO₃H microcellular samples were studied systematically. The results showed the bubble size of the microcellular samples could be effectively decreased while the cell density increased for iPP/nano-CaCO₃H composites, especially at high CO₂ concentration and back pressure, low mold temperature and injection speed, and high filler content. Then Moldex 3D was applied to simulate the microcellular injection molding process, with the application of the measured ScCO₂ solubility and diffusion data for iPP and iPP/nano-CaCO₃H composites respectively. For neat iPP, the simulated bubble size and density distribution in the center section of tensile bars showed a good agreement with the experimental values. However, for iPP/nano-CaCO₃H composites, the correction factor for nucleation activation energy F and the pre-exponential factor of nucleation rate f0 were obtained by nonlinear regression on the experimental bubble size and density distribution. The parameters F and f0 can be used to predict the microcellular injection molding process for iPP/nano-CaCO₃H composites by Moldex 3D.     

Morphology,mechanical properties,and thermal stability of poly(L‐lactic acid)/poly(butylene succinate‐co‐adipate)/silicon dioxide composites

Poly(butylene succinate‐co‐adipate) (PBSA) and two types of SiO₂ (hydrophilic or hydrophobic) were used to modify poly(L ‐lactic acid) (PLLA). The mechanical properties, rheological and thermal behavior, phase morphology, and thermal stability of PLLA/PBSA/SiO₂ composites were investigated. The impact strength, flexural strength, and modulus of PLLA/PBSA blends increased after the addition of hydrophobic SiO₂ without decreasing the elongation at break, and the elongation at break monotonically decreased with increasing hydrophilic SiO₂ content. The melt elasticity and viscosity of the PLLA/PBSA blend increased with the addition of SiO₂. The hydrophilic SiO₂ was encapsulated by the dispersed PBSA phase in the composites, which led to the formation of a core–shell structure, whereas the hydrophobic SiO₂ was more uniformly dispersed and mainly located in the PLLA matrix, which was desirable for the optimum reinforcement of the PLLA/PBSA blend. The thermogravimetric analysis results show that the addition of the two types of SiO₂ increased the initial decomposition temperature and activation energy and consequently retarded the thermal degradation of PLLA/PBSA. The retardation of degradation was prominent with the addition of hydrophobic SiO₂. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation and characterization of poly(glycerol sebacate)/cellulose nanocrystals elastomeric composites

Poly(glycerol sebacate) (PGS) is one of the new elastomers used for soft tissue engineering, while improving its limited mechanical strength is the biggest challenge. In this work, a novel biodegradable elastomer composite PGS/cellulose nanocrystals (CNCs) was prepared by solution‐casting method and the mechanical properties, sol–gel contents, crosslink density, and hydrophilic performance were characterized. The thermal and degradation properties of composites were also investigated. Results show that the addition of CNCs into PGS resulted a significant improvement in tensile strength and modulus, as well as the crosslink density and the hydrophilicity of PGS. When the CNCs loading reached 4 wt %, the tensile strength and modulus of the composite reached 1.5 MPa and 1.9 MPa, respectively, resulting 204% and 158% increase compared to the pure PGS. Prolonging the curing time also improved the strength of both the neat PGS and PGS/CNCs composites according to the association and shift of hydroxy peaks around 3480 cm^?1. DSC results indicate that the addition of CNCs improved both the crystallization capacity and moving capability of PGS molecular chain. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42196.     

Effect of octa(epoxycyclohexyl) POSS on thermal,rheology property,and foaming behavior of PLA composites

Foams of poly(lactic acid) (PLA)/octa(epoxycyclohexyl) polyhedral oligomeric silsesquioxanes (ePOSS) composite were prepared by melt‐mixing and solid‐state foaming methods. A systematic and accurate method was applied to evaluate the effects of epoxy‐based POSS on the structure of dispersion, thermal behavior, and rheological properties of PLA composites. The application of secondary electron–electron back‐scattered diffraction technique was used to observe the cellular micromorphology and micro‐phase dispersion in composite foams, simultaneously. The results indicated that secondary dispersion of POSS aggregates occurred in foaming process. The enhanced melt elasticity, dispersity of POSS, and crystallization morphology of PLA/POSS composite had a significant effect on the controlling foaming behavior. Thus, a homogeneous and finer cellular morphology of PLA/POSS composite foam with high expansion ratio was obtained with a proper content of POSS in the composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46399.     

Iodine doping of poly(3‐undecylbithiophene) and its composites with polystyrene using supercritical carbon dioxide

Partially doped conductive poly(3‐undecylbithiophene) and its composites with porous, crosslinked polystyrene were chemically doped with iodine using supercritical carbon dioxide to transport iodine to the conductive regions of the composite. The amount of iodine incorporated into the composite increased from 9.3 wt % at ambient conditions without carbon dioxide to 21.4 wt % in the presence of supercritical carbon dioxide. The conductivity of the composite increased by up to two orders of magnitude with iodine doping using supercritical carbon dioxide. The highest conductivity was obtained in samples treated at moderate temperatures and pressures (313 K and 20.7 MPa). © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3876–3881, 2003     

Poly(propylene carbonate)/aluminum flake composite films with enhanced gas barrier properties

A series of poly(propylene carbonate) (PPC)/aluminum flake (ALF) composite films with different ALF contents were prepared via a melt‐blending method. Their cross‐section morphologies, thermal properties, tensile strength (TS), and gas barrier properties were investigated as a function of ALF contents. SEM images reveal the good dispersion and orientation of ALF along with melt flow direction within PPC matrix. The oxygen permeability coefficient (OP) and water vapor permeability coefficient (WVP) of the composite films decrease continuously with ALF contents increasing up to 5 wt %, which are 32.4% and 75.2% that of pure PPC, respectively. Furthermore, the TS and thermal properties of PPC/ALF composite film are also improved by the incorporation of ALF particles. The PPC/ALF composite films have potential applications in packaging area due to its environmental‐friendly properties, superior water vapor, and oxygen barrier characteristics. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41663.     

Processing and characterization of supercritical CO2 batch foamed poly(lactic acid)/poly(ethylene glycol) scaffold for tissue engineering application

Both poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG) are biodegradable polymers, blending PLA with PEG is expected to toughen PLA matrix while maintaining its biodegradability. In this study, PLA/PEG blends in different ratios were prepared through triple‐screw extruder, and the foaming behavior was investigated using supercritical carbon dioxide as physical blowing agent. The mechanical, thermal, rheological properties, and crystallization behavior were also studied. By the incorporation of PEG, the impact strength of the PLA/PEG blends improved by 98% with the specimens fractured in a ductile mode. The crystallization process of the blends was accelerated, and the crystallinity was significantly increased to 45.1%. The viscoelasticity of the PLA/PEG matrix was weakened, and the cells tended to break at the cell wall during cell expansion; thus, a highly interconnected structure with a maximum porosity of 82.3% was obtained. Moreover, the PLA/PEG blends exhibited higher cell densities and smaller cell size, compared to their neat counterparts. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3066–3073, 2013