Increasing PVA Content Research Articles

Vapour permeation characteristics of aliphatic alcohols through PVA/PVC thin films

Nonsolvent induced phase separation (NIPS) method using NMP/water system was adopted to prepare PVA/PVC thin films and were characterized by FTIR & FE-SEM analysis. Mechanical strength measurements indicated that an optimum composition of PVA/PVC has maximum tensile strength and might be due to the intercalation of viscous PVA into the stiff PVC matrix. Degree of swelling (DS) and water contact angle (WCA) measurements showed greater wettability of the films with increasing PVA content as is revealed from the higher film porosity and diminished contact angle. Pure water flux (PWF) and mean pore size were studied to determine the water permeation capacity of the film. Vapour permeability of various films was evaluated by using three different aliphatic alcohols viz. Methanol, ethanol and propanol. Barrier property and selectivity in permeation were studied for a particular PVA/PVC composition with moderate number and size of the pores which exhibited minimum permeation capacity.

Synthesis of PVA/TiO2 Composite Layer over Conductive Textile Sheet Using Electrospinning Method for Enhancing Self-Cleaning Properties

The present research used the electrospinning method to apply a polyvinyl alcohol/titanium dioxide (PVA/TiO2) layer over a conductive textile (70 % polyester and 30 % cotton) sheet. PVA with 10, 12.5, and 15 g concentrations was mixed into 100 ml distilled water. Then, each PVA solution was mixed with 1.5 wt.% of TiO2. Afterward, the electrospinning method applied a PVA/TiO2 composite onto a conductive textile sheet. Various characterizations were conducted, such as resistivity, scanning electron microscopy (SEM), Fourier transforming infrared (FTIR), and photocatalytic activity. The resistivity result is 9.5, 10, and 10  for A, B, and C samples. According to SEM investigation, higher PVA concentration leads to higher fiber sizes around 0.65 µm. An increase in PVA content does not affect the bands that were formed. The size of the fiber diameter contributed to the photocatalytic activity of MB. A smaller fiber diameter could enhance photocatalytic activity.

Effects of Type and Content of Fibers, Water-to-Cement Ratio, and Cementitious Materials on the Shrinkage and Creep of Ultra-High Performance Concrete.

The effects of the type and content of fibers, water to cement ratio (W/C), and content of cementitious materials on the shrinkage and creep of ultra-high performance concrete (UHPC) were investigated. The relationships between curing age, shrinkage, and unit creep of the UHPC were also discussed. The results showed that the shrinkage of the UHPC decreased with the increase in W/C, where there existed a quadratic function between shrinkage and W/C. However, the unit creep of the UHPC increased with W/C. The shrinkage and unit creep of the UHPC increased with the increase in the content of the cementitious materials. The type and content of fibers had different effects on the shrinkage and unit creep of the UHPC, that is, the shrinkage of the UHPC first increased and then decreased with the increase in the content of steel fibers, where there existed a quadratic function between them. There was a linear function between the shrinkage of the UHPC and the content of carbon fibers, but the shrinkage of the UHCP first increased and then decreased with the increase in PVA content. The shrinkage and unit creep of the UHPC at the initial curing age were significant, which tended to be constant with the increase in curing age. Although the steel fibers had a significant inhibiting effect on the unit creep of the UHPC, the carbon fibers and PVA had positive and negative effects on the unit creep of the UHPC. The effects of the type and content of fibers on the shrinkage and unit creep of the UHPC were caused by the slenderness ratio, shape, surface roughness, and elasticity modulus of the fibers. The shrinkage and creep of the UHPC were caused by the chemical autogenous shrinkage and free water evaporation of the UHPC.

Design and evaluation of sodium alginate/polyvinyl alcohol blend hydrogel for 3D bioprinting cartilage scaffold: molecular dynamics simulation and experimental method

To determine the optimum composition of AS/PVA for bioprinting cartilage scaffold, a molecular simulation combining experimental method was employed to investigate the microstructure, physicochemical properties and printability of AS/PVA blending hydrogels at different compositions. The compatibility analysis results show that SA and PVA have a good compatibility, they are miscible at any compositions. Mechanical properties analysis indicates that the tensile strength of 8SA/2PVA is the best, and compared with 8SA/2PVA, 7SA/3PVA possesses a better toughness and similar tensile strength. Moreover, FFV value and pore size decrease with the increase of PVA content, indicating the incorporation of PVA makes the system denser and pore size smaller, and the hydrogel of 8SA/2PVA possesses the optimal pore structure for the proliferation of chondrocytes. The main reason behind the conclusions obtained above is attributed to the strong hydrogen bond and intermolecular interaction between SA and PVA molecular chains. Finally, the results of printability indicates that, due to the fluidity of PVA, the forming quality becomes worse with the increase of PVA content, and when the PVA content in hydrogel precursors is within 30 wt.%, the forming quality is relatively good. Comprehensive considering the results above, the blend hydrogel of 8SA/2PVA was selected out and considered to be the most suitable for 3D printing cartilage scaffolds.

Preparation of hydrophilic polyvinylidene fluoride/polyvinyl alcohol ultrafiltration membrane via polymer/non-solvent co-induced phase separation method towards enhance anti-fouling performance

Membrane separation is a common water treatment technology, but the problem of membrane fouling should not be ignored. Hydrophilic modification is an effective method to reduce membrane fouling. Therefore, PVA/non-solvent co-induced phase separation method was proposed to achieve PVDF ultrafiltration membrane hydrophilic modification and structural control with high concentration polymer coagulation bath. PVA was uniformly distributed on the surface and inside of the hydrophilic modified membrane, which was stable and not easy to leach during filtration. With increasing PVA content in coagulant, the phase separation process changed from instantaneous to delayed, and the membrane surface changed from dense to spherulitic particle accumulation structure, while the connectivity of sponge pores was enhanced until it was completely transformed into a uniform spherical particle structure. The irreversible pollution rates of the modified membrane were 3.28% and 3.48%, respectively, which were significantly lower than those of the unmodified PVDF membranes (25% and 15.26%, respectively) when filtering simulate municipal wastewater with protein and humic acid. The flux recovery rate of the modified PVDF membrane was basically maintained above 90%. This study was a one-step method for membrane structure optimization and hydrophilic modification and contributed a theoretical basis for the role of high concentration polymer coagulant in the membrane forming process.

Crystalline structure and reinforcement in hybrid PP composites

Hybrid composites were prepared from a PP homopolymer, talc and PVA fibers by twin-screw extrusion and injection molding. Talc was added to improve stiffness, while the fibers serve to increase impact resistance. Mechanical properties were characterized by tensile and impact testing, while structure was studied by SEM and optical microscopy. The results showed that talc has a strong nucleating effect in the PP used in spite of the fact that the grade contained a nucleating agent inherently. PVA also nucleated the PP slightly, with trans-crystallization occurring around the fibers. The effect of the two components was independent of each other on lamella thickness, but crystallinity decreased with increasing PVA content in the hybrid composites. The results clearly showed that crystalline structure changes considerably upon the addition of the two components, both lamella thickness and crystallinity increasing. However, somewhat contradictorily, the effect of these changes on the mechanical properties of the composites is small. Model calculations have shown that stiffness increases by about 0.5 GPa due to nucleation, while moduli as large as 7 GPa are reached by the addition of talc. Impact resistance is completely independent of lamella thickness or crystallinity; this property is determined mainly by local deformation processes initiated by the PVA fibers. Dispersed structure and the direct effect of the additive determine properties in the hybrid composites studied, and the role of crystalline structure is of secondary importance.

Intrinsic effect of hybrid fibres 3D network on the electrochemical characteristics of Ultra-High Performance Fibre Reinforced Composites (UHPFRC)

This study addresses the intrinsic effect of hybrid fibres 3D network on the electrochemical characteristics of Ultra-High Performance Fibre Reinforced Composites (UHPFRC), including experimental investigations and mechanism analysis. Firstly, the matrix of the UHPFRC is fabricated based on the modified Andreasen & Andersen model. Then, three types of fibres (long steel fibre (LSF), short steel fibre (SSF) and polyvinyl alcohol fibre (PVA)) are further incorporated into the developed UHPFRC to generate different hybrid fibres 3D network. After that, the mechanical properties, chloride permeability and electrochemical properties of the designed UHPFRC with hybrid fibres are analyzed. The obtained results exhibit that with an increase of PVA content, the steel fibre network can be significantly disturbed, and the capacity of designed UHPFRC almost decrease linearly. In contrast, the added SSF cause that the capacity of UHPFRC with hybrid will decrease firstly and then increase. This implies that there is a balance point for the fibres hybridization design, with which the electrochemical corrosion resistance and mechanical properties of UHPFRC can be well optimized. At last, X-ray CT is further employed to quantitatively understand the fibres 3D network structure of the developed UHPFRC.

The preparation of a straw engineering sand-fixing plank and its sand-fixing and replanting performance exploration

To improve the shortcoming of sand fixation in traditional engineering, the study prepares a kind of porous composite for sand fixation and replanting by taking waste straw as the skeleton, polyvinyl alcohol and aquasorb as the composite agent, then pressing moulding by a press machine. Firstly, the effect of PVA on the mechanical properties is studied by sheering strength. In addition, the fracture mechanism of the composite is analysed by infrared spectrum of the PVA and photos under the optical microscope. Then, it is studied the influence of the amount of aquasorb on the water absorption and retention ability of the composite through the water absorption ratio and water content. Besides, the good water retention and replanting performance of aquasorb is visualized through the macro humidity contrast. The results show that, with the increase of PVA content, its sheering strength first decreases and then increases to the peak value, which is as high as 4.79MPa. It can be seen through the analysis of fracture morphology, that the composite crosslinking of PVA and aquasorb forms a three-dimensional network structure. And the structure enhances the toughness of the composite. With the increase of the content of the aquasorb, the water absorption ratio and the water content first increase and then decrease. When the content is 33.33%, the effect reaches to the optimal level, the water absorption ratio reaches to 3.76 and the repeated water absorption ratio reaches to 2.71. What’s more, the water content is always higher than other proportions. Therefore, the composite can effectively cooperate with plants and extend the years of sand control. The study provides a new idea and basis for the combination of sand fixation and waste straw.

Enzyme immobilization in cage-like 3D-network PVA-H and GO modified PVA-H (GO@PVA-H) with stable conformation and high activity

In this work, polyvinyl alcohol hydrogel (PVA-H) and graphene oxide doped polyvinyl alcohol hydrogel (GO@PVA-H) with cage-like 3D network structure were synthesized by freeze/thaw recycling method and used for the immobilization of horse radish peroxidase (HRP). The variations of the network structures in PVA-H and GO@PVA-H were investigated under varied conditions. With the increasing PVA content (4–12%) and stirring time, both PVA-H and GO@PVA-H were tended to form more uniform pores and cage-like structure as well as smaller channel size. When GO was introduced, the stirring time was reduced to achieve appropriate mixing during the GO@PVA-H synthesis, compared to PVA-H with the same PVA content. HRP could be caged in PVA-H and GO@PVA-H and remained relatively high enzymatic activity. Experimental results showed that the structure and configuration of PVA-H and GO@PVA-H had significant effects on the enzyme accessibility and the conformational transformation of immobilized HRP. The structure analysis showed that the enzymatic conformation of HRP was changed by the immobilization under different conditions. The conformational transformation of immobilized HRP was restrained effectively in GO@PVA-H. After improving the structure of PVA-H and GO@PVA-H, the immobilized HRP acquired high dispersity, good accessibility and stable conformation, showed high-efficient activity similar as free HRP. Compared to PVA-H, not only the immobilization rate of HRP in GO@PVA-H but also the stability and reusability of HRP in the degradation of bisphenol A (BPA) was all improved. Therefore, PVA-H and GO@PVA-H were efficient in terms of storage and recycle of free enzymes in water treatment.

Development and characterization of poly(vinyl alcohol) and casein blend films

AbstractBlends of plasticized casein (CA) and poly(vinyl alcohol) (PVA) at various ratios were prepared using the solution‐casting method. The prepared blend solutions were cast onto polystyrene petri plates and bend films were obtained. The characterization of films was performed using Fourier transform infrared spectroscopy, tensile testing, thermogravimetric analysis, contact angle measurements and water vapour permeability. According to spectroscopic analysis, there were interactions between the CA and PVA molecules. The tensile test results showed that the tensile strength of CA increased with increasing PVA content. The flexibility of plasticized CA film increased with the incorporation of PVA. The thermal stability and water vapour barrier properties of plasticized CA improved on blending with PVA. As a result, it was seen that blend films were successfully produced using plasticized CA and PVA with potential for use in biodegradable packaging applications. © 2019 Society of Chemical Industry

Poly(vinyl alcohol)–lignin blended resin for cellulose‐based composites

ABSTRACTWood has limitations in strength because of its biostructural defects, including vessels. To overcome this limitation, composite materials can be innovated by breaking wood down into cellulose and lignin and reassembling them for bio‐originating strong structural materials. In this study, an ecofriendly resin was developed that was suitable for cellulose‐based composites. To overcome the low dimensional stability of lignin and to increase its interactions with cellulose, it was blended with poly(vinyl alcohol) (PVA). The PVA–lignin resin was characterized with scanning electron microscopy, Fourier transform infrared spectroscopy, thermal analysis, mechanical tensile testing, and lap‐shear joint testing. The adhesion properties of the PVA–lignin resin increased with increasing PVA content. PVA played the role of synthetic polymer and that of linker between the cellulose and lignin, like hemicellulose does in wood. The PVA–lignin resin exhibited a high miscibility, mechanical toughness, and good adhesion properties for nanocellulose composites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46655.

Biodegradable PHBH/PVA blend nanofibers: Fabrication, characterization, in vitro degradation, and in vitro biocompatibility

Electrospinning was used to fabricate the different ratio of poly [(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] (PHBH)/Poly (vinyl alcohol) (PVA) blend nanofibers. These nanofibers of ratio PHBH/PVA 100/0, 90/10, 70/30, and 50/50 were prepared by using HFIP as solvent. Mixed solvent of HFIP/water was used to prepare for PHBH/PVA 30/70, 10/90 and water was used for pure PVA. The characteristic of morphology, thermal properties, miscibility, wettability, water absorption, and enzymatic biodegradable behaviour of these blend nanofibers have been investigated. The result indicated that PHBH/PVA blend nanofibers are immiscibility in the crystalline phase from DSC analysis with two peaks appear in 137 °C and 230 °C in the blend nanofibers. WAXD pattern of the blend nanofiber also exhibited the decrease of PHBH crystalline intensity with the increase of PVA content. However, FTIR spectra of blend nanofiber displayed the shift of hydroxyl and carbonyl stretching band which indicates the intermolecular interaction in amorphous phase. The water contact angle values increased with the increase of PVA content more than 30%. These showed the surface of blend nanofibers were hydrophobic since WCA value was more than 90°. The increase of WCA value is due to surface morphological change that is the decrease of fiber diameter. Nevertheless, blend nanofibers of PHBH/PVA of 70/30 exhibited the high water absorption more than 350% from initial weight. SEM-photograph of samples after immersing in the water showed that structure of nanofiber did not change in blend ratio of more over 50% PHBH content. These nanofibers of pure PHBH and ratio PHBH/PVA of 90/10, 70/30, and 50/50 will expect to be useful material to have the biocompatibility with cell attachment. In vitro enzymatic biodegradable resulted that degradation rate of blend nanofiber can be greatly improved by ratio of PVA polymer. NIH3T3 cells attached and proliferated well on pure PHBH nanofiber. However, blend nanofibers with PVA-rich content inhibited growth of the NIH3T3 cells.

Affect the Cross Linking Degree and Polymer Composition on the Mechanical Properties of Poly (vinyl alcohol)/ Pullu-lan Films

In this study Cross-linked PVA/Pullulan film was prepared. Cross-linking reaction done by addi-tion of gluteraldehyde at different reaction time (10,30and 60) min. Chemical interaction, me-chanical, thermal properties, water solubility and film morphology was studied for cross-linked PVA/Pullulan, PVA and Pullulan only. Thus FTIR investigated formation of hydrogen bonding between pullulan and PVA with (GA). Tensile strength, tensile modulus and elongation (%) at break for PVA/Pullulan film was improved with addition of (GA) as the reaction time proceed equivalent with increasing PVA content

Reactive toughening of urea–formaldehyde resin with poly(vinyl alcohol) by formation of interpenetrating networks

A series of urea–formaldehyde/poly(vinyl alcohol) (UF/PVA) blends were prepared via in situ polymerization. During the synthesis process, intra‐ and intermolecular acetalization of PVA occurred, along with the addition and condensation reactions between urea and formaldehyde, resulting in the formation of UF/PVA interpenetrating networks. With the increase of PVA content, the curing temperature shifted to higher temperatures and the activation energy (E) increased, suggesting that it was more difficult for the blends to cure. UF/PVA blends showed high storage modulus and only one broad tan δ peak, indicating that the stiffness was enhanced and the phase separation was limited at the chain segmental level. By the introduction of PVA, the elongation at break, impact strength, KIC value, and roughness of the fracture surface increased obviously, while the tensile strength can still maintain at a high level. Due to the forced compatibilization of the two components, homogeneous interpenetrating UF/PVA networks can form and thus the toughness of the blends was enhanced. POLYM. ENG. SCI., 58:2031–2038, 2018. © 2018 Society of Plastics Engineers

Curing of Natural Rubber/Polyvinyl Alcohol Blends Using Glutaraldehyde

According to our previous work, a novel method to vulcanize natural rubber (NR) at low temperature (below 50 °C) has been introduced using Glutaraldehyde (GA) as a curing agent. The mechanical property of GA cured NR was found to be low. It can be improved by blending NR with suitable thermoplastics. The main objective of this work is to improve the mechanical properties of this cured system. Effect of blend composition of Natural Rubber/Polyvinyl Alcohol (NR/PVA) on the properties is investigated. It is found that the mechanical properties increased with increasing PVA content. The results suggested that the blend with NR/PVA (90/10) is the most appropriate combination among the other blend compositions, which exhibits better mechanical properties. The blend NR/PVA cured using the new vulcanization technique has also been compared with cured NR without PVA and Thailand Industrial Standard (TIS) for making rubber flooring sheet. Furthermore, the resulting materials from this technique has been tried to apply on the surface of cement using energy from sunlight (∼40 °C). It is seen that, cured NR/PVA blends provide a good tacking and forming on the substrate materials. Processing at low temperature and cost effectiveness are the main advantages of this investigation. Therefore, it can be effectively applied for various industrial applications.

High performance extrusion blown starch/polyvinyl alcohol/clay nanocomposite films

Starch/polyvinyl alcohol (PVA)/clay nanocomposite films with high mechanical and barrier properties were prepared by extrusion blowing. Based on the starch/clay matrix, the effects of PVA content on the starch/PVA/clay nanocomposite films were investigated. Appropriate preparation conditions were determined by the rheological behavior of the blends. X-ray diffraction and transmission electron microscopy results demonstrated that the starch/PVA/clay nanocomposite films exhibited intercalated structures and the extent of intercalation increased with increasing PVA content. FTIR spectra showed that the molecular interactions were enhanced in the starch/PVA/clay films with higher PVA content. Dynamic mechanical analysis revealed partial miscibility between the starch and PVA in the films and the compatibility was improved when the PVA content was 50%. The maximum tensile strength and elongation at break for the starch/PVA/clay nanocomposite films were 30.18 MPa and 224.40%, respectively. The oxygen permeability of the starch/PVA/clay film with 50% PVA was dramatically decreased by about 210 times compared with that of a starch/clay film. A continuous phase inversion mechanism was proposed to explain the performance improvement of the starch/PVA/clay nanocomposite films. The starch/PVA/clay nanocomposite film is a promising material for high barrier food packaging.

Preparation and Characterizations of Zeolite – Filled Natural Rubber/Poly(vinyl alcohol) Semi–IPN Membranes

Semi–interpenetrating polymer network (semi–IPN) of natural rubber (NR) and crosslinked poly(vinyl alcohol) (PVA) was composited with zeolite 4A to form a mixed matrix (MM) membrane. PVA was crosslinked with sulfosuccinic acid (SSA) in the immediate presence of NR and zeolite. FT–IR spectroscopy confirmed the crosslinking of PVA in the MM membrane. Swelling measurements were carried out in both water and absolute ethanol. The degrees of swelling in both water and ethanol increased with increasing PVA content in the membranes, however they were found to decline upon increasing zeolite content more than 10 %w/w. The mechanical properties of the MM membranes were investigated by tensile testing. It was observed that the modulus increased with increasing zeolite content in membranes but the elongation at break was found to decrease. The thermal degradation of the MM membranes was studies using thermal gravimetry (TG). The MM membranes showed higher thermal stability compared with NR/PVA membrane due to the incorporation of zeolite. The dispersion of zeolite particles in the MM membrane was observed by scanning electron microscopy (SEM) analysis which showed a well dispersing of zeolite particles in the semi–IPN matrix. The sorption selectivities of MM membranes were enhanced with zeolite content especially, at low water concentration of ethanol–water mixtures. However the sorption selectivities of MM membranes decreased when water content in the liquid mixtures increased.

FORMULATION AND EVALUATION OF A CHITOSAN-PVA-GELLAN INSULIN IMPLANT

Objective: The purpose of this study was to ascertain the applicability of degradable materials for fabrication of an insulin release system.Methods: Insulin implants were prepared by using poly (vinyl alcohol) (PVA), gellan and chitosan by solution casting method. The prepared implants were evaluated for swellability, content uniformity, potency and purity of insulin in implants, scanning electron microscopy studies, in vitro release studies, in vitro degradation studies using lysozyme, stability studies and circular dichroism spectroscopy.Results: The swelling degree of the implants was found to be in the range of 1.07-1.56. The diffusion coefficient of water through the implant was found to depend on the calcium chloride (CaCl2) concentration. The diffusion coefficient of insulin through the chitosan-PVA-gellan in the early stages was found to be in the range of 1.99´10-5 cm2/sec to 5.24´10-5 cm2/sec and at later stages in the range of 6.9´10-6 cm2/sec to 1.10´10-5 cm2/sec. The weight of the implants was 48±0.58 mg. The insulin content in the implants was 9.86±0.10 mg. The potency of insulin extracted from the implants was 27.11±0.75 U/mg or 95.12±2.61 % of the control insulin. The in vitro release studies showed that insulin was released completely in a period of 13-19 d depending on the composition of the implant. The increase in CaCl2 retarded the rate of insulin release whereas the increase in PVA content leads to the rapid release of insulin. The device was found to undergo significant weight loss due to enzyme mediated degradation.Conclusion: These studies provide validity for the potential utility of chitosan-PVA-gellan implant systems for the delivery of insulin. The studies also demonstrate that insulin maintained its integrity within the implant system. Implants showed the complete release of insulin in 19 d and the release of insulin from the implants depended on the amount of CaCl2.

Glycerol‐plasticized spirulina–poly(vinyl alcohol) films with improved mechanical performance

ABSTRACTSpirulina–poly(vinyl alcohol) (PVA)–glycerol (SPG) films with improved mechanical performance, especially tensile strength (TS) and the elongation at break (EAB), are fabricated by a casting method. The integrity, color, solubility, microstructure, thermal properties, tensile strength, and compatibility of the SPG films are assessed. SPG films became smooth, homogeneous, and flexible after plasticizing with glycerol. The presence of PVA and hydrogen bonding of PVA with glycerol and spirulina protein improves the water resistance of SPG films by decreasing water absorption of spirulina protein and decreasing water diffusion through the films. The amount of carbonaceous residues decreases from 31% to 14% because of the co‐pyrolysis of spirulina, PVA, and glycerol. TS increases from 2.5 to 26 Mpa and modulus from 53 to 610 Mpa with increasing PVA content. Glycerol enhances film flexibility and EAB up to 50%. Spirulina can be composited with hydrophilic polymers to fabricate compatible, processable and thermally recyclable films with desirable mechanical performance. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44842.

A Kinetics Study on the Thermal Degradation of Starch/Poly (Vinyl Alcohol) Blend

The thermal degradation of starch/poly (vinyl alcohol) (PVA) blend was studied by using TG in air atmosphere. Thermo-analytic investigations on pure starch film and starch/PVA blend film were carried out to evaluate the thermal stability and the respective activation energy of the materials. Experiments in air atmosphere and under non-isothermal and isothermal condition carried out. The Kissinger and Flynn-Wall-Ozawa methods were used to calculate the activation energy of non-isothermal degradation of starch and starch/PVA blends. The results show that these two methods were suitable and effective to describe the thermal degradation of starch and starch/PVA blends. These results are shown that starch/PVA blend was thermally less stable than pure starch and thermal stability of films decreased with increasing PVA content.