Thermal properties of phosphorylated nanodiamond reinforced polyimides

Recently, the preparation of nanodiamond–polymer composites has attracted the attention of materials scientists due to the unique properties of nanodiamonds. In this study, novel polyimide (PI)/phosphorylated nanodiamonds (PNDs) composites were prepared. PNDs were achieved from the reaction of methylphosphonic dichloride with nanodiamonds in dichloromethane. Precursor of polyimide, which is the poly(amic acid) (PAA), was successfully synthesized with 3,3′, 4,4′‐benzophenonetetracarboxylic dianhydride and 4,4′‐oxydianiline in the solution of N,N‐dimethylformamide. Different ratios of phosphorylated nanodiamond particles were added into PAA solution and four different nanocomposite films were prepared. The amount of PNDs in the composite films was varied from 0 wt% to 3 wt%. The structure, thermal and surface properties of polyimide films were characterized by scanning electron microscopy (SEM), ATR‐FTIR, thermogravimetric analysis (TGA), ultraviolet visible spectroscopy, and contact angle. SEM and FTIR results showed that the phosphorylated nanodiamond and PI/PNDs films were successfully prepared. Phosphorylated nanodiamonds were homogeneously dispersed in the polymer matrix and they displayed good compatibility. TGA results showed that the thermo‐oxidative stability of PI/PNDs films was increased with the increasing amount of phosphorylated nanodiamond. POLYM. COMPOS., 37:2285–2292, 2016. © 2015 Society of Plastics Engineers     

Oxidative graft polymerization of aniline on the modified surface of polypropylene films

A novel method for preparing electrically conductive polypropylene‐graft‐polyacrylic acid/polyaniline (PP‐g‐PAA/PANI) composite films was developed. 1,4‐Phenylenediamine (PDA) was introduced on the surface of PP‐g‐PAA film, and then, chemical oxidative polymerization of aniline on PP‐g‐PAA/PDA film was carried out to prepare PP‐g‐PAA/PANI electrically conductive composite films. After each step of reaction, the PP film surface was characterized by attenuated total reflectance Fourier transform infrared spectroscopy. Static water contact angles of the PP, PP‐g‐PAA, and PP‐g‐PAA/PANI films were measured, and the results revealed that graft reactions took place as expected. The morphology of the PP‐g‐PAA film and the PP‐g‐PAA/PANI composite film were observed by atomic force microscopy. The conductivity and the thickness of the PP‐g‐PAA/PANI composite films with 1.5 wt % PANI were around 0.21 S/cm and 0.4 μm, respectively. The PANI on the PP‐g‐PAA/PANI film was reactivated and chain growing occurred to further improve the molecular weight of PANI. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2442–2450, 2007     

Effect of glycerin on structure transition of PVA/SF blends

Blend films of silk fibrion (SF) and poly(vinyl alcohol) (PVA), with glycerin as an additive, were made, and the structure and properties of the blends were investigated by scanning electron microscopy (SEM), Fourier transform infrared (FT‐IR) spectroscopy, differential scanning calorimetry (DSC), and wide‐angle X‐ray diffraction (WAXD) and with an Instron Material Tester. The results showed that SF and PVA are principally incompatible and the blends made by the two polymers were phase‐separated. The results, however, also demonstrated that the blend structure could be changed to some extent by addition of 3–8% glycerin. The boundary of the PVA and SF phases became indistinct, as reported by SEM, a new peak appeared in the WAXD curves, the width of the OH absorption peak in the FT‐IR spectra increased, and the melting points changed in the DSC curves. In particular, the mechanical properties obviously increased, from 350 kg/cm² and 10% of PVA/SF (80/20) film to 832 kg/cm² and 39% of PVA/SF (80/20) film because of the increase in glycerin. It was suggested that glycerin plays a role in building the relationship between PVA and SF, strengthening the interaction between them and improving their compatibility. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2342–2347, 2002     

Polyester/natural fiber biocomposites: preparation,characterization, and biodegradability

In this study, the biodegradability, morphology, mechanical, and thermal properties of composite materials composed of polybutyleneterephthalate (PBT), acrylic acid-grafted PBT (PBT-g-AA), and sisal fibers (SFs) were evaluated. Composites containing acrylic acid-grafted PBT (PBT-g-AA/SF) exhibited superior mechanical properties because of their greater compatibility with SF than PBT/SF. The dispersion of SF in the PBT-g-AA matrix was highly homogeneous due to ester formation and the creation of branched and cross-linked macromolecules between the carboxyl groups of PBT-g-AA and the hydroxyl groups of SF. Furthermore, due to its lower melting temperature (T _m), the PBT-g-AA/SF composite was more readily synthesized. Each composite was subjected to biodegradation tests in a soil environment. Both the PBT and PBT-g-AA/SF composite films were completely degraded, with severe disruption of the film structures observed after 60–100 days of incubation. Although the degree of weight loss following burial indicated that both materials were biodegradable, even with high levels of SF loading, the higher water resistance of PBT-g-AA/SF films indicated their higher biodegradability than the PBT films.     

Phase study of nylon 6/poly (acrylic acid) blends cast from solutions in aqueous formic acid

Blends of nylon 6 (Ny6) with poly(acrylic acid) (PAA) were prepared in film form from solutions in a mixture of formic acid and water by evaporating the solvent. The miscibility and phase constitution of the binary blends obtained over a wide composition range (5/95–95/5) were examined by wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and dynamic mechanical measurements. A Ny6 homopolymer film and Ny6/PAA blends with PAA concentrations ≥ 50 wt% exhibited a WAXD profile stemmed from the coexistence of two different crystalline modifications of Ny6, i.e. the α and γ forms. Above 50 wt% PAA content, the solution-cast blends showed no definite crystallinity. It was found by DSC thermal analysis that the polymer pair is substantially miscible in the non-crystalline state, since a single glass transition temperature (T_g) was situated between the T_gs of the two homopolymers at every composition; however, the T_g versus composition plots did not follow a monotonic function but yielded a peak maximum at a PAA concentration of c. 25 wt%. In order to interpret this phenomenon, attention was given to the following point revealed by dynamic mechanical measurements: at the compositions of Ny6/PAA = 100/0–50/50, a phase of low regularity such as a nematic structure is formed in the cast films.     

Preparation,characterization, and biodegradability of renewable resource‐based composites from recycled polylactide bioplastic and sisal fibers

The biodegradability, morphology, and mechanical thermal properties of composite materials composed of polylactide (PLA) and sisal fibers (SFs) were evaluated. Composites containing acrylic acid‐grafted PLA (PLA‐g‐AA/SF) exhibited noticeably superior mechanical properties because of greater compatibility between the two components. The dispersion of SF in the PLA‐g‐AA matrix was highly homogeneous as a result of ester formation and the consequent creation of branched and crosslinked macromolecules between the carboxyl groups of PLA‐g‐AA and hydroxyl groups in SF. Furthermore, with a lower melt temperature, the PLA‐g‐AA/SF composite is more readily processed than PLA/SF. Both composites were buried in soil to assess biodegradability. Both the PLA and the PLA‐g‐AA/SF composite films were eventually completely degraded, and severe disruption of film structure was observed after 6–10 weeks of incubation. Although the degree of weight loss after burial indicated that both materials were biodegradable even with high levels of SF, the higher water resistance of PLA‐g‐AA/SF films indicates that they were more biodegradable than those made of PLA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Development and compatibility assessment of new composite film based on sugar beet pulp and polyvinyl alcohol intended for packaging applications

In this study, interaction and compatibility between sugar‐beet pulp (SBP) and polyvinyl alcohol (PVA) in blend films was assessed. Film‐forming dispersions of different ratios of SBP to PVA (100/0, 75/25, 50/50, and 25/75) were cast at room temperature. The effects of adding PVA to SBP on the resulting film's physical, mechanical and barrier properties and thermal stability were investigated. X‐ray diffraction and environmental scanning electron microscopy (ESEM) were used to characterize the structure and morphology of the composites. When PVA was also added to the composite films, the films became softer, less rigid and more stretchable than pure SBP films. The addition of PVA gave significantly greater elongation at break (12.45%) and lower water vapor permeability (1.55 × 10^?10 g s^?1 m^?1 Pa^?1), but tensile strength did not markedly change, remaining around 59.68 MPa. Thermogravimetric analysis also showed that SBP/PVA film had better thermal stability than SBP film. The ESEM results showed that the compatibility of SBP50/PVA50 was better than those of other composite films. These results suggest that when taking all the studied variables into account, composite films formulated with 50% PVA are most suitable for various packaging applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41354.     

丝素蛋白/聚丙烯酸共混膜仿生合成羟基磷灰石

将丝素蛋白(SF)与聚丙烯酸(PAA)共混,制备丝素蛋白/聚丙烯酸(SF/PAA)共混膜;然后将此共混膜进行改性及矿化处理后,放置于(37±0.5)℃人体仿生液中24h,诱导合成丝素蛋白/羟基磷灰石(SF/HA)复合材料.利用傅里叶红外(FTIR)、X-射线衍射(XRD)、环境扫描电镜(ESEM)以及X射线能谱(EDX...     

Synthesis of high-performance composites by in situ polycondensation and their mechanical properties

High-performance composites of vinylpyridine-styrene copolymers and polyamic acid (PAA) were prepared by the so-called ‘in situ polymerization method’. Poly(4-vinylpyridine-co-styrene) (P4VPy-St) and poly(2-vinyl pyridine-co-styrene) (P2VPy-St) were used as flexible matrix polymers. A molecular composite could be obtained from a polymer pair having an attractive interaction such as a coulombic interaction. Their morphologies were observed by scanning electron microscopy (SEM); mechanical properties of these composites were studied by tensile tests. The PAA content dependence of tensile strength for the composite films obtained by the in situ polymerization method was investigated. The tensile strength of the resulting composite was about 1.5 times higher than that of PAA film. The coulombic interaction between the pyridine moiety in the matrix copolymer and resulting PAA enhanced both the miscibility and mechanical properties of the composites. Furthermore, a polyimide (PI) structure was formed by stepwise heat-treatment and greatly enhanced the tensile strength of the composite films.     

Preparation and characterization of biomimetic silk fibroin/chitosan composite nanofibers by electrospinning for osteoblasts culture

ABSTRACT: In this study, we have successfully fabricated electrospun bead-free silk fibroin [SF]/chitosan [CS] composite nanofibers [NFs] covering the whole range of CS content (0%, 25%, 50%, 75%, and 100%). SF/CS spinning solutions were prepared in a mixed solvent system of trifluoroacetic acid [TFA] and dichloromethane. The morphology of the NFs was observed by scanning electron microscope, and the average fiber diameter ranges from 215 to 478 nm. Confocal laser scanning microscopy confirms the uniform distribution of SF and CS within the composite NFs. To increase biocompatibility and preserve nanostructure when seeded with cells in culture medium, NFs were treated with an ethanol/ammonia aqueous solution to remove residual TFA and to change SF protein conformation. After the chemical treatment, SF/CS NFs could maintain the original structure for up to 54 days in culture medium. Properties of pristine and chemically treated SF/CS NFs were investigated by Fourier transform infrared spectroscopy [FT-IR], X-ray diffraction [XRD], and thermogravimetry/differential scanning calorimetry [TG/DSC]. Shift of absorption peaks in FT-IR spectra confirms the conformation change of SF from random coil to β-sheet by the action of ethanol, which is also consistent with the SF crystalline diffraction patterns measured by XRD. From TG/DSC analysis, the decomposition temperature peaks due to salt formation from TFA and protonated amines disappeared after chemical treatment, indicating complete removal of TFA by binding with ammonium ions during the treatment. This was also confirmed with the disappearance of F1s peak in X-ray photoelectron spectroscopy spectra and disappearance of TFA salt peaks in FT-IR spectra. The composite NFs could support the growth and osteogenic differentiation of human fetal osteoblastic [hFOB] cells, but each component in the composite NF shows distinct effect on cell behavior. SF promotes hFOB proliferation while CS enhances hFOB differentiation. The composite SF/CS NFs will be suitable for bone tissue engineering applications by choosing a suitable blend composition.PACS: 87.85.jf; 87.85.Rs; 68.37.Hk.     

Synthesis of processible doped polyaniline‐polyacrylic acid composites

Processible composites of emeraldine salt form of polyaniline (PANI) with polyacrylic acid (PAA) are synthesized and studied for their structural, electrical, mechanical, thermal, and electrochemical properties. The processible conducting composites of various weight percentage from 20 wt % to 90 wt % (of PANI) have been prepared by mixing the PANI and PAA under vigorous stirring and sonication conditions. Self‐standing films of electroactive homogeneous composites are obtained by solution casting method. A significant improvement in processibility, crystallinity, and thermal stability is observed in the composites; however, the electrical conductivity decreased remarkably as the percentage of PANI is decreased in the composites. The 60 wt % PANI‐PAA composite showed crystalline structural property with orthorhombic crystal system and cell parameters as a = 5.93Å, b = 7.57Å, and c = 10.11Å. The 60 wt % PANI‐PAA composite also showed better thermal stability and highest capacitance amongst all the composites and used as an active material for development of electrochemical capacitors (parallel plate assembly). The processible composites based electrochemical capacitors using 0.5 M NaClO₄‐Acetonitril electrolyte showed super capacitance with ease in fabrication and cost effectiveness in comparison to other similar materials based capacitors. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

莲藕淀粉/乳清蛋白复合膜的制备、表征及性能

将莲藕淀粉与乳清蛋白按1∶0.3、1∶0.4、1∶0.5、1∶0.6、1∶0的质量比共混得到系列复合膜，探究不同比例乳清蛋白的添加对膜性能的影响。通过SEM、XRD、FTIR、DSC及TG对复合膜进行表征，在常温环境下对复合膜的机械性能和阻隔性能进行测定。结果表明，乳清蛋白的添加对膜的机械性能、阻隔性能均有所改善，特别当莲藕淀粉∶乳清蛋白=1∶0.5时，成膜基质间相互作用，紧密结合，相容性良好，且机械性能及阻隔性能最佳，抗拉强度和断裂伸长率分别达到11.66 MPa和14.71 %，热稳定性好。     

Properties of Silk Fibroin/Poly(vinyl alcohol) Blend Solutions and Peculiar Structure Found in Heterogeneous Blend Films*

The gelation of aqueous poly(vinyl alcohol) (PVA) solution was accelerated by addition of a small amount of silk fibroin (SF). The peculiar structure found in heterogeneous SF/PVA blend films was analysed by polarizing microcopy, differential scanning calorimetry (DSC), infrared spectroscopy (IR), and scanning electron microscopy (SEM). The blend films (over 30μm thick) of SF/PVA (90/10 to 60/40 weight ratio) separated macroscopically into two phases: SF-rich and PVA-rich. SF-rich phases had many spherical particles (1–25μm). In the PVA-rich phases, a fabric-like plain weave structure was found microscopically under a dark field. The SF-rich and PVA-rich phases were analysed by DSC, IR and SEM. The phase separation is also discussed. © of SCI.     

Synthesis and properties of polyimides from 1,3-bis(4-piperidino-l,S-naphthalic anhydride)propane

Summary A novel dianhydride containing nathphalene units was prepared by Ullmann reaction of 4-bromo-1,8-nathphalic anhydride with trimethylenedipiperidine and polymerized with various aromatic diamines in one-pot polycondensation at high temperature in m-cresol. All the polyimides are soluble in organic solvents and form transparent yellow thin films by solution casting. Their inherent viscosities were ranged in 0.17 - 0.68 dL /g (in m-cresol at 25□). The glass transition temperatures were from 202.7□ to 263.6□ by DSC. These polymers did not show appreciable decomposition up to 380□ in N₂ by TGA and can emit strong green fluorescence in solution and in solid state. They may be potential light emitting and solar energy conversion materials. Received: 26 September 2002/Revised version: 6 January 2003/ Accepted: 10 January 2003 Correspondence to Deyue Yan     

Mechanical properties of silk fibroin–microcrystalline cellulose composite films

Silk fibroin–microcrystalline cellulose (cellulose whisker) composite films with varied compositions were prepared by casting mixed aqueous solution/suspensions of the two components. Silk fibroin was dissolved in 10M LiSCN followed by dialysis; a cellulose whisker suspension was prepared by sulfuric acid hydrolysis of tunicate cellulose. Macroscopically homogeneous films were obtained at all mixing ratios. While the Young's modulus of the composite films showed a linear, additive dependence on the mixing ratio, the tensile strength and ultimate strain showed a maximum at a 70–80% cellulose content, reaching five times those of fibroin‐alone or cellulose‐alone films. At the same mixing ratio, infrared spectra of the composite films showed a shift of the amide I peak from 1654 to 1625 cm^?1, indicating the conformational change of fibroin from a random coil to a β structure (silk II) at the whisker–matrix interface. This change seems to be induced by contact of fibroin molecules with a highly ordered surface of cellulose whisker. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3425–3429, 2002     

PAA/PEG复合水凝胶膜的制备及其性能

以丙烯酸(AA)为单体、聚乙二醇(PEG)为大分子模板、N,N-亚甲基双丙烯酰胺为交联剂、过硫酸铵为引发剂,通过自由基溶液聚合法原位聚合制备了聚丙烯酸(PAA)/PEG复合水凝胶膜,研究了PEG用量对复合水凝胶成膜性、热稳定性、溶胀性能和力学性能的影响。结果表明:成功制备了PAA/PEG复合水凝胶膜;适量PEG的引入有利于复合水凝胶成膜;PAA/PEG复合水凝胶膜的热稳定性良好;PEG的引入对水凝胶膜的吸水溶胀性能不利;适量PEG有利于提高凝胶的力学性能,复合水凝胶膜软而韧;PEG与AA质量比为0.4的PAA/PEG复合水凝胶的拉伸强度和断裂标称应变最大,分别为1.58 MPa,414%。     

Study on secondary structural transition of nano‐TiO2 modified silk fibroin composite films by two‐dimensional Raman correlation spectroscopy and solid‐state 13C‐NMR spectroscopy

By a sol–gel processing, the nano‐TiO₂/silk fibroin (SF) composite films were prepared. One‐dimensional (1D) Raman, two‐dimensional (2D) correlation Raman spectroscopy, and ¹³C cross‐polarization magic‐angle‐spinning nuclear magnetic resonance (¹³C CP‐MAS NMR) were used to characterize the structural evolution of SF as the nano‐TiO₂ content increased from 0 to 0.4 wt%. The experimental data demonstrated that the secondary structures in the pure SF film and nano‐TiO₂/silk fibroin (SF) composite films were random coil, α‐helix and β‐sheet structures. The nano‐TiO₂ particles formed in the SF films might induce partial structural transitions from random coil and Silk I (α‐helix) to Silk II (β‐sheet). The transition identified by 2D‐Raman correlation spectra was the following order: silk I‐like structure, silk I (α‐helical structure), Silk II‐like structure, and Silk II (β‐sheet structure). POLYM. COMPOS., 36:121–127, 2015. © 2014 Society of Plastics Engineers     

Mechanical properties of nanocomposites from sorbitol plasticized starch and tunicin whiskers

Nanocomposite materials were obtained using sorbitol plasticized waxy maize starch as matrix and tunicin whiskers as the reinforcement. The effect of filler load (0–25 wt % whiskers) and the relative humidity levels (0–98%) on the mechanical behavior of the films are discussed for linear and nonlinear deformation. The performance of the films is explained, based on the morphology and structural behavior of the composite materials (Mathew and Dufresne, Biomacromolecules 2002, 3, 609). The nanocomposites exhibit good mechanical strength due to the strong interaction between tunicin whiskers, matrix, plasticizer (sorbitol), and water, and due to the ability of the cellulose filler to form a rigid three‐dimensional network. The evolution of T_g as a function of relative humidity level and filler load is studied in detail. A decrease in crystallinity of the amylopectin phase is observed at high filler loads, due to the resistance to chain rearrangement imposed by the whiskers. The mechanical strength increased proportionally with filler loads, showing an effective stress transfer from the matrix to the whiskers. An even distribution of whiskers (as determined by SEM) and plasticizer in the matrix contributes to the mechanical performance. The mechanical properties of the nanocomposites showed a strong dependence on relative humidity conditions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Sorption/release of diclofenac sodium in/from free‐standing poly(acrylic acid)/poly(ethyleneimine) multilayer films

Polyelectrolyte multilayer films deposited onto various substrates have been used extensively as drug delivery systems. However, little attention has been paid to the release of drugs from free‐standing polymeric films. Herein, we report the construction of thermal crosslinked free‐standing poly(acrylic acid) (PAA)/branched poly(ethyleneimine) (PEI) multilayer films composed of 25 double layers [(PAA/PEI)₂₅] and their use in sorption/release of diclofenac sodium (DS). The (PAA/PEI)₂₅ multilayer films were characterized by scanning electron microscopy, potentiometric titrations and Fourier transform infrared spectroscopy, while the sorption/release of DS was monitored by UV – Vis spectroscopy. The DS sorption equilibrium data were fitted with five isotherm models (Langmuir, Freundlich, Sips, Dubinin–Radushkevich, and Temkin). The maximum equilibrium sorption capacity, q_m, given by the Langmuir model was 32.42 mg DS/g. The Korsmeyer–Peppas semiempirical equation showed that the release of DS from the free‐standing (PAA/PEI)₂₅ films proceeded by pseudo‐Fickian diffusion, irrespective of the releasing media. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43752.     

Study on molecular interaction behavior,and thermal and mechanical properties of polyacrylic acid and lactose blends

Polyacrylic acid (PAA) blending with lactose or polyol, a lactose derivative, is investigated by Fourier transform infrared, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and stress–strain tests. The IR spectra of PAA/lactose blends exist shifting around 1700 cm and 3400 cm^?1, implying intermolecular hydrogen‐bonding interaction between two compounds. DSC data show that PAA and lactose are miscible below 17% lactose. At the higher content of lactose, phase separation occurs due to lactose self‐association. Comparing to PAA/lactose blends, PAA/ polyol systems show much weaker hydrogen‐bonding interaction effect. All blending systems studied exhibit extensive reduction in their thermal and mechanical properties. The result suggests that both lactose and polyol cannot be used as effective additives to enhance the physical properties of PAA. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1921–1927, 2001