Preparation and characterization of poly(propylene carbonate)/montmorillonite nanocomposites by solution intercalation

Poly(propylene carbonate) (PPC) is a new biodegradable aliphatic polycarbonate. However, the poor thermal stability and low glass transition temperatures (T_g) have limited its applications. To improve the thermal properties of PPC, organophilic montmorillonite (OMMT) was mixed with PPC by a solution intercalation method to produce nanocomposites. An intercalated-and-flocculated structure of PPC/OMMT nanocomposites was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thermal and mechanical properties of PPC/OMMT nanocomposites were investigated by thermal gravimetric analysis (TGA), differential scanning calorimetric (DSC), and electronic tensile tester. Due to the nanometer-sized dispersion of layered silicate in polymer matrix, PPC/OMMT nanocomposites exhibit improved thermal and mechanical properties than pure PPC. When the OMMT content is 4 wt%, the PPC/OMMT nanocomposite shows the best thermal and mechanical properties. These results indicate that nanocomposition is an efficient and convenient method to improve the properties of PPC.     

氯化聚丙撑碳酸酯增容聚丙撑碳酸酯/秸秆粉复合材料的制备及性能

聚丙撑碳酸酯(PPC)是一种新型热塑性生物降解材料,但其热性能及力学性能较差,应用受到限制。以秸秆粉这种农作物副产品作为增强体改性PPC,既可以提高PPC的力学性能同时又可开发利用秸秆资源。氯化聚丙撑碳酸酯(CPPC)是聚丙撑碳酸酯(PPC)经过氯化得到的,对天然纤维表面具有良好的浸润性和粘结性。本文以CPPC为增容剂,通过熔融共混法制备了PPC/秸秆粉复合材料。采用扫描电子显微镜(SEM)、拉伸实验、动态力学性能测试(DMA)及转矩流变仪对复合材料的结构及性能进行了表征,重点考察了CPPC的添加量对复合材料力学和流变性能的影响。结果表明,当CPPC质量分数为1.8%时,可使添加质量分数为30%秸秆粉的PPC复合材料拉伸强度提高38%,模量提高30%。同时,CPPC的引入使复合材料的粘度下降,改善了PPC/秸秆粉复合材料的加工性能。因此,作为增容剂的CPPC为制备高性能PPC/天然纤维复合材料提供了新的解决办法。     

Modification of poly(propylene carbonate) with chain extender ADR-4368 to improve its thermal,barrier, and mechanical properties

Melt blending with the application of epoxy compound ADR-4368 as a chain extender was used to chemically modify polypropylene carbonate (PPC). ¹H nuclear magnetic resonance spectroscopy (¹H NMR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and tests using a universal material testing machine, a gas permeability tester, a water vapor permeability tester and other instruments were used to assess changes in the chemical structure, thermal and mechanical properties, and barrier efficacy of PPC before and after modification.The epoxy group in ADR-4368 reacted with the terminal hydroxyl group in PPC, considerably enhancing its mechanical properties, thermal stability and barrier efficacy to O₂ and CO₂. With the addition of 1% ADR-4368, the glass transition temperature of PPC was increased from 17 °C to 26.9 °C, while the thermal decomposition temperature (T_−5%) of PPC was increased from 177.3 °C to 240.6 °C. Moreover, the tensile strength of the modified PPC was improved from 3.3 MPa to 20.7 MPa.     

Electron-beam irradiation on poly(propylene carbonate) in the presence of polyfunctional monomers

Poly(propylene carbonate) (PPC) showed predominantly degradation under electron-beam irradiation, accompanied by deterioration of its mechanical performance due to sharp decrease of the molecular weight. Crosslinked PPC was prepared by addition of polyfunctional monomer (PFM) to enhance the mechanical performance of PPC. When 8 wt% of PFM like triallyl isocyanurate (TAIC) was added, crosslinked PPC with a gel fraction of 60.7% was prepared at 50 kGy irradiation dose, which showed a tensile strength at 20 °C of 45.5 MPa, whereas it was only 38.5 MPa for pure PPC. The onset degradation temperature (T_i) and glass transition temperature (T_g) of this crosslinked PPC was 246 °C and 45 °C, respectively, a significant increase related to pure PPC of 211 °C and 36 °C. Therefore, thermal and mechanical performances of PPC could be improved via electron-beam irradiation in the presence of suitable PFM.     

Biodegradable poly(propylene carbonate)/layered double hydroxide composite films with enhanced gas barrier and mechanical properties

Relatively well crystallized and high aspect ratio Mg-Al layered double hydroxides(LDHs) were prepared by coprecipitation process in aqueous solution and further rehydrated to an organic modified LDH(OLDH) in the presence of surfactant. The intercalated structure and high aspect ratio of OLDH were verified by X-ray diffraction(XRD) and scanning electron microscopy(SEM). A series of poly(propylene carbonate)(PPC)/OLDH composite films with different contents of OLDH were prepared via a melt-blending method. Their cross section morphologies, gas barrier properties and tensile strength were investigated as a function of OLDH contents. SEM results show that OLDH platelets are well dispersed within the composites and oriented parallel to the composite sheet plane. The gas barrier properties and tensile strength are obviously enhanced upon the incorporation of OLDH. Particularly, PPC/2%OLDH film exhibits the best barrier properties among all the composite films. Compared with pure PPC, the oxygen permeability coefficient(OP) and water vapor permeability coefficient(WVP) is reduced by 54% and 17% respectively with 2% OLDH addition. Furthermore, the tensile strength of PPC/2%OLDH is 83% higher than that of pure PPC with only small lose of elongation at break. Therefore, PPC/OLDH composite films show great potential application in packaging materials due to its biodegradable properties, superior oxygen and moisture barrier characteristics.     

脂肪族聚碳酸酯(PPC)与聚乳酸(PLA)共混型生物降解材料的热学性能、力学性能和生物降解性研究

通过溶液浇铸法制备了脂肪族聚碳酸酯与聚乳酸的共混物(PPC/PLA).采用示差热分析(DSC)和热重分析(TG)研究了材料的热性能.采用拉伸力学试验研究了共混物的力学性能.通过土壤悬浊拟环境培养降解实验法和扫描电子显微镜分析(SEM)对共混材料的生物降解性能进行了研究.实验结果表明,随着PPC含量的增加,共混物的拉伸强度和杨氏模量降低,而生物降解速率却显著提高.但是,在一定的降解时间内,某些比例共混物的降解速率比100%PPC还要快.综合分析表明,PPC/PLA是力学性能和降解性能可以互补的共混体系.     

聚碳酸1,2-丙二酯/聚琥珀酸丁二酯/邻苯二甲酸二烯丙酯共混体系的研究

采用熔融共混的方法制备了聚碳酸1,2-丙二酯(PPC)/聚琥珀酸丁二酯(PBS)共混物和PPC/PBS/DAOP(邻苯二甲酸二烯丙酯)增塑共混物,对共混物的相容性、热性能、结晶性和物理机械性能进行了初步研究.研究结果表明PPC/PBS共混物为不相容体系,PPC对PBS的结晶度影响很小;PBS的加入提高了共混物的起始热分解温度(Td-5%),当共混物中PBS含量从10%增加到90%时,共混物的Td-5%可分别增加15℃到59℃.DAOP对PPC/PBS共混物有增塑作用,当PPC/PBS/DAOP的比例从30/70/0变化到30/70/30时,共混物玻璃化转变温度(Tg)下降了36.9℃.与PPC/PBS共混物相比,组成优化的DAOP增塑共混物PPC/PBS/DAOP(PPC/PBS/DAOP=30/70/5)的断裂伸长率和断裂能最大可提高31倍和34倍,分别达到655.1%和3.4 J/mm2,因此引入DAOP尽管使共混材料的热稳定性有所下降,但拓宽了PPC/PBS共混材料的使用温度窗口.     

Functionalized-graphene/ethylene vinyl acetate co-polymer composites for improved mechanical and thermal properties

The surface functionalization of graphene and the preparation of functionalized graphene/ethylene vinyl acetate co-polymer (EVA) composites by solution mixing are described. Octadecyl amine (ODA) was selected as a surface modifier for the preparation of functionalized graphene (ODA-G) in an aqueous medium. The ODA-G was characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, which confirm the modification and reduction of graphite oxide to graphene. Atomic force microscopy shows that the average thickness of ODA-G is ca. 1.9 nm. The ODA-G/EVA composites were characterized by X-ray diffraction and transmission electron microscopy, which confirms the formation of ODA-G/EVA composites. Measurement of tensile properties shows that the tensile strength of the composites (with 1 wt.% ODA-G loading) is ∼74% higher as compared to pure EVA. Dynamic mechanical analysis shows that the storage modulus of the composites is much higher than that of pure EVA. The thermal stability of the composite with 8 wt.% of ODA-G is ∼42 °C higher than that of pure EVA. The electrical resistivity has also decreased in the composites with 8 wt.% of ODA-G.     

Preparation and characterization of formaldehyde-modified black liquor lignin/poly (propylene carbonate) composites

In this paper, the black liquor lignin (BL) from pulp and paper industry was chemically modified using formaldehyde to adjust its aggregation structure and dispersion behavior. The properties of the formaldehyde-modified black liquor lignin (BLF) were measured by Fourier transform infrared spectroscopy, transmission electron microscopy, and differential scanning calorimetry. Results indicated that the BLF had better dispersion ability than BL. Therefore, the BLF as reinforcing fillers was incorporated into poly(propylene carbonate) (PPC) by melt compounding to prepare biodegradable BLF/PPC composites. The tensile properties, microstructure, thermal decomposition properties, and rheological properties of the BLF/PPC composites were investigated. Results showed that the performance of composites was depend on the dispersion of BLF. After adding a small amount of BLF into PPC, the tensile strength, tensile modulus, thermal stability, and processing stability of the composite were significantly improved.     

Low contents of graphite improving general properties of poly(vinylidene fluoride)

Studies on graphite flakes with a lateral size greater than 50 μm, having a large number of stacked collapse blocks, are neglected and replaced by graphene nanosheets or by powdered graphite, which can be obtained from graphite through chemical or physical exfoliation, as filler in polymer composites. Besides, the production of graphene nanosheets or the purification of powdered graphite uses a high concentration of strong and toxic acids that pollutes the environment. These processes are extremely time-consuming and generate an expensive product. Composites of poly(vinylidene fluoride) (PVDF) were prepared via extrusion with graphite flakes with up to 60 μm thick and 700 μm lateral size, in the range from 0.1 to 5% m/m. The quality of graphite flakes was analyzed by thermogravimetric analysis, x-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared spectroscopy, and scanning electron microscopy. The increase in the graphite content in the PVDF matrix improved thermal resistance while showed an increase in the degree of crystallinity up to 25% by XRD and 43% by differential scanning calorimetry, approximately. Although the graphite acted as a nucleating agent, the content of the PVDF beta phase did not change. In the composites with up to 2.0% of graphite, a significant increase in mechanical properties, 13% modulus, and 36% in the storage modulus, evaluated by thermodynamic-mechanical analysis and tensile tests. In the analyses of time-domain nuclear magnetic resonance and oscillatory rheology in parallel plates, it was noticed that the increase of mechanical properties is due to the reinforcing effect along with the lubricant protection of stacked graphene sheets, attenuating the stress and friction between the polymer chains. Therefore, even though graphite flakes are inexpensive, that filler without any treatment at low contents are capable of significantly improving the performance of PVDF. This work suggests that these composites could be employed in applications such as electrical insulator with less energy dissipation, and also in oil pipelines, specifically to replace PVDF-based terpolymers or mixtures thereof, and polyamide-11 in flexible risers as a barrier layer, improving their performance.     

Fabrication and properties of poly(propylene carbonate)/calcium carbonate composites

Composites of poly(propylene carbonate) (PPC) reinforced with micrometric and nanometric calcium carbonate particles were prepared via melt mixing followed by compression molding. The morphology and mechanical and thermal behaviors of the composites were investigated. Static tensile tests showed that the tensile strength, stiffness, and ductility of the composites tended to increase with increasing contents of micrometric calcium carbonate particles. This improvement in the tensile properties was attributed to good interfacial adhesion between the fillers and matrix, as evidenced by scanning electron microscopy examination. However, because of the agglomeration of calcium carbonate nanoparticles during blending, those composites with nanoparticles exhibited the lowest tensile strength. Thermogravimetric measurements revealed that the incorporation of calcium carbonate into PPC resulted in a slight improvement in its thermooxidative stability. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1806–1813, 2003     

Thermal conductive PS/graphite composites

Polystyrene (PS) was compounded with graphite that possesses high thermal conductivity and layer structures, and the PS/graphite thermal conductive nano‐composites were prepared. Thermal conductivity of PS improved remarkably in the presence of the graphite, and a much higher thermal conductivity of 1.95 W/m K can be achieved for the composite with 34 vol% of colloidal graphite. The Maxwell‐Eucken model and the Agari model were used to evaluate the thermal conductivity of the composites. For the purpose of improving the interfacial compatibility of PS/graphite, realizing the exfoliation and nano‐dispersion of graphite in the PS matrix, three intercalation methods, including rolling intercalation, solvent intercalation, and pan milling intercalation, were applied to prepare the composites, and the morphologies, thermal conductivities, and mechanical properties of the composites were investigated. It should be noted that the one prepared by pan milling intercalation not only had excellent thermal conductivity but also much higher mechanical properties, resulting from a high degree of layer exfoliation of the graphite, the formation of the chain structure agglomerates of the graphite, and the creation of more conductive paths under the strong shear stress of pan milling. Copyright © 2008 John Wiley & Sons, Ltd.     

Simultaneous Improvements of Thermal Stability and Mechanical Properties of Poly（propylene carbonate） via Incorporation of Environmental-friendly Polydopamine

Inspired by the photoprotection, radical scavenging of melanin together with versatile adhesive ability of mussel proteins, polydopamine（PDA） nanoparticles were successfully prepared and incorporated into environmentally friendly polymer, poly（propylene carbonate）（PPC） via solvent blending. The prepared composites exhibited excellent thermal stability in air and nitrogen atmosphere and extraordinary mechanical properties. The composites displayed eminent increase of temperature at 5% weight loss（T5%） by 30-100 K with 0.3 wt%-2.0 wt% loadings, meanwhile, the tensile strength and Young＇s modulus were significantly improved from 11.5 MPa and 553.7 MPa to 40.5 MPa and 2411.2 MPa, respectively. The kinetic calculation indicated that improvement of T5% is presumably derived from suppressing chain-end unzipping. The glass transition temperature（Tg） of the PPC/PDA composites increased by 8-10 K. This is probably due to hydrogen bonding interaction since the abundant proton donors along PDA chains would interact with proton acceptors like C = O and C―O―C in PPC which would cause restriction of segmental motion of PPC chains.     

Composites of poly(L‐lactide‐trimethylene carbonate‐glycolide) and surface modified SBA‐15 as bone repair material

This work aims to develop novel composites from a poly(L ‐lactide‐co‐trimethylene carbonate‐co‐glycolide) (PLTG) terpolymer and mesoporous silica (SBA‐15) nanofillers surface modified by post‐synthetic functionalization. SBA‐15 first reacts with a silane coupling agent, γ‐aminopropyl‐trimethoxysilane to introduce ammonium group. PLLA chains were then grafted on the surface of SBA‐15 through ammonium initiated ring‐opening polymerization of L ‐lactide. Composites were prepared via solution mixing of PLTG terpolymer and surface modified SBA‐15. The structures and properties of pure SBA‐15, γ‐aminopropyl‐trimethoxysilane modified SBA‐15 (H₂N‐SBA‐15), PLLA modified SBA‐15 (PLLA‐NH‐SBA‐15), and PLTG/PLLA‐NH‐SBA‐15 composites were characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, transmission electron microscopy, N₂ adsorption‐desorption, differential scanning calorimetry, contact angle measurement, and mechanical testing. The results demonstrated that PLLA chains were successfully grafted onto the surface of SBA‐15 with grafting amounts up to 16 wt.%. The PLTG/PLLA‐NH‐SBA‐15 composites exhibit good mechanical properties. The tensile strength, Young's modulus, and elongation at break of the composite containing 5 wt.% of PLLA‐NH‐SBA‐15 were 39.9 MPa, 1.3 GPa, and 273.6%, respectively, which were all higher than those of neat PLTG or of the composite containing 5 wt.% of pure SBA‐15. Cytocompatibility tests showed that the composites present very low cytotoxicity.     

Completely biodegradable composites of poly(propylene carbonate) and short,lignocellulose fiber Hildegardia populifolia

The composites of biodegradable poly(propylene carbonate) (PPC) reinforced with short Hildegardia populifolia natural fiber were prepared by melt mixing followed by compression molding. The mechanical properties, thermal properties, and morphologies of the composites were studied via static and dynamic mechanical measurements, thermogravimetric analysis, and scanning electron microscopy (SEM) techniques, respectively. Static tensile tests showed that the stiffness and tensile strength of the composites increased with an increasing fiber content. However, the elongation at break and the energy to break decreased dramatically with the addition of short fiber. The relationship between the experimental results and the compatibility or interaction between the PPC matrix and fiber was correlated. SEM observations indicated good interfacial contact between the short fiber and PPC matrix. Thermogravimetric analysis revealed that the introduction of short Hildegardia populifolia fiber led to a slightly improved thermooxidative stability of PPC. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 666–675, 2004     

Thermal,mechanical and electroactive shape memory properties of polyurethane (PU)/poly (lactic acid) (PLA)/CNT nanocomposites

Polymer blend nanocomposites based on thermoplastic polyurethane (PU) elastomer, polylactide (PLA) and surface modified carbon nanotubes were prepared via simple melt mixing process and investigated for its mechanical, dynamic mechanical and electroactive shape memory properties. Chemical and structural characterization of the polymer blend nanocomposites were investigated by Fourier Transform infrared (FT-IR) and wide angle X-ray diffraction (WAXD). Loading of the surface modified carbon nanotube in the PU/PLA polymer blends resulted in the significant improvement on the mechanical properties such as tensile strength, when compared to the pure and pristine CNT loaded polymer blends. Dynamic mechanical analysis showed that the glass transition temperature (T_g) of the PU/PLA blend slightly increases on loading of pristine CNT and this effect is more pronounced on loading surface modified CNTs. Thermal and electrical properties of the polymer blend composites increases significantly on loading pristine or surface modified CNTs. Finally, shape memory studies of the PU/PLA/modified CNT composites exhibit a remarkable recoverability of its shape at lower applied dc voltages, when compared to pure or pristine CNT loaded system.     

Property correlations for composites based on ethylene propylene diene rubber reinforced with flax fibers

EPDM composites filled with short flax fibers were prepared by melt blending procedure. The effects of fiber loading on the mechanical, thermal and water uptake characteristics were studied. The physico-mechanical, morphological thermal properties and water absorption behavior were discussed using tensile testing, differential scanning calorimetry, thermogravimetrical analysis and scanning electron microscopy. Scanning electron microscopy revealed that the flax fibers were well dispersed in the polymer matrix. The tensile strength and hardness of the composites were found to be improved at higher fiber loading. The water absorption pattern of EPDM/fiber composites at room temperature follows a Fickian behavior for composites with 10, 15 and 20 phr flax fiber.     

Improved polyvinylpyrrolidone (PVP)/graphite nanocomposites by solution compounding and spray drying

In order to evaluate the roles of graphite dispersion on the functional properties of the composites, PVP/graphite nanocomposites were prepared by blending the aqueous suspension of expanded graphite sheets and polyvinylpyrrolidone (PVP) aqueous solution by ultrasonic treatment, followed by spray drying and direct drying as a comparison individually. The effects of graphite loading and drying method on the dispersion of graphite and the resultant properties of the composites such as electrical and thermal conductivity, friction, and dynamic mechanical properties were studied. The results from transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X‐ray diffraction showed that the composites prepared by fast spray drying exhibited a higher degree of exfoliation and a better dispersion of graphite sheets in the PVP matrix than the corresponding composites prepared by direct drying, leading to a conclusion that fast spray drying can effectively prevent from re‐stacking of the exfoliated graphite sheets as illustrated. As a result, dynamic mechanical thermal analysis showed significant increases in the storage modulus and glass transition temperature for the composites prepared by spray drying. Besides, the spray drying as well greatly improved the electrical and thermal conductivity of the composites. It was also found that the electrical and thermal conductivity of the composites strongly depended on the graphite dispersion, while the friction coefficient unexpectedly does not. Increasing graphite loading level might enhance the probability of graphite sheets re‐stacking, resulting in poor graphite dispersion. Copyright © 2011 John Wiley & Sons, Ltd.     

Fabrication of thermoplastic polyurethane composites with a high dielectric constant and thermal conductivity using a hybrid filler of CNT@BaTiO3

Thermoplastic polyurethane composites with an excellent dielectric constant and high thermal conductivity were obtained using CNT@BaTiO₃ as a filler through a low-speed melt extrusion method. Before preparing the hybrid filler for the composite, the filler particles were surface modified to ensure that the outer surfaces could facilitate the reaction among particles to form the hybrid and ensure complete dispersion in the thermoplastic polyurethane matrix. After confirming the proper surface treatment of the filler particles using infrared spectroscopy, thermal degradation analysis and field emission scanning electron microscopy, they were used to prepare the composite materials at a processing temperature of 200 °C. The thermal stability, thermomechanical properties, mechanical properties, thermal conductivity, and dielectric properties of the composites were investigated. Compared to the neat thermoplastic polyurethane matrix, the prepared composite exhibited a higher thermal stability, approximately 300% higher storage modulus, higher tensile strength and elongation at break values, approximately three times higher thermal conductivity (improved from 0.19 W/(m.K) to 0.38 W/(m.K), and approximately five times larger dielectric constant at high frequencies (at 1 MHz a dielectric constant of 19.2 was obtained).     

Biodegradable polyester/modified mesoporous silica composites for effective bone repair with self‐reinforced properties

A series novel composites based on poly(_L‐lactide) (PLLA) oligomer modified mesoporous silica (MCM41) homogeneous dispersed into poly(_L‐lactide‐co‐trimethylene carbonate‐co‐glycolide) (PLTG) terpolymer has been successfully prepared. The structure of PLTG terpolymer was characterized by ¹H NMR. The structure and properties of modified and unmodified MCM41 were attested by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analyzer (TGA), X‐ray diffraction (XRD), N₂ adsorption–desorption, scanning electron microscope (SEM), and transmission electron microscope (TEM), which demonstrated that the MCM41 was successfully grafted by the PLLA oligomer. The effect of different concentration of modified MCM41 in PLTG matrix on thermal properties, mechanical properties, and hydrophilicity was investigated by TGA, differential scanning calorimetry (DSC), mechanical testing, contact angle measurement, and SEM. The results of mechanical tests showed that 5 wt% of modified MCM41 nanoparticles gave rise to optimal reinforcing effect. The tensile strength, Young's modulus, and elongation at break of the PLTG/PLLA‐MCM41 (5%) composites were 33.2 Mpa, 1.58 Gpa, and 268.7%, respectively, which were all higher than the PLTG/MCM41 (5%) composites and pristine PLTG matrix, which were due to good interfacial adhesion between the PLTG matrix and MCM41 nanoparticles. TGA and DSC have shown that 5% modified MCM41 in the PLTG increased the temperature of composite degradation and T_g. Water contact angle measurement showed the hydrophilicity of the composites increases with the increase of modified MCM41 content. The live/dead assay showed that the modified MCM41 existing on the PLTG matrix presents very excellent cytocompatibility. Therefore, the novel composite material represents promising way for bone tissue engineering application.