Preparation and crystallization behavior of multiwalled carbon nanotubes/poly(vinyl alcohol) nanocomposites

The poly(vinyl alcohol) (PVA)‐based nanocomposites embedded with modified multiwalled carbon nanotubes (MWCNTs) were prepared. To enhance the interfacial interaction between MWCNTs and PVA, acid‐treated MWCNTs were grafted with PVA chains, compatibilizing MWCNTs and the matrix. The better dispersion of MWCNTs in PVA matrix was obtained by the introduction of MDI reaction bridges and then PVA molecules onto the surface of MWCNTs. Moreover, strong interaction between MWCNTs and PVA matrix was evidenced through the measurement results of the melting behavior, polarized Raman measurement, and nonisothermal crystallization behavior of the nanocomposites. Owing to the reinforcement of MWCNTs, the tensile strength and modulus of PVA nanocomposite containing 0.9 wt% MWCNTs were increased by 160.7 and 109.2%, respectively, compared to neat PVA. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

X‐ray diffraction and dynamic mechanical analyses of α‐chitin whisker‐reinforced poly(vinyl alcohol) nanocomposite nanofibers

Electrospinning is a facile method for preparing nanocomposite materials in fiber form. Nanomaterials that have been incorporated within such fibers are usually inorganic in nature. Recently, nanocomposite nanofibers based on poly(vinyl alcohol) (PVA) as the matrix and nanocrystals of α‐chitin (i.e. chitin whiskers; ca 31 nm in width and ca 549 nm in length on average) as the nanofiller have been successfully prepared. In the study reported here, the fibers were further investigated using X‐ray diffraction (XRD) and dynamic mechanical analyses in comparison with the corresponding solvent‐cast films. The average diameters of the PVA/chitin whiskers fibers ranged between 175 and 218 nm. Careful analysis of the wide‐angle XRD patterns of the fiber mats and the films showed that PVA was partially crystalline, and the incorporation of the whiskers within the fibers was confirmed by peaks characteristic to α‐chitin crystals. Dynamic mechanical analysis showed that the fiber mats were weaker than the films and that the relaxation temperatures associated with the glass transition (T_g) of the fiber mats were greater than those of the films. The addition and increasing the amount of the whiskers caused the crystallinity of PVA within the nanocomposite materials to decrease and T_g to increase. The present study shows that the geometry of nanocomposite materials plays a major role in determining their properties. Copyright © 2009 Society of Chemical Industry     

Improving interfacial interaction of l‐phenylalanine‐functionalized graphene nanofiller and poly(vinyl alcohol) nanocomposites for obtaining significant membrane properties: Morphology,thermal, and mechanical studies

In polymer nanocomposite synthesis, the challenges are achieving well dispersion of nanofiller and its maximum interfacial interaction with polymer matrix at low loading percent. In this study, the preparation of poly (vinyl alcohol) (PVA) nanocomposites with l ‐phenylalanine‐functionalized graphene (f‐graphene) using a simple water solution processing method is reported. Graphene layers were functionalized with l ‐phenylalanine amino acid as a biocompatible and environmentally friendly modifier. The obtained PVA/f‐graphene nanocomposite membranes were smooth, uniform, and flexible. Efficient interaction was found between f‐graphene and PVA matrix, which caused significant improvement in mechanical and thermal properties of the graphene‐based nanocomposite with homogeneous dispersion. POLYM. COMPOS., 37:1924–1935, 2016. © 2015 Society of Plastics Engineers     

Evaporation behaviour of water and its plasticizing effect in modified poly(vinyl alcohol) systems

Several modified poly(vinyl alcohol) (PVA) systems with various plasticizers were prepared and their melt‐processing was successfully realized. This paper focuses on the study of the evaporation behaviour of water in these modified PVA systems, exploring its plasticizing mechanism by using differential scanning calorimetry. The evaporation characteristics of bulk water, water in aqueous solutions of the plasticizers, and the thermal properties of PVA were also studied. The experimental results show that water in aqueous solutions of glycerol and/or caprolactam evaporates at a lower temperature than bulk water, but water in the PVA/water system evaporates at a higher temperature, with a wider DSC peak due to the interaction between water and PVA. Incorporation of glycerol, caprolactam or their mixtures further strengthens the interactions between water and the other components, retarding water evaporation. During the processing, the less closely associated water has the plasticizing effect through molecule movement, while the strongly bound water, which breaks the intermolecular hydrogen bonding of PVA and decreases its intermolecular interaction, is more beneficial to the melt‐processing of PVA. Copyright © 2003 Society of Chemical Industry     

Extremely oriented tunicin whiskers in poly(vinyl alcohol) nanocomposites

In order to utilize the excellent mechanical properties of cellulose whiskers (CWs) along their length, the present work was undertaken to embed CWs with highly oriented forms in a polymer matrix. Nanocomposite fibers were prepared using poly(vinyl alcohol) (PVA; degree of polymerization of 1500) as the matrix and a stable aqueous suspension of CWs extracted from tunicates as the reinforcing phase. Macroscopically homogeneous suspensions of PVA–CW were gel‐spun in a methanol coagulating bath. The as‐spun fibers included CWs oriented along the fiber axis and showed a significant increase in dynamic storage modulus. Hot drawing of the PVA–CW as‐spun fibers to their maximal draw ratio led to extremely high orientation of the CWs together with a drastic reduction in voids in the fiber matrix. Outstanding mechanical properties of the drawn composites were obtained by the incorporation of only a small amount (1 wt% of solid PVA content) of CWs. The stress transfer mechanism in the fibers was studied using an X‐ray diffraction technique by applying stress to the whole composite with in situ monitoring of stress on the incorporated CWs. The applied external stress was found to be translated efficiently to the incorporated CWs through the PVA matrix, suggesting strong interfacial bonding between filler and matrix. The strong interaction and efficient stress transfer between matrix and filler are suggested as the cause for the observed improvements in mechanical properties of the composites. Copyright © 2011 Society of Chemical Industry     

Preparation and characterization of graphene/poly(vinyl alcohol) nanocomposites

Graphene (GE)‐based nanocomposites are emerging as a new class of materials that hold promise for many applications. In this article, we present a general approach for the preparation of GE/poly(vinyl alcohol) (PVA) nanocomposites. The basic strategy involved the preparation of graphite oxide from graphite, complete exfoliation of graphite oxide into graphene oxide sheets, followed by reduction to GE nanosheets, and finally, the preparation of the GE/PVA nanocomposites by a simple solution‐mixing method. The synthesized products were characterized by X‐ray diffraction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetry, and differential scanning calorimetry analysis. The GE nanosheets were well dispersed in the PVA matrix, and the restacking of the GE sheets was effectively prevented. Because of the strong interfacial interaction between PVA and GE, which mainly resulted from the hydrogen‐bond interaction, together with the improvement in the PVA crystallinity, the mechanical properties and thermal stability of the nanocomposites were obviously improved. The tensile strength was increased from 23 MPa for PVA to 49.5 MPa for the nanocomposite with a 3.25 wt % GE loading. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Melt‐processable and self‐healing poly(vinyl alcohol) elastomer containing diol groups in the side chain

A 3‐amino‐1,2‐propane diol functionalized poly(vinyl alcohol) elastomer (PVA–COO–AP) with melt processability and self‐healing properties was prepared by chemical graft modification, that is, a poly(vinyl alcohol) (PVA) carboxylation and carbodiimide reaction. Unlike that of conventional PVA modifiers, the incorporation of diol groups in the 3‐amino‐1,2‐propane diol molecules onto PVA chains reduced the breaking of intrinsic hydrogen‐bonding interactions of PVA because of the formation of new hydrogen bonds between the diol groups and the hydroxyl groups of PVA. PVA–COO–AP possessed a lower melting temperature and a higher decomposition temperature than PVA; this enabled the melt processing of PVA. The PVA–COO–AP samples prepared by compression molding exhibited excellent flexibility and elasticity, and the samples with a lower glass‐transition temperature below ambient temperature could be self‐healed because of the existence of dynamic hydrogen bonds. AP–COO–AP is believed to have potential applications in the fields of fibers and biomedical membranes. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46050.     

Development of potentially biodegradable polyamide‐6 and polyvinyl alcohol blends: Physico‐mechanical properties,thermal properties,and soil test

Blends of polyamide‐6 with 5, 7.5, 10, 15, and 20 wt % of polyvinyl alcohol (PVA) were prepared by the extruding in a corotating twin‐screw extruder. The extrudate strands were cut into pellets and injection‐molded to make test specimens. These specimens were tested for physico‐mechanical properties such as tensile strength, impact strength, density, water absorption, hardness, and thermal characteristics by differential scanning calorimetry, heat distortion temperature (HDT), vicat softening point (VSP), and melt flow index. The prepared blends show enhanced biodegradation, water absorption, and density, but it is observed that the introduction of PVA into the polyamide–6 matrix shows considerable reduction in tensile strength, impact strength, HDT, VSP, and hardness initially, but subsequent addition does not show significant reduction because of the enhanced interaction between amide groups of polyamide‐6 and hydroxyl groups of PVA. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2339–2346, 2005     

Preparation of poly(vinyl alcohol) and hydroxypropyl‐β‐cyclodextrin inclusion complex through polymer processing

In this study, inclusion complexes (ICs) between host hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) and guest poly(vinyl alcohol) (PVA) were prepared through polymer processing with water as plasticizer and solvent. The structure of PVA/HP‐β‐CD ICs was confirmed by FTIR, ¹H‐NMR and 2D‐NOESY NMR. The yields of PVA/HP‐β‐CD ICs were 62.5%, 51.4%, and 46.8% in twin‐screw, rotor and single‐screw processing, respectively. The crystallinity, thermal properties and mechanical properties of the PVA/HP‐β‐CD ICs were characterized by X‐ray diffraction, differential scanning calorimetry, thermal gravimetric analysis and tensile tests, respectively. The results indicated that HP‐β‐CD could establish strong interfacial interaction with PVA through hydrogen bonding and form ICs with PVA. As a result, crystallinity and melting temperature decomposition temperature of PVA were decreased. Compared with pure PVA, PVA/HP‐β‐CD ICs exhibited remarkable improvement in thermal stability. Moreover, the tensile strength, elongation at break and torque of ICs with different content of HP‐β‐CD were discussed. POLYM. ENG. SCI., 55:1988–1993, 2015. © 2014 Society of Plastics Engineers     

Dual‐bonding structured ternary composite film of poly(vinyl alcohol)–boric acid–nanodiamond

Ternary composite films of poly(vinyl alcohol) (PVA), boric acid (BA), and detonation nanodiamond (DND) were prepared by aqueous solution method. Because of its excellent mechanical/thermal properties and low friction coefficient, DND is expected to offer PVA film superior performance if the puzzles of particle agglomeration in polymer matrix and fragile interface reaction between DND and PVA can be settled. BA was used as a crosslinking agent to form a strong network structure between DND and PVA. Investigation on microstructure of PVA/BA/DND films and bonding mechanisms therein shows that BA, DND, and PVA may crosslink by oxo‐bridges owing to the interaction of hydroxyl groups. The Young's modulus (E) of composite films was enhanced by nearly 3.3 times with only 0.8 wt % DND loading, and the antiwear, thermal stability, and waterproof properties can be significantly improved after the crosslinking. Meanwhile, the transparency of composite films can be well preserved even with large DND content. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45449.     

Intraply and interply hybrid composites based on E‐glass and poly(vinyl alcohol) woven fabrics: tensile and impact properties

E‐glass and poly(vinyl alcohol) (PVA) fibres were used to produce both homogeneous and hybrid composites with an orthophthalic unsatured polyester resin. Results are presented regarding the tensile and impact behaviour of both intraply and interply hybrid composites, with particular regard to the effects of the plies stacking sequence and the loading direction. With a proper choice of composition and stacking sequence, E‐glass/PVA hybrid composites were proved to achieve a property profile superior to those of homogeneous E‐glass laminates in terms of specific properties. In particular, hybridization with PVA fibres resulted in improving the specific impact energy of E‐glass laminates. Resistance to impact crack propagation was higher for intraply with respect to interply hybrid composites, as evidenced by their ductility index values. Copyright © 2004 Society of Chemical Industry     

Anomalous behavior of the dielectric and electrical properties of polymeric nanodielectric poly(vinyl alcohol)–titanium dioxide films

The complex dielectric permittivity, alternating‐current electrical conductivity, electric modulus, and impedance spectra of polymeric nanocomposite (PNC) films consisting of a poly(vinyl alcohol) (PVA) matrix dispersed with nanosize particles of titanium dioxide (TiO₂); (i.e., PVA–x wt % TiO₂, where x is 0, 1, 3, or 5) were investigated in the frequency range 20 Hz to 1 MHz at ambient temperature. A detailed analysis of the results showed that the values of the dielectric and electrical parameters of these PNC‐based nanodielectric films varied anomalously with increasing TiO₂ concentration. The temperature‐dependent dielectric characterization of the PVA–3 wt % TiO₂ film revealed that the dielectric polarization at a fixed frequency increased nonlinearly with increasing temperature. The temperature‐dependent electric modulus relaxation time values of the nanodielectric film obeyed Arrhenius behavior. The X‐ray diffraction study confirmed that the crystalline phase of the PVA matrix decreased with increasing TiO₂ concentration; this suggested that the interaction of the TiO₂ nanoparticles caused some destruction of the hydroxyl group dipolar ordering in the hydrogen‐bonded crystalline structure of the pristine PVA matrix. The intensities of the diffraction peaks of the TiO₂ nanofiller were enhanced as its concentration increased in these nanodielectrics; this confirmed the existence of TiO₂ nanoparticles inside the crystalline phases of the PVA matrix. The surface morphology of the films was examined by the study of their scanning electron micrographs. The feasibility of using these flexible polymeric nanodielectric films as electrical insulators and dielectric substrates in low‐power microelectronic devices operated at audio‐ and radio‐frequency electric fields was explored. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44568.     

Drug‐release behavior of chitosan‐g‐poly(vinyl alcohol) copolymer matrix

Chitosan‐g‐poly(vinyl alcohol) (PVA) copolymers with different grafting percent were prepared by grafting water‐soluble PVA onto chitosan. The drug‐release behavior was studied using the chitosan‐g‐PVA copolymer matrix containing prednisolone in a drug‐delivery system under various conditions. The relationship between the amount of the released drug and the square root of time was linear. From this result, the drug‐release behavior through the chitosan‐g‐PVA copolymer matrix is shown to be consistent with Higuchi's diffusion model. The drug‐release apparent constant (K_H) was slightly decreased at pH 1.2, but increased at pH 7.4 and 10 according to the increasing PVA grafting percent. Also, K_H was decreased by heat treatment and crosslinking. The drug release behavior of the chitosan‐g‐PVA copolymer matrix was able to be controlled by the PVA grafting percent, heat treatment, or crosslinking and was also less affected by the pH values than was the chitosan matrix. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 458–464, 1999     

Rheological behavior and network dynamics of silica filled vinyl‐terminated polydimethylsiloxane suspensions

Present article reports the rheological properties and network dynamics of fumed silica filled vinyl‐terminated polydimethylsiloxane suspensions. The results reveal that as filler loading increases, the span of the linear viscoelastic region with constant dynamic storage modulus is narrowed with increase in strain amplitude while the relaxation time of the compounds get shifted to longer time scales. The dynamics of filler‐network indicated significant Payne effect due to fumed silica incorporation into the PDMS matrix. Further, strain‐induced agglomeration of fumed silica particles, characterized by a peak in the dynamic loss modulus curve could also be observed. High loss‐tangent was observed for lower contents of filler in the suspension, an effect with an apparent relationship to the loosely formed filler‐network. The formation of a saturated network structure of fumed silica particles was evident from the dynamic modulus and complex viscosity data, that remained unaffected with frequency till a critical amount of fumed silica loading. Han plots (storage modulus versus loss modulus) revealed the microstructural changes for various filled systems that was attributed to build‐up of the filler‐network causing an apparent evolution of yielding phenomenon. Van Gurp‐Palmen plots (complex modulus versus phase lag) showed that flow behavior of the filled PDMS suspensions resembled to that of typical viscous fluids. POLYM. ENG. SCI., 57:973–981, 2017. © 2016 Society of Plastics Engineers     

Structural properties of CrF3‐ and MnCl2‐filled poly(vinylalcohol) films

Poly(vinylalcohol) (PVA) films filled with different filling levels of CrF₃ and MnCl₂ have been prepared by the casting method. Differential scanning calorimetry (DSC) and X‐ray diffraction (XRD) analysis were used to study the changes in structure properties that occur due to filling. The changes occurring in the measured parameters with increasing the filler content was been interpreted in terms of the structural modification of the PVA matrix. It was found that all studied samples had the main melting temperature due to the main crystalline phase of PVA. The intensity and position of this peak depended on the filling level. On the other hand, the samples of CrF₃‐filled PVA films with filling level W ≥ 10 wt % revealed another melting temperature, indicating the presence of a new crystalline phase besides the main crystalline phase. Changes occurring in the degree of crystallinity of the studied samples were discussed. The calculated degree of crystallinity was formulated numerically to be an exponential function of filling level. The X‐ray diffraction patterns of the studied samples confirmed the DSC results. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 516–521, 2003     

Properties and morphology of poly(vinyl alcohol) blends with sago pith bio‐filler as biodegradable composites

The effects of sago pith as a bio‐filler (SPB) on the mechanical and thermal properties of poly(vinyl alcohol) (PVA) were studied. The SPB was obtained from sago pith waste after starch extraction from sago palm. Sago pith waste was dried and ground to produce SPB. The SPB was blended with PVA in a twin‐screw co‐rotating extruder in order to produce PVA‐SPB composites for mechanical, morphology, and thermal analyses. Blending of SPB and PVA improved the tensile modulus, whereas the tensile strength was reduced. This result occurred because SPB increased the rigidity of PVA. However, lack of interfacial adhesion between PVA and SPB caused the loss of reinforcing effects. The morphology analysis showed that a high loading of SPB (>70 wt%) tended to form clusters, as implied by the presence of elongated cavities due to droplet coalescence restricting chain mobility. Besides that, the enthalpy of melting (ΔH_m) for 50 wt% of SPB was higher than that of PVA. This observation means that the molecular interaction forces between PVA and SPB were so great as to overtake those of the PVA itself. Thus it was concluded that 40–50 wt% of SPB was preferably blended with PVA to form a biodegradable composite in order to reduce the overall materials cost, rather than to act as a strong reinforcing filler. J. VINYL ADDIT. TECHNOL., 2011. © 2011 Society of Plastics Engineers     

Nitrofurazone‐loaded PVA–PEG semi‐IPN for application as hydrogel dressing for normal and burn wounds

Hydrogels have been used in a wide variety of biomedical devises, particularly in the field of drug delivery, tissue engineering, and wound healing. In this study, a polyvinyl alcohol (PVA)–polyethylene glycol (PEG) semi‐interpenetrating hydrogel network (IPN)‐based wound dressing system containing nitrofurazone (NFZ) was synthesized by chemical crosslinking technique. The introduction of PEG to PVA matrix led to reduction in the water vapor transmission rate, which in‐turn resulted in improved healing activity. Drug‐loaded IPNs were prepared by mixing aqueous solution of NFZ with the optimized PVA–PEG formulation subsequent to the crosslinking step. The in vitro diffusion studies of NFZ indicated a relatively slow release of drug resulting from its microencapsulation in the polymeric matrix. Subsequently, in vivo wound healing efficacy toward acute and burn wound healing in experimental rats was investigated. Semi‐IPN hydrogel loaded with NFZ dressing improved the overall healing rate in both acute and burn wounds, as evidenced by significant increase in total protein, hydroxyproline and hexosamine contents. Histological examinations also correlated well with the biochemical findings. A faster wound contraction was also observed in hydrogel treated acute and burn wounds. The results indicated that PVA–PEG semi‐IPN hydrogel based dressing systems containing NFZ could be used as an effective wound dressing material. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Enhanced CO2 separation performance by PVA/PEG/silica mixed matrix membrane

This article focused on segregation of low concentration CO₂ from CO₂/N₂ mixture gas by implementing high‐performance facilitated transport mixed matrix membranes (MMMs) in large‐scale carbon capture techniques. These advanced, novel CO₂‐selective membrane materials were developed by embedding silica nanoparticles at different loading into the poly(vinyl alcohol) (PVA)/poly(ethylene glycol) (PEG) matrix using solution casting. In situ sol–gel technique was applied for the synthesis of the hydrophilic SiO₂ nanoparticles. The compatibility of filler‐polymer matrix plays a crucial role in the optimization of the membrane performance. The dispersion and interaction of the filler into the polymer matrix were confirmed by thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, X‐ray diffraction, field emission scanning electron microscopy, contact angle tests, and swelling ratio analysis. Field emission scanning electron microscopy analysis of the synthesized MMMs established the homogeneous dispersion of the fillers in the polymer matrix. Owing to its good compatibility with PVA/PEG matrix, the inclusion of fillers significantly increased the overall separation efficiency of CO₂ within the membrane. Compared to pristine PVA/PEG membrane, PVA/PEG/silica membrane with 3.34 wt % silica loading showed pronounced improvement in its gas separation properties with 78% augmentation in CO₂ permeability and 45% enhancement in CO₂/N₂ selectivity for fixed conditions pertaining to sweep side water flow rate of 0.04 mL/min and 100 °C temperature. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46481.     

Structural properties of CrF3‐ and MnCl2‐filled poly(vinyl alcohol) films

Poly(vinyl alcohol) (PVA) films filled with different amounts of CrF₃ and MnCl₂ were prepared by the casting method. Differential scanning calorimetry (DSC) and X‐ray diffraction (XRD) analysis were used to study the changes in the structure properties that occurred because of filling. The changes occurring in the measured parameters with increasing filler contents were interpreted in terms of the structural modification of the PVA matrix. All the studied samples had a main melting temperature due to the main crystalline phase of PVA. The intensity and position of this peak depended on the filling level. However, the samples of CrF₃‐filled PVA films with a filling level greater than or equal to 10 wt % revealed another melting temperature, which indicated the presence of a new crystalline phase in addition to the main crystalline phase. The changes that occurred in the degree of crystallinity of the studied samples were examined. The calculated degree of crystallinity was formulated numerically to be an exponential function of the filling level. The XRD patterns of the studied samples confirmed the DSC results. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1115–1120, 2003     

Designing of fullers‐earth‐containing poly(vinyl alcohol)‐g‐poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid) nanocomposites: Swelling and deswelling behaviors

In this study, polymer–clay nanocomposites (PCNs) composed of poly(vinyl alcohol)s (PVAs), poly(2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid), and fullers earth were prepared by the effective dispersal of inorganic nanoclays in the organic PVA matrix via in situ free‐radical polymerization with potassium persulfate as an initiator and N,N‐methylene bisacrylamide as a crosslinker. The monomer, 2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid, was grafted onto the PVA backbone, and at the same time, fullers earth layers were intercalated and exfoliated into the grafted copolymer, especially at a low or moderate loading of the fullers earth. The synthesized PCN materials were characterized by Fourier transform infrared spectroscopy and wide‐angle X‐ray diffraction techniques. The morphological features of the synthesized materials were studied by scanning electron microscopy; this revealed that the swelling ratio of this nanocomposite increased with increasing fullers earth content. The X‐ray diffraction results indicated that the fullers earth was exfoliated in the nanocomposite matrix, and its introduction into the polymer matrix enhanced the percentage crystallinity of the polymer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010