Effect of sepiolite nanoparticles on the properties of novel poly(sulfone ether imide)

A new poly(sulfone ether imide) was prepared, and related nanocomposites were produced through introduction of sepiolite nanoparticles into the matrix of polymer. Inherent viscosity, thermal and mechanical features of pristine poly(sulfone ether imide), and nanocomposite samples were evaluated and compared. The crystallinity was also investigated. Dispersion and distribution behaviors of nanocomposite samples and cross‐sectional morphology of nanocomposite films were also studied. Also, the optimized amounts of sepiolite nanoparticles in the matrix of polymer were determined by microscopic techniques (scanning electron microscope and transmission electron microscope). By introduction of 3 wt% of sepiolite, superior thermal and mechanical properties were observed. Copyright © 2016 John Wiley & Sons, Ltd.     

Alignment effect of attapulgite on the mechanical properties of poly(vinyl alcohol)/attapulgite nanocomposite fibers

Poly(vinyl alcohol) (PVA)/attapulgite (AT) nanocomposite fibers have been prepared by wet spinning. The morphology and mechanical properties of the modified PVA fibers have been characterized with transmission electron microscopy, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), birefringence measurements, and mechanical testing. The PVA/AT nanocomposite fibers show much higher tensile strength, initial modulus, and work to break than pure PVA fibers with the same draw ratio. SEM observations demonstrate that the AT nanorods can align orderly along the fiber axis by stretching and have good adhesion to the fiber matrix. The results of birefringence measurements prove that the modified fibers have higher orientation than pure PVA fibers after stretching. The results of DSC analysis indicate that the crystallinity of the PVA fibers can be increased by the addition of AT. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1995–2000, 2006     

Investigating properties of poly (ether‐amide)/MWCNT nanocomposite films containing 2,7‐bis(4‐aminophenoxy)naphthalene and isophthalic segments

Three nanocomposite films based on aramid (poly (ether‐amide), PEA) and multiwall carbon nanotubes (MWCNT) were prepared via solution casting method using 2,7‐bis(4‐aminophenoxy)naphthalene (4) and isophthalic acid (5) containing various amounts of MWCNT (2, 3, 5 wt.%). To comprehensively analyze the properties of the cast films as well as the monomers, different techniques were employed, namely FT‐IR, ¹H NMR, X‐ray diffraction, and field emission scanning electron microscopy. Also, thermal and tensile properties of PEA (6) and nanocomposite films were investigated using thermogravimetric analysis and mechanical analysis, respectively. The morphology, thermal, and mechanical properties of nanocomposite films approved that MWCNT had well dispersion in the PEA matrix and showed a synergistic effect on improving all of the investigated properties. Based on the thermogravimetric analysis results, employing MWCNT caused to increase in the char yields from 61 (in the neat PEA) to 66 (in the PEA /MWCNT nanocomposite 5 wt.%) under the nitrogen atmosphere. In comparison to the pristine PEA (426°C), the temperature at 10 losses mass % (T₁₀) was increased from 530°C to 576°C, with 2 to 5 wt.% of MWCNT. Mechanical analysis revealed that the tensile strength and initial modulus were improved by incorporating MWCNT into PEA (81.70–93.40 MPa and 2.10–2.22 GPa, respectively). Electrical conductivity of the PEA/MWCNT nanocomposites was displayed maximum value in the 5 wt.%, showing satisfactory value in many application areas. The X‐ray diffraction technique was employed to study the crystalline structure of the prepared nanocomposite films as well as PEA. In addition, the electrochemical impedance spectroscopy study demonstrated that the prepared nanocomposites had significant impedance improvement in the presence of MWCNTs.     

Poly(lactic acid)/(styrene‐ethylene‐butylene‐styrene)‐g‐maleic anhydride copolymer/sepiolite nanocomposites: Investigation of thermo‐mechanical and morphological properties

In this study, sepiolite nanoclay is used as reinforcing agent for poly(lactic acid) (PLA)/(styrene‐ethylene‐butylene‐styrene)‐g‐maleic anhydride copolymer (SEBS‐g‐MA) 90/10 (w/w) blend. Effects of sepiolite on thermal behavior, morphology, and thermomechanical properties of PLA/SEBS‐g‐MA blend were investigated. Differential scanning calorimetry results showed 7% improvement in crystallinity at 0.5 wt% of sepiolite. The nanocomposite exhibited approximately 36% increase in the tensile modulus and 17% increase in toughness as compared with the blend matrix at 0.5 and 2.5 wt% of sepiolite respectively. Field emission scanning electron microscopy and transmission electron microscopy images exhibited sepiolite‐induced morphological changes and dispersion of sepiolite in both PLA and SEBS‐g‐MA phases. Dynamic mechanical analysis and wide angle X‐ray diffraction present evidences in support of the reinforcing nature of sepiolite and phase interaction between the filler and the matrix. This study confirms that sepiolite can improve tensile modulus and toughness of PLA/SEBS‐g‐MA blend.     

Microstructure and free volume evaluation of poly(vinyl alcohol) nanocomposite hydrogels

A new type of organic/inorganic nanocomposite hydrogel was prepared by introducing small amount of natural montmorillonite (MOM) into a poly(vinyl alcohol) (PVA)/sulfonated polyester (PES) system. The crystalline structure and crystallinity degree were determined by differential scanning calorimetry (DSC) and wide angle X-ray spectroscopy (WAXS). The presence of PES leads to an increase in the crystallinity degree of the PVA matrix and a significant decrease in the melting temperature. The addition of small amount of clay (1-5%) resulted in an increase of the average crystallite dimension, crystallinity degree and melting temperature, as compared to the PVA/PES system. The presence of the clay resulted in a substantial increase on the free volume size, as suggesting by positron annihilation lifetime spectroscopy (PALS). This result suggests a lower packing efficiency of the PVA chain and the formation of a PVA-MOM interfacial layer. This interfacial layer and the increasing of the mobility of the PVA chain by the presence of the clay reflects also in a decrease of the glass transition temperature, determined by dynamic mechanical analysis.     

Fabrication and characterization of poly(vinyl alcohol)/chitosan hydrogel thin films via UV irradiation

A series of poly(vinyl alcohol)/chitosan (PVA/CTS) hydrogel thin films were prepared via ultraviolet (UV) irradiation, with acrylic acid (AA) monomer added as a crosslinker without the addition of any other photo-initiator. The swelling behaviors, intermolecular chemical bonds, molecular structures, thermal behaviors, degrees of crystallinity, morphologies of the surfaces and internal structure, and their relationship to the AA content were characterized using Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Poly(acrylic acid) (PAA) and its chemical crosslinks formed in hydrogel films via free-radical reactions were confirmed using FTIR and DSC analyses. The XRD patterns indicated that the degree of crystallinity of the hydrogel films decreased as the PAA content was increased. SEM micrographs showed that a uniform interconnected pore structure was formed through the entire hydrogel structure, and a gradient in the crosslinking density through the film thickness was observed to result from extended irradiation times. The swelling behaviors revealed that the formation of PAA and its crosslinking in the hydrogel thin films improved the pH stability and controlled the degree of swelling while retaining a high swelling rate. The successful formation of chemical crosslinking without any specific photo-initiator improves the natural characteristics of CTS and PVA and imparts the resulting PVA/CTS hydrogel thin films with properties that make them very promising in biomedical applications.     

Surface modified graphene oxide/poly(vinyl alcohol) composite for enhanced hydrogen gas barrier film

A series of novel polyethyleneimine (PEI) modified graphene oxide (PEI-mGO) filled poly(vinyl alcohol) (PVA) nanocomposite (PEI-mGO/PVA) films were prepared by solution-casing for hydrogen gas barrier applications. Hydrophilic PEI was used to simultaneously reduce and modify graphene oxide sheets, thereby facilitating a homogeneous dispersion of PEI-mGO in the PVA matrix. The effects of PEI-mGO on the morphology and properties of the nanocomposite films were examined by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis and field emission scanning electron microscopy. Analogous GO/PVA composites were also prepared and characterized for comparative purposes. The PEI-mGO/PVA nanocomposites showed higher thermal and mechanical stability as well as remarkable improvement in hydrogen gas barrier properties compared to the PVA film; specifically, the PEI-mGO/PVA film having 3.0 wt% of PEI-mGO content exhibited almost 95% decrease in GTR and permeability values compared to PVA film.     

Study on the nonisothermal crystallization behavior of poly(vinyl alcohol)/attapulgite nanocomposites by DSC analysis

Attapulgite (AT)‐reinforced poly(vinyl alcohol) (PVA) nanocomposite films were prepared by solution‐casting technique. The nonisothermal crystallization behaviors of PVA bulk and PVA/AT nanocomposites have been investigated by differential scanning calorimetry (DSC). It has been found that the uniformly dispersed AT nanorods in the matrix have great influence on the glass transition temperature and crystallization behavior of PVA matrix. The Jeziorny method has been employed to analyze the DSC data. The results show that Jeziorny method could describe this system very well. Comparing with the PVA bulk, PVA/AT nanocomposites have higher crystallinity X_t, shorter semicrystallization time t_1/2, and higher crystallization rate constant Z_c. It can be concluded that AT can be used as an effective nucleating agent and has effects on the growth of crystallites in the crystallization process of PVA matrix. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 534–540, 2006     

Improved mechanical properties of poly (vinyl alcohol) films with glycerol plasticizer by uniaxial drawing

In this work, the uniaxial stretching poly (vinyl alcohol) (PVA) films with glycerol as plasticizer were prepared to explore the influence of drawing temperature and drawing ratio. The structure and property were investigated with scanning electron microscope, wide‐angle X‐ray diffraction, X‐ray diffraction, differential scanning calorimetry, mechanical tests, etc. With the increase of stretching temperature, the melting and crystallization temperatures increased. The tensile strength and Young modulus of glycerol/PVA films increased first and then decreased; when the temperature was 80°C, the tensile strength and Young modulus reached to maximum values of 197.2 and 470 MPa, respectively. In addition, with the increase of draw ratio, the orientation degree of the PVA molecular chains increased, indicating the improved regularity of molecular chains. When the PVA films were stretched to 4 times, the tensile strength and Young modulus of the films reached 162 and 143 MPa, respectively, which were 4 and 1.3 times compared with those of unoriented films. These environmentally friendly PVA films with excellent mechanical properties would find wide applications in the industry such as packaging, coating, etc.     

Melt‐blending of unmodified and modified cellulose nanocrystals with reduced graphene oxide into PLA matrix for biomedical application

In this article, we successfully fabricated the bionanocomposites using cellulose nanocrystals (CNCs) and reduced graphene oxide (rGO) reinforced into biodegradable polylactic acid (PLA) matrix through melt‐mixing method. Due to the affinity difference between hydrophilic CNC and hydrophobic PLA, the surface modification of CNC was employed using quaternary ammonium salts (CTAB) as a surfactant. The nanocomposites were developed using different blend ratios of CNC/modified CNC (1, 2, and 3) wt% and (0.5 wt%) rGO into the polymer matrix. The morphology of CNC, q‐CNC (modified CNC), and nanocomposites were inspected by atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). It is demonstrated from tensile tests that, the nanocomposite with 1 wt% CNC and rGO showed maximum tensile strength compared with PLA and its nanocomposites. Moreover, the nanocomposite with 1 wt% CNC and rGO was also having maximum thermal stability. From cytotoxicity evaluation, it is observed that all the nanocomposites are nontoxic and cytocompatible to HEK293 cells. In addition to this, the nanocomposite with q‐CNC showed enhanced barrier properties compared with PLA and PLA/CNC/rGO nanocomposite. The results obtained from different characterizations showed that the incorporation of surfactant onto CNC improved the dispersion in PLA but at the same time deteriorated the PLA matrix.     

Development of Nanocomposites from Bacterial Cellulose and Poly(vinyl Alcohol) using Casting-drying Method

Nanocomposites of bacterial cellulose (BC) and poly(vinyl alcohol) (PVA) were prepared by cast-drying method as an easy way in producing nanocomposite films and to expand the use of BC. The contribution of PVA in nanocomposites was evaluated by measurement of cross-sectional surface, moisture uptake and mechanical properties. Morphological analysis shows that PVA covered a number of cellulosic fibres and formed denser material as a function of PVA addition. Based on the tensile test, the addition of PVA causes a very slight reduction compared with bacterial cellulose itself. The BC/PVA nanocomposites still have similar stiffness to BC with elongation at break less than 5%, while PVA film shows ductile properties with elongation at break more than 80%. On the other hand, the presence of BC fibres in the PVA matrix enhanced the tensile strength and the elastic modulus of pure PVA about two to three times, but it decreased the toughness of pure PVA. The highest tensile strength and elastic modulus of the nanocomposites are 164 MPa and 7.4 GPa, respectively at BC concentration of 64%. Increasing BC concentration is proportional to reducing moisture uptake of BC/PVA nanocomposites indicating that the existence of BC fibres inhibits moisture absorption.     

氯化镁增塑改性聚乙烯醇

以氯化镁为增塑剂, 采用流延法制备了增塑改性聚乙烯醇(PVA). 研究了氯化镁与PVA的相互作用以及氯化镁增塑改性PVA的结晶性能、 热性能和机械性能. 研究结果表明, 氯化镁能与PVA大分子发生较强的相互作用, 从而破坏PVA分子链内和链间的氢键, 降低PVA的结晶度. 氯化镁对PVA的热性能影响显著, PVA在加入氯化镁后的热分解过程由纯PVA的两段失重过程转变成三段失重过程. 氯化镁可有效增塑PVA, 其玻璃化转变温度降低, 拉伸强度下降, 断裂伸长率上升, 储能模量下降.     

Rheological behavior of highly loaded cellulose nanocrystal/poly(vinyl alcohol) composite suspensions

Recent emphasis on the pilot scale production of cellulosic nanomaterials has increased interest in the effective use of these materials as reinforcements for polymer composites. An important, enabling step to realizing the potential of cellulosic nanomaterials in their applications is the materials processing of CNC/polymer composites through multiple routes, i.e. melt, solution, and aqueous processing methods. Therefore, the objective of this research is to characterize the viscoelastic behavior of aqueous nanocomposite suspensions containing cellulose nanocrystals (CNCs) and a water-soluble polymer, poly(vinyl alcohol) (PVA). Specifically, small amplitude oscillatory shear measurements were performed on neat PVA solutions and CNC-loaded PVA suspensions. The experimental results indicated that the methods used in this study were able to produce high-quality nanocomposite suspensions at high CNC loadings, up to 67 wt% with respect to PVA. Additionally, the structure achieved in the nanocomposite suspensions was understood through component attributes and interactions. At CNC loadings near and less than the percolation threshold, a polymer mediated CNC network was present. At loadings well above the percolation threshold, a CNC network was present, indicated by limited molecular weight dependence of the storage modulus. Overall, these results provide increased fundamental understanding of CNC/PVA suspensions that can be leveraged to develop advanced aqueous processing methods for these materials.     

尿素/乙醇胺复配增塑聚乙烯醇性能的研究

采用尿素/乙醇胺为复合增塑剂,利用流延法制备了增塑改性的PVA膜.通过FTIR法研究了尿素/乙醇胺复合体系与PVA的相互作用,采用XRD、DSC考察了增塑改性PVA膜的结晶性能和热性能.研究结果表明,乙醇胺作为尿素的良溶剂,能有效抑制尿素从PVA基体中析出.由尿素、乙醇胺组成的复合增塑剂能破坏PVA分子中的氢键作用、降低PVA的结晶度和熔点,对PVA的增塑作用显著.增塑改性后的PVA膜在水中的溶胀率(DS)下降,溶失率(S)增加.力学性能测试表明增塑改性后的PVA膜拉伸强度(TS)降低,断裂伸长率(E%)提高.含30phr尿素/乙醇胺的PVA膜的拉伸强度、断裂伸长率分别为23.89MPa和542.88%.     

Fabrication of a high-strength hydrogel with an interpenetrating network structure

Hydrogels have potential applications in many fields, but the poor mechanical strength has limited their further development. In this article, we designed a high-strength hydrogel with an interpenetrating network (IPN) structure from polyacrylamide (PAM) and poly(vinyl alcohol) (PVA). Synthesis parameters, such as PVA/AM mass ratio, crosslinker dosage and elongation time were carried out for high tensile strength and elongation. The results showed that chemical crosslinking, physical entanglement and PVA precipitates were the dominant parameters for the improvement of mechanical properties. The PVA structure transferred from crystal to amorphous due to intermolecular and intramolecular interactions (such as hydrogen bond and self-crosslinking). PVA precipitates scatterred in the brittle PAM matrix homogeneously which dispersed the applied stress and improved the hydrogel toughness. The tensile strength and elongation were extremely high, they were 2.4 MPa and 3100%, respectively. The simple method is versatile in synthesizing high-strength IPN hydrogels using many kinds of polymer species.     

Preparation and Characterization of Blend Films of Poly(Vinyl Alcohol) and Sodium Alginate

Blend films of poly(vinyl alcohol) (PVA) and sodium alginate (NaAlg) were prepared by casting from aqueous solutions. This blend films were characterized by tensile strength test, Fourier transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The miscibility in the blends of PVA and NaAlg was established on the basis of the thermal analysis results. DSC showed that the blends possessed single, composition‐dependent glass transition temperatures (T_gs), indicating that the blends are miscible. FT‐IR studies indicate that there is the intermolecular hydrogen bonding interactions, i.e. –OH…^?OOC– in PVA/NaAlg blends. The blend films also exhibited the higher thermal stability and their mechanical properties improved compared to those of homopolymers.     

Investigations of (PVA)0.7(NaBr)0.3(H2SO4)xM solid acid polymer electrolyte using positron annihilation lifetime spectroscopy

The free‐volumes of solid polymer electrolytes (SPE) were characterized using positron annihilation lifetime (PAL) spectroscopy, FTIR, and scanning electron microscope (SEM) techniques. The SPE based on poly(vinyl alcohol) (PVA) and sodium bromide (NaBr) complexed with sulfuric acid (SA) H₂SO₄ at different weight percent ratios were prepared using solution cast technique. The PAL results indicate that a higher SA content (more than 0.87 mol/L) in (PVA)_0.7(NaBr)_0.3 matrix increase the free‐volume hole size from 58 ų to 87 ų. The increase in the SPE free‐volume with higher SA content was associated with a decrease in the SPE crystallinity. It is postulated that the incorporated SA interrupt polymeric chain packing and retard crystallization during electrolyte films formation. The FTIR spectral studies indicate that the SA content higher than 0.87 mol/L induces chemical modifications within the PVA, which results in chain scission. The PAL study shows that the chain scissions within the polymer matrix affect the free volume hole density (I₃) and hence the microstructure. I₃ was found to be decreased from ?11 to ?6 %, resulting in lower fractional free‐volume holes in the SPE films. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2038–2044, 2010     

Novel Silver/Poly(vinyl alcohol) Nanocomposites for Surface‐Enhanced Raman Scattering‐Active Substrates

Summary: Surface‐enhanced Raman scattering (SERS)‐active substrates with high enhancement were prepared by an in situ reduction method. Novel silver/poly(vinyl alcohol) (PVA) nanocomposite films were obtained, in which the silver nitrate, poly(γ‐glutamic acid) (PGA), and PVA acted as precursor, stabilizer, and polyol reducant, respectively. The UV‐visible spectra of the as‐fabricated films showed that the surface plasmon resonance (SPR) absorption band was narrow and of a stronger intensity, which indicates that the Ag nanoparticle size distribution on the substrate was highly uniform. This finding was further confirmed by X‐ray diffraction (XRD), transmission electron microscopy (TEM), and field‐emission scanning electron microscope (FE‐SEM) measurements. It was found that a PGA‐stabilized PVA nanocomposite film revealed the presence of well‐dispersed spherical silver nanoparticles with an average diameter of 90 nm. The new substrate presents high SERS enhancement and the enhanced factor is estimated to be 10⁶ for the detection of benzoic acid.

The Raman scattering enhancement factor for the Raman spectra of benzoic acid on the various nanocomposite films.     

Structure evolution of α′‐phase poly(lactic acid)

Poly(lactic acid) films consisting of α′‐forms were prepared and uniaxially drawn. The effects of the draw rate at temperatures above the glass transition temperature on chain conformation, degree of crystallinity, and crystalline phase transformation were investigated by a combination of vibrational spectroscopy (infrared and Raman), differential scanning calorimetry, and wide‐angle X‐ray diffraction (WAXD). It was established that the α′‐crystal's phase of poly(lactic acid) films does not transform into either an α or β crystals on uniaxial drawing at a fixed draw ratio of 4. However, the degree of crystallinity was significantly increased on deformation. The structural change as a function of deformation also promotes an increase in the strain‐induced enthalpic relaxation endothermic peak appearing near the glass transition region. While the overall changes in physical properties can be attributed to the changes in the degree of crystallinity as a function of strain rate, polarized Raman spectra, and WAXD clearly illustrated changes and the differences in the amorphous and crystalline orientation as a function of processing conditions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1446–1454, 2011     

In situ production of nanocomposites of poly(vinyl alcohol) and cellulose nanofibrils from Gluconacetobacter bacteria: effect of chemical crosslinking

Nanocomposites of poly(vinyl alcohol) (PVA) reinforced with bacterial cellulose (BC) were bioproduced by Gluconacetobacter genus bacteria. BC was grown from a culture medium modified with water-soluble PVA to allow in situ assembly and production of a novel nanocomposite that displayed synergistic property contributions from the individual components. Chemical crosslinking with glyoxal was performed to avoid the loss of PVA matrix during purification steps and to improve the functional properties of composite films. Reinforcement with BC at 0.6, 6 and 14 wt% content yielded nanocomposites with excellent mechanical, thermal and dimensional properties as well as moisture stability. Young’s modulus and strength at break increased markedly with the reinforcing BC: relative to the control sample (in absence of BC), increases of 15, 165 and 680 % were determined for nanocomposites with 0.6, 6 and 14 % BC loading, respectively. The corresponding increase in tensile strengths at yield were 1, 12 and 40 %, respectively. The results indicate an exceptional reinforcing effect by the three-dimensional network structure formed by the BC upon biosynthesis embedded in the PVA matrix and also suggest a large percolation within the matrix. Bonding (mainly hydrogen bonding) and chemical crosslinking between the reinforcing phase and matrix were the main contributions to the properties of the nanocomposite.