PVAc Content Research Articles

Study of miscibility of melamine-formaldehyde resin and poly(vinyl acetate) blends for use as adhesives in engineered flooring

The objective of this research was to investigate the miscibility behavior of melamine-formaldehyde (MF) resin and poly(vinyl acetate) (PVAc) blends for their use as adhesives for bonding fancy veneer and plywood in engineered flooring, by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR). Blends of various compositions of MF resin/PVAc were prepared. To determine and compare the effect of PVAc content, blends with PVAc to MF resin weight ratios of 0, 30, 50, 70 and 100% were prepared. These blends displayed a single cure temperature over the entire range of compositions indicating that this blend system was miscible in the amorphous phase due to the formation of hydrogen bonding between the amine groups of the MF resin and the carbonyl groups of PVAc.

Initial tack and viscoelastic properties of MF/PVAc hybrid resins used as adhesives for composite flooring materials

The initial tack and viscoelastic properties of blends of melamine–formaldehyde (MF) resin and poly(vinyl acetate) (PVAc) emulsion on decorative veneer and plywood surfaces were investigated using a texture analyzer and dynamic mechanical thermal analysis (DMTA) at room temperature with respect to the 'open time', the time delay between applying an adhesive to a surface and contacting that surface with the other material. We determined and compared the effects of PVAc content, at 0, 30, 50, 70 and 100 wt%, in blends with MF resin. As PVAc is curable at room temperature, PVAc markedly affected the initial tack, as well as DMTA results. The degree of 'tack' was determined quantitatively based on the probe tack data. As the adhesion in an engineered flooring should be achieved in 2–3 min, the acceptable tack range is between 100 and 200 g. From the DMTA results, i.e., the tan δ max values, the maximum loss modulus (E&Prime) and the rigidity (ΔE) of MF/PVAc blends at room temperature, it was found that tan δ and loss modulus (E&Prime) increased with increasing MF resin content. Moreover, the rigidities of the 70:30 and 50:50 MF/PVAc blends were higher than those of the other blends, especially in comparison with the pure 100% PVAc and 100% MF. We conclude that the initial tack correlates with the MF/PVAc blend ratio during the adhesion process at room temperature.

Effect of poly(vinyl acetate) (PVAc) on thermal behavior and mechanical properties of poly(3-hydroxybutyrate)/poly(propylene carbonate) (PHB/PPC) blends

To assess the compatibility of blends of synthetic poly(propylene carbonate) (PPC), with a natural bacterial poly(3-hydroxybutyrate) (PHB), a simple casting procedure of blend was used. poly(3-hydroxybutyrate)/poly(propylene carbonate) blends are found to be incompatible according to DSC and DMA analysis. In order to improve the compatibility and mechanical properties of PHB/PPC blends, poly(vinyl acetate) (PVAc) was added as a compatibilizer. The effects of PVAc on the thermal behavior, morphology, and mechanical properties of 70PHB/30PPC blend were investigated. The results show that the melting point and the crystallization temperature of PHB in blends decrease with the increase of PVAc content in blends, the loss factor changes from two separate peaks of 70PHB/30PPC blend to one peak of 70PHB/30PPC/12PVAc blend. It is also found that adding PVAc into 70PHB/30PPC blend can decrease the size of dispersed phase from morphology analysis. The result of tensile properties shows that PVAc can increase the tensile strength and Young’s modulus of 70PHB/30PPC blend, and both the elongation at break and the tensile toughness increase significantly with PVAc added into 70PHB/30PPC.

Miscibility and morphology in blends of poly( l-lactic acid) and poly(vinyl acetate- co-vinyl alcohol)

Poly(vinyl acetate- co-vinyl alcohol) copolymers [P(VAc- co-VA)] were prepared by acidic hydrolysis of poly(vinyl acetate) (PVAc) at various reaction time, and the degree of hydrolysis was analyzed by 13C nuclear magnetic resonance spectroscopy (NMR). Blends of poly( l-lactic acid) (PLA) and P(VAc- co-VA) were prepared by a solvent casting method using chloroform as a co-solvent. The PLA/PVAc blends exhibited a single glass transition over the entire composition range, indicating that the blends were miscible systems. On the contrary, for the blends with even 10% hydrolyzed PVAc copolymer, the phase separation and double glass transition were observed. With increasing neat PVAc contents, the heat of fusion decreased and the melting peaks shifted to lower temperature. The interaction parameter indicated negative values for up to 10% hydrolyzed samples, but positive values at more than 20% hydrolyzed one. Small angle X-ray scattering analysis revealed that the long period and the amorphous layer thickness increased with PVAc composition, suggesting that a considerable amount of PVAc component located in the interlamellar region. Polarized optical microscopy showed that the texture of spherulites became rougher on increasing the PVAc content. In the case of P(VAc- co-VA) copolymer, the intensity of polarized light decreased significantly, indicating that P(VAc- co-VA) component seemed to be expelled out of the interfibrillar regions. Scanning electron microscopy analysis revealed that the significant phase separation occurred with increasing the degree of hydrolysis. In the case of 70/30 blend of PLA and P(VAc- co-VA) with 30 mol% vinyl alcohol, the P(VAc- co-VA) copolymer formed the regular domains with a size of about 10 μm.

Miscibility and ferroelectric behavior in blends of poly(vinylidene fluoride/trifluoroethylene) and poly(vinyl acetate)

AbstractThe blend system containing a poly(vinylidene fluoride/trifluoroethylene) [P(VDF/TrFE)] copolymer (68/32 mol %) and poly(vinyl acetate) (PVAc) was miscible from the results of differential scanning calorimetry (DSC) studies that exhibit the presence of a single, composition‐dependent glass transition temperature (Tg) and a strong melting point depression for the semicrystalline P(VDF/TrFE) component. However, differences between the DSC and dielectric measurements, which showed a separate P(VDF/TrFE) Tg peak, suggests that the P(VDF/TrFE)/PVAc blends are actually partially miscible. Because of the lower dielectric constant of PVAc and the reduced sample crystallinity caused by the addition of PVAc, both the dielectric constant and the remanent polarization of the copolymer blends decrease with increasing PVAc content. The presence of a small amount of PVAc stabilized the anomalous ferroelectric behavior of ice–water‐quenched P(VDF/TrFE), and the blend portrayed normal polarization reversal behavior after adding only 1 wt % PVAc. The piezoelectric response suggests small changes with an increasing number of poling cycles. It is believed that PVAc affects the D‐E hysteresis behavior at the interface between crystalline and amorphous phases, although much work remains to be done to confirm this hypothesis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 927–935, 2003

Effect of curing temperature on the morphology of unsaturated polyester resin blended with poly(vinyl acetate)

AbstractPhase separation of unsaturated polyester/styrene (UPE/styrene) resin blended with 5 and 10 wt% of poly(vinyl acetate) (PVAc) cured at various temperatures ranging from 75°C to 150°C was studied using low angle laser light scattering (LALS) and scanning electron microscopy (SEM). For UPE/styrene resin blended with 5 wt% PVAc cured at a temperature below 90°C, a discrete phase‐separated structure was observed. As curing temperature was raised above 90°C, SEM micrographs revealed that more and more cured UPE globules fused together with increasing curing temperature. The LALS intensity profile became broader with increasing curing temperature, indicating a less discrete phase‐separated structure at a higher curing temperature. As PVAc content was increased to 10 wt%, SEM micrographs revealed a co‐continuous phase‐separated structure. The LALS intensity decayed slowly from the center of the scattering pattern to a high scattering angle without the appearance of maximum scattering peak intensity. The morphology of the cured sample did not change too much with curing temperature for UPE/styrene resin blended with 10 wt% of PVAc.

Thermal degradation kinetics of poly(vinyl chloride-co-vinyl acetate)

The kinetics of thermal degradation of three vinyl chloride-co-vinyl acetate (PVC-co-PVAc) copolymers with PVAc content of 14, 14 and 10 wt.% was investigated at various temperatures (220–250 °C) in solution. Reaction samples were analyzed by gel permeation chromatography (GPC) to obtain the molecular weight distribution (MWD). The degradation rate coefficients were determined from the time evolution of the MWDs. The energies of activation, determined from the temperature dependence of the rate coefficients, of the three copolymers were 92, 77 and 100 kJ/mol, respectively. The degradation of these copolymers was also investigated thermogravimetrically in the presence of nitrogen. The activation energies, determined from the Friedman technique, were 114, 92 and 131 kJ/mol, respectively. This indicated that the overall stability order of the copolymers remained same in both the methods. This also indicated that copolymers having the same PVAc content exhibit different stability. To our knowledge, this is the first paper that reports the activation energies, rate coefficients for the degradation of these copolymers as well as show that copolymers having the same composition degrade differently.

Crystallization behavior and mechanical properties of poly(ethylene oxide)/poly(L‐lactide)/poly(vinyl acetate) blends

Poly(vinyl acetate) (PVAc) was added to the crystalline blends of poly(ethylene oxide) (PEO) and poly(L-lactide) (PLLA) (40/60) of higher molecular weights, whereas diblock and triblock poly(ethylene glycol)–poly(L-lactide) copolymers were added to the same blend of moderate molecular weights. The crystallization rate of PLLA of the blend containing PVAc was reduced, as evidenced by X-ray diffraction measurement. A ringed spherulite morphology of PLLA was observed in the PEO/PLLA/PVAc blend, attributed to the presence of twisted lamellae, and the morphology was affected by the amount of PVAc. A steady increase in the elongation at break in the solution blend with an increase in the PVAc content was observed. The melting behavior of PLLA and PEO in the PEO/PLLA/block copolymer blends was not greatly affected by the block copolymer, and the average size of the dispersed PEO domain was not significantly changed by the block copolymer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3618–3626, 2001

Preparation and electrochemcial characteristics of plasticized polymer electrolytes based upon a P(VdF-co-HFP)/PVAc blend

Polymer electrolytes based on the mixture of the blended polymer matrix (P(VdF-co-HFP)(Kynar 2801)/poly(vinyl acetate)(PVAc)) and the liquid electrolyte(EC/PC/1M LiClO 4) were prepared by solution casting. Ionic conductivity, interfacial stability with the lithium electrode, and electrochemical stability window of the polymer electrolytes were investigated by varying the PVAc content in the matrix polymer. The ionic conductivity of the plasticized polymer electrolyte slightly decreased with the PVAc content. The ionic conductivity of the polymer electrolyte based on the Kynar 2801/PVAc (7/3, w/w) blend was 2.3×10 −3 S cm −1 at 25°C. Interfacial stability between the polymer electrolyte and the lithium electrode was enhanced by blending PVAc with the Kynar 2801. The polymer electrolyte based on the Kynar 2801/PVAc (7/3, w/w) blend was electrochemically stable up to 5.0 V.

Investigation of the phase structure of poly(3-hydroxybutyrate)/poly(vinyl acetate) blends by dielectric relaxation spectroscopy

Blends of poly(3-hydroxybutyrate) (PHB) and poly(vinyl acetate) (PVAc) were isothermally cold crystallized from homogeneous samples obtained by quenching. Dielectric relaxation spectroscopy has been used to investigate the glass–rubber relaxation characteristics and corresponding phase separation in cold-crystallized PHB/PVAc blends as a function of blend composition and crystallization conditions. All isothermally cold-crystallized blends displayed two glass–rubber relaxations corresponding to the coexisting of a mixed amorphous interlamellar phase, and a pure PVAc phase residing in interfibrillar/interspherulitic regions. No PHB relaxation was observed, indicating the absence of a pure crystal–amorphous interphase. The composition of the interlamellar phase was enriched in PVAc with increasing overall PVAc content in the blend. Lowering the crystallization temperature led to an increase in the amount of PVAc trapped in the interlamellar regions, which was consistent with kinetic control of the evolving morphology: as crystallization temperature decreased, the crystallization rate increased and the diffusion of PVAc molecules decreased. Comparison of the relaxation characteristics of interfibrillar/interspherulitic phase with those of pure PVAc indicated a much broader spectrum of local relaxation environments of PVAc in the blend, consistent with PVAc segregation across a wide range of size scales.

Crystallization behavior and mechanical properties of poly(ethylene oxide)/poly(L-lactide)/poly(vinyl acetate) blends

Poly(vinyl acetate) (PVAc) was added to the crystalline blends of poly(ethylene oxide) (PEO) and poly(L-lactide) (PLLA) (40/60) of higher molecular weights, whereas diblock and triblock poly(ethylene glycol)–poly(L-lactide) copolymers were added to the same blend of moderate molecular weights. The crystallization rate of PLLA of the blend containing PVAc was reduced, as evidenced by X-ray diffraction measurement. A ringed spherulite morphology of PLLA was observed in the PEO/PLLA/PVAc blend, attributed to the presence of twisted lamellae, and the morphology was affected by the amount of PVAc. A steady increase in the elongation at break in the solution blend with an increase in the PVAc content was observed. The melting behavior of PLLA and PEO in the PEO/PLLA/block copolymer blends was not greatly affected by the block copolymer, and the average size of the dispersed PEO domain was not significantly changed by the block copolymer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3618–3626, 2001

Crystallisation of poly(3-hydroxybutyrate)/polyvinyl acetate blends

Poly(3-hydroxybutyrate) (PHB) has been blended with poly(vinyl acetate) (PVAc) and the system has been found to be miscible over the complete composition range studied, i.e. 0–100 wt%. The blends exhibited a single glass transition temperature, which varied with composition between the limits of the two homopolymers. Positive deviation from a linear dependence of the glass transition temperature with composition was observed and a molecular interaction parameter determined. At temperatures close to the melting point, the rates of bulk crystallisation as measured by DSC were found to increase with PVAc content. This was not observed in crystallising close to the glass transition temperature, where addition of PVAc not only increased the T g but also retarded the crystallisation. Hot-stage microscopy confirmed that the spherulitic radial growth rates were reduced by the addition of PVAc, but this was not due to the lowering of the equilibrium melting point. This study also showed that the nucleation density was greater in the blends than in PHB itself. The anomalous increase in the bulk crystallisation rates has been attributed to an increase in the nucleation density produced in blending with PVAc. PHB is a bacteriological polymer and is low in impurities which can act as nuclei for crystallisation, such that few spherulites are observed in the light microscope. Blending with PVAc was considered to add impurities with a resulting increase in nucleation density in the blends.

Microvoids in unsaturated polyester resins containing poly(vinyl acetate) and composites with calcium carbonate and glass fibers

When thermoplastics is added as a low-profile additive (LPA) to an unsaturated polyester (UP) resin, microvoids are introduced and compensate for the high volume shrinkage of the resin. The characteristics and mechanisms involved in the microvoid formation of a low-shrinkage UP resin system with poly(vinyl acetate) (PVAc) as LPA were investigated in this work. Both PVAc and styrene were found to play vital roles in controlling the microvoid formation. The voids were developed from an isolated type to an interconnected type by increasing PVAc content to reach a co-continuous phase structure of UP resin and PVAc, and their sizes were significantly enlarged by increasing styrene content. The microvoid formation was also affected by the curing conditions and compositions. It was enhanced by high curing temperature, but substantially restrained by an applied external pressure. When a filler was introduced to the PVAc-containing resin or when the resin was cured with t-butyl perbenzoate (TBPB), the number of voids increased. A foaming process, i.e. the surplus-styrene nucleation and expansion in the PVAc phase during the curing process, is considered to be the major mechanism for the microvoid formation.

Miscibility of biodegradable aliphatic polyester and poly(vinyl acetate) blends

We report miscibility behavior for synthetic biodegradable aliphatic polyester (BDP) and poly(vinyl acetate) (PVAc) blends by investigating their thermal, rheological, and mechanical properties. Two separate glass transition temperature peaks for the BDP/PVAc blends proved that these blend systems are immiscible. From the rheological measurement, the shear viscosity as a function of shear rate is observed to increase with increasing PVAc content in BDP/PVAc blends, since PVAc has a relatively high molecular weight compared to BDP. Moreover, BDP blends with 10 wt % PVAc have excellent mechanical properties. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1348–1352, 2000

Poly(hydroxyether of bisphenol A)/poly(vinyl acetate) blends:In situ polymerization preparation, morphology, and properties

The blends of poly(hydroxyether of bisphenol A) (phenoxy) and poly(vinyl acetate) (PVAc) were prepared through in situ polymerization, i.e., the melt polymerization of diglycidy ether of bisphenol A (DGEBA) and bisphenol A in the presence of PVAc. The polymerization reaction started from the initial homogeneous ternary mixture of PVAc/DGEBA/bisphenol A; the phase separation induced by reaction occurred as the polymerization proceeded. The phenoxy/PVAc blends with PVAc content up to 20 wt % were obtained and were further characterized by the solubility, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and scanning electronic microscopy (SEM). The results indicate that no intercomponent reaction occurred during the in situ polymerization. All the blends display separate glass transition temperatures (Tg's); the very fine phase-separated morphology was obtained by this polymerization blending method. Mechanical tests show that the prepared blends exhibited substantial improvement of mechanical properties, especially in impact strength, which could be ascribed to the formation of the fine phase-separation morphology during in situ polymerization. The thermogravity analysis (TGA) of the blends showed that the thermal stability of the PVAc-rich phases in the blends was enhanced in comparison to the pure PVAc due to the synergistic contribution of the two phases in energy transportation. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2329–2338, 1999

Phase separation of unsaturated polyester resin blended with poly(vinyl acetate)

The behavior of phase separation during the curing reaction of unsaturated polyester (UPE) resin in the presence of low profile additive, that is, poly(vinyl acetate) (PVAc), was studied by low-angle laser light scattering (LALS) and scanning electron microscopy (SEM). The experimental results revealed that the PVAc-rich phase was regularly dispersed in the cured styrene–UPE matrix for styrene–UPE resin blended with 5 wt % of PVAc. As the PVAc content was increased higher than 10 wt %, a cocontinuous PVAc and cured styrene–UPE phase was observed for the cured systems. The LALS observations were carried out in situ at a curing temperature of 100°C; thus, the effect of the rate of exothermic heat released from curing reaction on the morphology of curing system was investigated and reported in this work. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2413–2428, 1999

Diffusion behaviour of 22Na in the poly(ethylene oxide)–poly(vinyl acetate) system

In this work the diffusion of sodium-22 was studied in the PEO–PVAc films by means of an autoradiography technique. It is found that the addition of the amorphous PVAc (up to 20 mol.%) increases the effective diffusion coefficients of 22Na more than one order of magnitude at ambient temperatures. The enhancement is accompanied by a decrease in activation energy. The addition of PVAc increases the disordered amorphous surface layer of the spherulites where the diffusion process occurs at an enhanced rate. With further increasing of PVAc content the distance between large PEO spherulites increases, consequently the share of disordered amorphous regions decreases and the diffusion length of migration changes. It leads to decrease in the diffusion coefficients.

Isothermal crystallization kinetics and melting behavior of poly(β-hydroxybutyrate)/poly(vinyl acetate) blends

The overall isothermal crystallization kinetics and melting behavior of poly(beta-hydroxybutyrate) (PHB)/poly(vinyl acetate) (PVAc) blends were studied by using differential scanning calorimetry(DSC). The Avrami analysis indicates that the addition of PVAc into PHB results in the decrease in the overall crystallization rate of the PHB phase, but does not affect PHB's nucleation mechanism and geometry of crystal growth. The activation energy of the overall process of crystallization increases with the increasing PVAc content in the blends. The phenomenon of multiple melting endotherms is observed, which is caused by melting and recrystallization during the DSC heating run. (C) 1998 Elsevier Science Ltd. All rights reserved.

Spiral Crystal Growth in Blends of Poly(vinylidene fluoride) and Poly(vinyl acetate)

Crystallization behavior and morphology development in miscible blends of poly(vinylidene fluoride) (PVDF) and poly(vinyl acetate) (PVAc) have been investigated on the basis of light scattering, optical microscopy, and atomic force microscopy (AFM). Strikingly, a spiral crystal growth was observed at the core of the spherulites in the pure PVDF as well as in its blends with PVAc. The spiral structure appears to emerge from the aggregation of microfibrils during crystallization. The AFM study revealed that the microfibrils at the core are partially aligned with their long axes parallel to the spiral axis during the initial growth stage, but the fiber axes gradually change their orientation in the perpendicular direction as the spiral wave propagates toward an outer edge. The band periodicity was found to increase with increasing amorphous PVAc content. Furthermore, the periodic distance between neighboring spiral arms increases from the core to the outer edge, and this may be ascribed to the preferential r...

Mapping phases of poly(vinyl alcohol) and poly(vinyl acetate) blends by FTIR microspectroscopy and optical fluorescence microscopy

Fluorescence optical microscopy (FOM) of poly(vinyl alcohol) (PVA) and poly(vinyl acetate) (PVAc) blends in compositions 9/1, 1/1, and 1/9 (w/w) show that these blends present phase separation in the solid state. Each domain of the solid samples was identified by FOM as PVA-richer domains by green fluorescence of fluorescein and PVAc-richer domains by the blue fluorescence of anthracene. The dimensions, shapes, and distributions of these domains were dependent on the initial composition of the polymeric mixtures in the solution. Specific interactions between both homopolymers were studied using FTIR microspectroscopy, which allowed us to obtain spectra for both PVA-richer and PVAc-richer domains. These spectra demonstrated that partial miscibility could occur only for blends with a higher PVAc content and, in these cases, we observed interchain hydrogen-bonded carbonyl groups. Fluorescence microscopy of blends with this partial miscibility exhibited small interconnected domains produced by coalescence of droplets during the polymer phase separation process. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 645–655, 1998