Hydroxyl Groups Of Polyvinyl Alcohol Research Articles

Melt-processable polyvinyl alcohol/lignin composites with improved strength via synergistic plasticization of lignin

The characteristics of multi-hydroxyl structure and strong hydrogen bonding in polyvinyl alcohol (PVA) make its melting point close to its decomposition temperature, causing melt-processing difficulty. In this work, following the plasticization of small-molecule primary plasticizer acetamide, lignin was demonstrated as a green secondary plasticizer in realizing the melt processing and simultaneous reinforcement of PVA. During the plasticization process, lignin was able to combine with the hydroxyl groups of PVA, so as to destroy the hydrogen bonds and regularity of the PVA chains. The synergistic plasticization effect of lignin dramatically reduced the melting point of PVA from 185 °C to 151 °C. The thermal processing window of PVA composites was expanded from 50 °C to roughly 80 °C after introducing lignin. In contrast to acetamide, the addition of lignin significantly increased the tensile strength and Young's modulus of the composites to 71 MPa and 1.34 GPa, respectively. Meanwhile, lignin helped to hinder the migration of acetamide via hydrogen bonds. With the addition of lignin, the composites also displayed enhanced hydrophobicity and excellent UV shielding performance. The strategy of synergistic plasticization of lignin provides a feasible basis for the practical application of lignin in melt-processable PVA materials with good comprehensive properties.

High performance polyvinyl alcohol/lignin fibers with excellent mechanical and water resistance properties

To address the shortcoming of Polyvinyl alcohol (PVA) fibers for food or medical packaging materials including low mechanical strength and poor water resistance, lignin (LN) was used as raw material, acetone/H2O as solvent to self-assemble into lignin nanoparticles (LNP) by adverse solvent precipitation approach, and then PVA/LNP composite fibers with different LNP contents were fabricated successfully by wet and dry spinning. Herein, vast hydrophilic hydroxyl groups in PVA decreased owing to the hydrogen bond between LN and PVA, Especially, with only 0.5 wt% loading of LNP into the PVA/LNP fibers, the diameter was 94.4 dtex, tensile strength was 10.1 cN/dtex (1279.8 MPa), initial modulus was 94.7 cN/dtex (12.0 GPa), the crystallinity was 56.7 %, the orientation was 97.1 %, and water contact angle was 103.1°. Compared with pure PVA fibers, the tensile strength of PVA/LNP-0.5 fibers was increased by 44.2 % and the contact angle was increased 37°. This work provides novel insights into obtaining lignin-reinforced PVA composite fibers with strong mechanical properties and excellent water resistance properties, indicating the potential of the PVA/LNP fibers for food or medical packaging application.

Electrical Resistivities of PVA/Activated Carbon-Based Hydrogels

This study investigates the physical and electrical properties of the polyvinyl alcohol (PVA) hydrogel incorporated with edible Activated Carbon (AC). Three samples, namely PVA, PVA/AC 0.5, and PVA/AC 1.0 were prepared using the freeze-thaw method. The samples underwent six freeze-thaw cycles, each consisting of freezing at –25°C for 20 hours and subsequent exposure to room temperature for 4 hours. The porous network of hydrogel is attributed to the hydroxyl groups of PVA, resulting from the intermolecular cross-linking of PVA chains. The edible AC was uniformly dispersed within the hydrogel network, leading to a reduction in hydrogel pores. As a result, the electrical resistivity of PVA, PVA/AC 0.5, and PVA/AC 1.0 hydrogels measured 1052.9 ± 165.0 Ω.cm, 403.1 ± 29.2 Ω.cm, and 59.9 ± 4.7 Ω.cm, respectively. The incorporation of edible AC significantly decreased the resistivity of the hydrogel. So, this hydrogel is promising for biomedical and edible electronics applications.

Protein Adsorption, Calcium-Binding Ability, and Biocompatibility of Silver Nanoparticle-Loaded Polyvinyl Alcohol (PVA) Hydrogels Using Bone Marrow-Derived Mesenchymal Stem Cells.

Several approaches have evolved to facilitate the exploration of hydrogel systems in biomedical research. In this sense, poly(vinyl alcohol) (PVA) has been widely used in hydrogel (HG) fabrication for several therapeutic applications. The biological properties of PVA hydrogels (PVA-HGs) are highly dependent on their interaction with protein receptors and extracellular matrix (mainly calcium) deposition, for which there is not enough evidence from existing research yet. Thus, for the first time, the functional properties, like protein and mineral interactions, related to the proliferation of mesenchymal stem cells (MSCs) by silver nanoparticle (AgNP)-loaded PVA hydrogels (AgNPs-PVA-HGs) were investigated in the present study. The UV absorption spectrum and TEM microscopic results showed a maximum absorbance of synthesized AgNPs at 409 nm, with an average particle size of 14.5 ± 2.5 nm, respectively. The functional properties, such as the calcium-binding and the protein adsorption of PVA-HG, were accelerated by incorporating AgNPs; however, the swelling properties of the HGs were reduced by AgNPs, which might be due to the masking of the free functional groups (hydroxyl groups of PVA) by AgNPs. SEM images showed the presence of AgNPs with a more porous structure in the HGs. The proliferative effect of MSCs increased over culture time from day 1 to day 7, and the cell proliferative effect was upregulated by HGs with more pronounced AgNPs-PVA-HG. In addition, both HGs did not produce any significant cytotoxicity in the MSCs. The histological (bright light and H&E staining) and fluorescence microscopic images showed the presence of a cytoskeleton and the fibrillar structure of the MSCs, and the cells adhered more firmly to all HGs. More fibrillar bipolar and dense fibrillar structures were seen in the day 1 and day 7 cultures, respectively. Interestingly, the MSCs cultured on AgNPs-PVA-HG produced extracellular matrix deposition on day 7. Accordingly, the present results proved the biocompatibility of AgNPs-PVA-HG as a suitable system for culturing mammalian stem cells for regenerative tissue applications.

Facile casting preparation of hydrophilic coordinated PVA–Zn ion coatings with strong adhesion and high water tolerance

Fogging on transparent surfaces may severely influence vision. Thus, antifogging coatings are in high demand. Poly vinyl alcohol (PVA) and zinc chloride were mixed to prepare hydrophilic coatings (denoted as PVA/Zn2+ coatings) on glass substrates using the casting method with contact angles <59°. The polymer-metal complex was formed by the coordination of ZnCl2 with the hydroxyl groups of PVA. The adhesion and water resistance of the coating were improved by adjusting the mole ratio of PVA to Zn2+. A 5B adhesion grade of the optimal mole ratio of PVA to Zn2+ was determined according to the standard of the American Society of Testing Materials D3359, and the lap shear strength was 2.39 ± 0.42 MPa. The coordination between OH and Zn2+ was evidenced by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. UV–vis spectra show that the coating has a high optical transmittance (>90 %). In addition, the coating was applied on four common hydrophobic substrate surfaces to obtain hydrophilic surfaces. The antifogging performance of the coating indicates its potential application to many materials such as in transparent optical devices.

Semi‐IPN superabsorbent polymer based on itaconic acid and polyvinyl alcohol with improved gel strength and salt resistance

AbstractSemi‐interpenetrating polymer network (semi‐IPN) technology was introduced in order to improve the gel strength and salt resistance of itaconic acid (IA)‐based superabsorbent polymers (SAPs). A semi‐IPN SAP based on IA and 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS) was synthesized. Polymerization was performed using a one‐pot method in an aqueous solution in the presence of polyvinyl alcohol (PVA). The structural and thermal properties of PVA/poly(IA‐co‐AMPS) were studied using Fourier transform infrared, differential scanning calorimetry, and thermogravimetry analysis. PVA formed strong hydrogen bonds with hydrophilic functional groups in the SAP network to improve the gel strength and thermal stability of the SAP. A PVA content of 6 wt% increased the centrifuge retention capacity and absorbency under load of the SAP to 60.1 and 16.4 g/g, respectively. Owing to the less salt‐sensitive hydroxyl groups of PVA, semi‐IPN SAP showed higher absorption (up to 26.3%) in an aqueous salt solution. The resulting SAP has a very low concentration of residual monomers (167.4 ppm). Experimental results suggest that PVA/poly(IA‐co‐AMPS) is an eco‐friendly SAP with excellent absorption properties, making it suitable for application in personal care products.

Facilitating the proton conductivity of polyvinyl alcohol based proton exchange membrane by phytic acid encapsulated Zn-azolate MOF

It is important but still challenging to develop high-performance proton exchange membranes (PEMs) which should meet the following requirements: consecutive proton-conducting channels, efficient proton transfer, and excellent stability. In this study, polyvinyl alcohol (PVA) composite membranes were constructed by loading post synthetically phytic acid (PA) encapsulated Zn-MOF, denoted as PVA@PA@Zn-MOF-X (X = 0, 2, 4, 6. wt%). The novel Zn-MOF with high thermal and pH stability has been synthesized from the zinc salt and dual ligands (H2NDI: 2,7-bis(3,5-dimethyl) dipyrazol-1,4,5,8-naphthalene-tetracarboxydiimide; HBTA: 1 H-benzotriazole) which can be employed to host PA as proton carriers. Composite membranes were evaluated by microstructure, thermal stability, mechanical property, dimensional stability, proton conductivity, and so forth. It is found that the codoping of PA encapsulated Zn-MOF with suitable content is more stability of the composite membranes. Furthermore, PVA@PA@Zn-MOF-4 shows the highest proton conductivity of 1.85 × 10-2 S cm-1 at 80 oC and 90% RH with relatively lower value for ion exchange capacity (0.58 mmol g-1) among the composite membranes. This phenomenon is attributed to the consecutive hydrogen bonding networks which are composed of the carbonyl oxygen sites within Zn-MOF, phosphate groups of PA, and hydroxyl groups of PVA, enhancing the efficiency of proton transport. This is a referable strategy for designing and constructing the high-performance PEMs for fuel cells.

Physicochemical Characteristics and Antibacterial Activities of Freeze-Thawed Polyvinyl Alcohol/Andrographolide Hydrogels.

Andrographolide (AG) is one of the compounds in Andrographis paniculata, which has a high antibacterial activity. This paper reports the freeze-thaw method's use to synthesize polyvinyl alcohol (PVA) hydrogels loaded with AG and its characterization. From the morphological examination, the porosity of the PVA/AG hydrogel was found to increase with the increasing AG concentration. The swelling degree test revealed that the hydrogels' maximum swelling degrees were generally greater than 100%. The composite hydrogel with the highest fraction of andrographolide (PAG-4) showed greater weight loss than the hydrogel without AG (PAG-0). The molecular interaction between PVA and AG resulted in the narrowing of the band attributed to the O-H and C=O stretching bonds and the emergence of an amorphous domain in the composite hydrogels. The loading of AG disrupted the formation of hydroxyl groups in PVA and interrupted the cross-linking between PVA chains, which lead to the decrease of the compression strength and the crystallinity increased with increasing AG. The antibacterial activity of the composite hydrogel increased with increasing AG. The PAG-4 hydrogel had the highest antibacterial activity of 37.9 ± 4.6b %. Therefore, the PVA/AG hydrogel has the potential to be used as an antibacterial device.

Electrochromic properties of monosubstituted benzylboronic acid viologen

Synthesis of monosubstituted benzyl boronic acid viologen (mBBV) has been achieved. The boronic acid group in mBBV can form boronic ester bonds with the hydroxyl groups in polyvinyl alcohol (PVA), resulting in an all-in-one electrochromic gel. The immobilized viologen by boronic ester bonds can slow down the diffusion rate and effectively mitigate viologen dimerization, which may address the issues caused by dimerization. The optical contrasts of mBBV and mBBV-PVA reached 49.02% and 45.01%, respectively. The electrochemical and electrochromic properties obtained from the tests suggest the potential application of mBBV in the field of electrochromics.

Biomimetic “Nacre-like” Films Prepared via Layer-by-Layer Self-assembly of Mica, Polyvinyl Alcohol and Polymethyl Methacrylate

A film with “brick-and-mortar” structure was prepared by layer-by-layer (LBL) technique using polyvinyl alcohol (PVA) and polymethyl methacrylate (PMMA) as the flexible material or “mortar” and mica as the rigid material or “brick”. The film deposited on a glass slide after self-assembly cycles had a thickness of 3 µm thick and an uneven, wavy surface. The film exhibits enhanced mechanical properties, i e, the hardness and indentation modulus values could reach 6.14 and 68.41 GPa, respectively. The hardness and elastic toughness were found to be depended on three factors, i e, the ratio of PVA to mica, the number of self-assembly cycles, and the pretreatment method of the mica suspension. The self-assembly process was driven by formation of the hydrogen bonds between the silanol groups of mica and the hydroxyl groups of PVA and carbonyl groups of PMMA.

Anti-fouling nanofiltration membranes based on macromolecule crosslinked polyvinyl alcohol

Nanofiltration membranes with excellent anti-fouling properties were fabricated through a green surface crosslink method. Poly (styrene-maleic anhydride) (SMA) blended polyethersulfone (PES) membrane was used as a support. The SMA in the PES support served as a macromolecular crosslinker. After coating of polyvinyl alcohol (PVA) on the surface of the SMA-PES support, a PVA selective layer with gradient cross-linked structure was formed, through the esterification between the anhydride groups in SMA and the hydroxyl groups in PVA. This process adopts a full-water fabrication strategy without secondary pollution. The gradiently cross-linked PVA/SMA-PES membrane, with molecular weight cut-off (MWCO) about 600 Da and permeance around 10-12 L/(m2·h·bar), exhibited good dye/salts separation performance. In the filtration of a mixed solution of Congo Red (CR) and calcium chloride (CaCl2), the membrane rejected 98% CR and only had 10% rejection of CaCl2. In addition, this membrane processed an excellent anti-fouling property. In the BSA fouling test, the pure water flux recovery ratio (FRR) was 99%. It is expected that the PVA/SMA-PES membrane can be used in organic desalination.

Engineering of H‐Bonding Interactions in PVA/g‐C3N4 Hybrids for Enhanced Structural, Thermal, and Mechanical Properties: Toward Water‐Responsive Shape Memory Nanocomposites

AbstractNew water‐triggered shape memory nanocomposites are developed by incorporating graphitic carbon nitride nanosheets (g‐C3N4) in polyvinyl alcohol (PVA) films. The findings demonstrate that the water‐triggered shape memory effect of PVA‐filled g‐C3N4 nanocomposites (PVA/g‐C3N4) is largely enhanced via the establishment of strong H‐bonding interactions between the uncondensed amine groups of g‐C3N4 and hydroxyl groups of PVA (–OH) which induce supplementary physically cross‐linked sites in the formed nanocomposites. Additionally, the designed PVA/g‐C3N4 nanocomposites reveal the achievement of improved physicochemical properties including thermal and mechanical characteristics compared to the neat PVA. Tensile testing displays a significant increment of tensile strength (by 58%) along with an increment of the Young's modulus (by 357%), owing to the existing of noncovalent interactions in the form of H‐bonds established between the PVA matrix and g‐C3N4 functional groups. Furthermore, a shape memory mechanism is suggested to highlight the water‐triggered shape memory behaviors of the PVA/g‐C3N4 nanocomposites. The obtained results are very propitious in terms of plotting and manufacturing g‐C3N4‐based nanocomposites with enhanced mechanical, thermal, and swelling features, providing a framework for designing g‐C3N4‐derived shape memory polymers (gSMP) toward better comprehension of the shape recovery mechanism in water‐triggered gSMP nanocomposites.

Revealing the enhanced structural recovery and gelation mechanisms of cation-induced cellulose nanofibrils composite hydrogels

In this study, we fabricate physically dual-crosslinked cellulose-based hydrogels by varying coordination bonding effects with the addition of either divalent or trivalent metal cations. The first crosslinked network is created by metal-carboxylate coordination bonds between the cellulose nanofibrils that have abundant carboxyl groups and the metal cations. The second crosslinked network is formed by the reaction of tetra-functional borate ion complex and the hydroxyl groups in polyvinyl alcohol. These physically dual-crosslinked networks are strongly interwoven by non-sacrificial hydrogen bonds, this dual-crosslinked network leads to enhanced recovery characteristics in the resulting hydrogels. We use three interval thixotropic testing to investigate the deformation and recovery behaviors of the hydrogels and plot their structural deformation parameters in phase diagrams to understand the underlying complexity of energy dissipation and viscoelastic dynamics of the dual-crosslinked hydrogels.

Obtaining a copolymer of polyhexamethylene guanidine hydrochloride and polyvinyl alcohol

The possibility of obtaining a polymer gel based on polyhexamethylene guanidine hydrochloride and polyvinyl alcohol under conditions of acid catalysis is considered. It was shown that the use of formaldehyde as a crosslinking agent leads to the formation of methylene bridges between the hydroxyl groups of polyvinyl alcohol and the amino groups of polyhexamethylene guanidine hydrochloride. The study of samples obtained by IR spectroscopy revealed the presence of corresponding signals of functional groups at 2780 cm-1 (isolated methylene group between nitrogen and oxygen atoms) and 1580 cm-1 (characteristic band of the guanidine group).

Thermal Properties of Surface-Modified and Cross-Linked Boron Nitride/Polyethylene Glycol Composite as Phase Change Material

A thermally conductive phase change material (PCM) was fabricated using polyethylene glycol (PEG) and boron nitride (BN). However, the interfacial adhesion between the BN and the PEG was poor, hindering efficient heat conduction. Grafting polyvinyl alcohol (PVA) onto the surface of BN and cross-linking due to hydrogen bonding between the hydroxyl groups in PVA and oxygen atoms in PEG improved the wettability of fillers. By employing this strategy, we achieved a thermal conductivity value of 0.89 W/mK, a 286% improvement compared to the thermal conductivity of the pristine PEG (0.23 W/mK). Although the latent heat of composites decreased due to the mobility of the polymer chain, the value was still reasonable for PCM applications.

Improvement in the dispersion stability of iron oxide nanoparticles in highly concentrated brine solution using encapsulation with polymer-polymer crosslinked shells

In this study, the dispersion stability of superparamagnetic iron oxide nanoparticles (IONPs) under high salinity was investigated. In our previous study, the stable dispersion of IONPs in 5 wt% NaCl solution was achieved under neutral and basic conditions through the functionalization of IONPs using sulfonated phenolic resin (SPR). However, under acidic conditions, the SPR shell dissociated from the IONP surface, resulting in the loss of dispersion stability. To overcome this limitation, crosslinking with polyvinyl alcohol (PVA) was implemented. The sulfonate groups in the SPR and hydroxyl groups in PVA can form a bond by removing water and consequently a crosslinked structure is formed between SPR and PVA. The stability of the dispersion was evaluated using visual observation of sedimentation and size measurements of the sample for a week. It was found that the dispersion was highly stable in brine, containing up to 10 wt% NaCl, at pH 4. The shell/core structure of the highly crosslinked SPR-PVA was verified using EDS mapping of the S elements in the SPR-IONP sample. The change in the shell structure through the crosslink reaction was characterized using thermogravimetric analysis and Fourier transform infrared spectroscopy.

Development and Characterization of Membranes with PVA Containing Silver Particles: A Study of the Addition and Stability

Developing technologies for the reduction of biofouling and enhancement of membrane functionality and durability are challenging but critical for the advancement of water purification processes. Silver (Ag) is often used in the process of purification due to its anti-fouling properties; however, the leaching of this metal from a filtration membrane significantly reduces its effectiveness. Our study was designed to integrate the positive characteristics of poly vinyl alcohol (PVA) with the controlled incorporation of nano-scale silver ions across the membrane. This approach was designed with three goals in mind: (1) to improve antifouling activity; (2) to prevent leaching of the metal; and (3) to extend the durability of the functionalized membrane. The fabrication method we used was a modified version of manual coating in combination with sufficient pressure to ensure impregnation and proper blending of PVA with cellulose acetate. We then used the spin coater to enhance the cross-linking reaction, which improved membrane durability. Our results indicate that PVA acts as a reducing agent of Ag+ to Ag0 using X-ray photoelectron spectroscopy analysis and demonstrate that the metal retention was increased by more than 90% using PVA in combination with ultraviolet-photo-irradiated Ag+ reduced to Ag0. The Ag+ ions have sp hybrid orbitals, which accept lone pairs of electrons from a hydroxyl oxygen atom, and the covalent binding of silver to the hydroxyl groups of PVA enhanced retention. In fact, membranes with reduced Ag displayed a more effective attachment of Ag and a more efficient eradication of E. coli growth. Compared to pristine membranes, bovine serum albumin (BSA) flux increased by 8% after the initial addition of Ag and by 17% following ultraviolet irradiation and reduction of Ag, whereas BSA rejection increased by 10% and 11%, respectively. The implementation of this hybrid method for modifying commercial membranes could lead to significant savings due to increased metal retention and membrane effectiveness. These enhancements would ultimately increase the membrane’s longevity and reduce the cost/benefit ratio.

Preparation and characterization of polyvinyl alcohol/sodium alginate/Pyrovatex CP composite fibers

Pyrovatex CP which was used as a flame retardant was added into polyvinyl alcohol (PVA) and sodium alginate (SA) aqueous solution. PVA/SA composite fibers modified with Pyrovatex CP (PSC) were prepared by wet spinning. It was characterized by FT-IR, SEM and TG. The results showed that Pyrovatex CP reacted with hydroxyl groups of PVA and SA. The breaking strength of PSC was slightly improved and the elongation at break of PSC increased rapidly. The flame retardancy and thermal stability of PSC were characterized by limiting oxygen index (LOI) and thermogravimetric analysis, respectively. The results showed that when Pyrovatex CP was 33 wt%, the elongation at break and LOI of PSC were 66.29% and 30.4%, respectively. The residue of the PSC at 600 °C is 27%.

Graphene oxide-driven interfacial coupling in laser 3D printed PEEK/PVA scaffolds for bone regeneration

ABSTRACTBlending Polyetheretherketone (PEEK) with Polyvinyl alcohol (PVA) is promising to obtain a composite scaffold combining the excellent biomechanical properties of PEEK and the remarkable degradability of PVA. However, the weak interfacial bonding between nonpolar PEEK and polar PVA would result in poor mechanical properties. In this study, owing to its unique amphiphilic properties, graphene oxide (GO) was employed to enhance the interfacial bonding between PEEK and PVA in PEEK/PVA scaffolds that were fabricated by laser 3D printing. On the one hand, the large π-conjugated structure of GO formed strong π-π interactions with the benzene rings in PEEK. On the other hand, the oxygen-containing groups of GO formed strong hydrogen bonds with the hydroxyl groups of PVA. As a result, the interfacial free energy between PEEK and PVA decreased from 37.4 to 29.6 mJ/m2 according to the harmonic-mean rule, and the PVA phase in PEEK matrix became much fine and uniform, indicating a reinforced interfacial bonding. Correspondingly, the strength and modulus of PEEK/PVA scaffolds increased by 97.16% and 147.06%, respectively, for a GO loading of 1%. Furthermore, the scaffolds exhibited good hydrophilicity and degradability, and promoted cell attachment and proliferation in vitro and osteogenic differentiation and bone regeneration in vivo.

Effect of boric acid on poly vinyl alcohol- tannin blend and its application as water-based wood adhesive

ABSTRACT The work presented here focusses on developing adhesive by blending tannin and polyvinyl alcohol (PVA) in water. To furthermore enhance the properties crosslinking is carried by using boric acid at varying concentrations. Presence of free hydroxyl groups in PVA and tannin acts as a site for crosslinking reaction. The empty p orbital of trivalent boron atom attracts nucleophilic hydroxyl groups of PVA and tannin, hence are expected to form crosslinks. The interaction of boric acid with the blend was confirmed by FTIR spectra studies. The acidic pH favoured the reaction and its effects were observed by increase in viscosity and glass transition temperature (Tg). Films cased with the crosslinked blend demonstrated less hydrophilic behaviour from water contact angle test also increment in pencil hardness value and stress-bearing capacity. Adhesive performance properties like wet tack and time-dependent tensile lap shear strength on softwood and hardwood specimens were evaluated. The crosslinking-enhanced cohesion by reducing the free volumes between the chains and due to this, enhancement in tensile strength on bonded wood substrates was observed. Overall, it was found that the adhesive prepared by crosslinking PVA/tannin blend with boric acid is suitable for wood adhesive application.