PVAc Content Research Articles

Supertoughened biodegradable poly(L-lactic acid) by multiphase blends system: Crystallization, rheological and mechanical properties

To toughen brittle poly(L-lactic acid) (PLA), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) and poly(vinyl acetate) (PVAc) were introduced into PLA matrix to prepared PLA/PHBH/PVAc ternary blends. PVAc was electively located in PLA matrix and refined phase morphology owing to better miscibility of PVAc with PLA than with PHBH. Increase in PVAc content decreased the crystallization rate and the crystallinity of PLA due to the dilution effect. More importantly, prominent enhancement of flexibility and toughness of PLA was obtained by the addition of PHBH and PVAc. Elongation at the break and impact strength of ternary blend with 10 wt% PVAc were 277 % and 326 % higher than that of neat PLA. Melt viscoelasticity of PLA was improved by incorporation of PHBH and PVAc. The combination of increased toughness and high melt viscoelasticity established in PLA biodegradable blends represent properties required in a wider range of applications.

Preparation of the Heterogeneous Saponified Poly(Vinyl Alcohol)/Poly(Methyl Methacrylate-Methallyl Alcohol) Blend Film.

For the first time, poly(vinyl alcohol) (PVA)/poly(methyl methacrylate–methallyl alcohol) (P(MMA-MAA)) (9:1, 7:3, 5:5) blend films were made simultaneously using the saponification method in a heterogeneous medium from poly(vinyl acetate) (PVAc)/poly(methyl methacrylate) (PMMA) (9:1, 7:3, 5:5) blend films, respectively. The surface morphology and characteristics of the films were investigated using optical microscopy (OM), atomic force microscopy (AFM), X-ray diffractometer (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). Moreover, the effect of the PVAc content on the degree of saponification (DS) of the PVAc/PMMA films were evaluated and revealed that the obtained DS value increased with the increase in PVAc content in the PVAc/PMMA blend films. According to the OM results, the saponified films demonstrated increased surface roughness compared with the unsaponified films. The AFM images revealed morphological variation among the saponified PVAc/PMMA blend films with different mass ratios of 9:1, 7:3, and 5:5. According to the DSC and TGA results, all blend film types exhibited higher thermal property after the saponification treatment. The XRD and FTIR results confirmed the conversion of the PVAc/PMMA into PVA/P(MMA-MAA) films. Thus, our present work may give a new idea for making blend film as promising medical material with significant surface properties based on hydrophilic/hydrophobic strategy.

Miscibility, crystallization and mechanical properties of poly[(3‐hydroxybutyrate)‐co‐(4‐hydroxyvalerate)]/poly(propylene carbonate)/poly(vinyl acetate) ternary blends

AbstractA ternary blend of poly[(3‐hydroxybutyrate)‐co‐(4‐hydroxyvalerate)] (P34HB), poly(propylene carbonate) (PPC) and poly(vinyl acetate) (PVAc) was initially melt‐blended in an effort to obtain an excellent balance of mechanical performance. The effect of PVAc content on the miscibility, phase morphology, thermal behavior, isothermal melt crystallization and mechanical properties of P34HB/PPC/PVAc ternary blends was systematically investigated. Dynamic mechanical analysis indicated that P34HB and PPC were immiscible, and PVAc exhibited immiscibility with PPC. PVAc was selectively dispersed in the P34HB matrix and phase morphology was refined by reducing the interfacial tension. Moreover, the PVAc component suppressed the cold crystallization and reduced the isothermal melt crystallization rate of P34HB in the ternary blends. Unexpectedly, marked increases of 32.7% and 3025% were achieved in the tensile modulus and elongation of the ternary blend containing 20 wt% PVAc compared to neat P34HB. Meanwhile, the strength did not deteriorate. The unusual combination of high ductility, strength and modulus is of great potential for expanding the practical application of sustainable and biological polymers. © 2021 Society of Industrial Chemistry.

Pro-vitamin A carotenoids in East African highland banana and other Musa cultivars grown in Uganda.

Bananas and plantains (Musa spp.) are an important staple and food security crop in sub‐Saharan Africa. In Uganda, where the consumption of East African highland banana (EAHB) is the highest in the world, the population suffers from a high incidence of vitamin A deficiency (VAD). Since the consumption of pro‐vitamin A carotenoids (pVAC) made available through the food staple can help alleviate these ailments, we set out to identify the most suitable banana variety to use in future biofortification strategies through genetic engineering. The study focussed on eight popular Musa cultivars grown in the heart of banana farming communities and across the three major agricultural zones of Uganda. The fruit pVAC concentration varied considerably within and across the cultivars tested. These variations could not be explained by the altitude nor the geographical location where these fruits were grown. More than 50% of the total carotenoids present in EAHB cultivars was found to comprise of α‐ and β‐carotene, while the retention of these compounds following traditional processing methods was at least 70%. Storage up to 14 days postharvest improved carotenoid accumulation up to 2.4‐fold in the cultivar Nakitembe. The technical challenge for a successful biofortification approach in Uganda using genetically modified EAHB lies in guaranteeing that the fruit pVAC content will invariably provide at least 50% of the estimated average requirement for vitamin A regardless of the growing conditions.

Retention of pro-vitamin A carotenoid in composite bread baked with high quality cassava flour from yellow-fleshed cassava root

Background: As one of the most widely consumed foods, bread is one of the most important agricultural products. Bread made from high-quality cassava flour is consumed in some parts of Sub-Sahara Africa (SSA). The bread has no pro-vitamin S carotenoids (pVAC) due to the use of artificial colorants. Consequently, there is a need for the use of pVAC rich foods for bread production. Foods that are rich with pro-vitamin A carotenoids can be converted into retinol in the human body and whose bioconversion contributes to the reduction of vitamin A deficiency diseases (VAD). VAD has caused annual loss of life in SSA, especially in Nigeria. The yellow-fleshed cassava root might contribute to the reduction of this disease. The high quality yellow cassava flour (YHQCF) produced from yellow-fleshed cassava root may contribute to the pVAC composition of bread. As a result, there is a need for the evaluation of the retention of pVAC in composite bread baked with high quality cassava flour from yellow-fleshed cassava roots. Methods: The YHQCF was produced from TMS01/1368 cassava variety. The bread loaves consisted of 20% and 100% YHQCF and were produced by mixing the sugar, margarine, yeast, improver, and salt with the composite flour and YHQCF respectively, after which water was added and mixed to get the homogenous dough. The dough was proofed for 2.5 hours, kneaded, cut into shape, placed in a lubricated baking pan, and baked at 200oC for 30 min. Analyses of the pro-vitamin A (cis and trans-β carotene) and dry matter content were carried out on all the samples, including samples from the YHQCF production steps using standard methods. The samples from the YHQCF production steps were chosen and analyzed for pVAC in order to check the levels of degradation of the pVAC from the raw cassava root to using the root for flour production and the quantity of pVAC retained when 100% of the YHQCF is used for bread production compared to 20% composite. The β-carotene nutrient retention of the bread was also calculated.Results: The results demonstrated how the total pVAC content of the raw yellow-fleshed cassava root was 16.83 µg/g dry basis with 29% dry matter (DM) content. Subsequent processing by peeling, washing, grating, and dewatering into granules (56% DM) caused 48% reduction in the pVAC content which was reduced to 40% after drying and milling the dried grits into YHQCF (97% DM). Preparation of recipe for bread demonstrated how the 20% composite flour dough (61% DM) contained 0.29 µg/g db pVAC representing 1.72% retention, which was later reduced to 0.25 µg/g db pVAC or 1.49% retention after baking (62%DM). On the other hand, bread loaves baked from 100% YHQCF (67% DM) retained 0.74 µg/g db pVAC representing 4.40% of the 16.83 µg/g db pVAC in the starting raw material. Conclusions: The bread produced from 100% YHQCF may contribute to the pro-vitamin A status of bread consumers in SSA more than the 20% YHQCF composite. However, both bread samples are low in pVAC. In order to attain the required retinol equivalent level after bioconversion in the human body, consumption of other foods rich in vitamin A would be required to attain the required retinol equivalent level after bioconversion in the human body but can be enhanced if consumed with other foods rich in vitamin A.Keywords: High quality cassava flour; composite flour; Bread; Pro-vitamin A carotenoid; Nutrition

Component compatibility study of poly(dimethyl siloxane) with poly(vinyl acetate) of varying hydrolysis content: An atomistic and mesoscale simulation approach

Molecular simulations are very promising computational methods to understand miscibility of polymers, surface behavior and bulk properties of materials. In this investigation, such useful computations have been carried out on blends of hydrophobic poly(dimethyl siloxane) (PDMS) with commercially available hydrolyzed grades (0%, 86% and 100% hydrolysis) of poly(vinyl acetate) (PVAc) present in varying weight fractions. The material properties like Flory-Huggins interaction parameter (χ), blend compatibility and thermal transitions have been estimated by atomistic molecular dynamics (MD). The glass transition temperature (Tg) has been estimated for pristine polymers and their blend systems as well, which are found in line with previously reported values. However, some blend systems displayed occurrences of multiple Tg's, thereby, signifying phase separation. χ values have been estimated from atomistic simulations and compared with critical χC. Among different potential energy components, torsional energy plotted against a range of temperature (~90–350 K) showed distinct inflection points near Tg. In addition, morphology has also been predicted using Dissipative Particle Dynamics (DPD) and Mesoscopic dynamics (Mesodyn) simulations in order to visualize phase segregation and results found in accord with χ and Tg studies. Interestingly, while the atomistic MD and mesoscale simulations of short-chain systems (Mw ~2000) predicted limited miscibility, the mesoscale simulations of large chain lengths (Mw ~1,00,000) depict complete immiscibility at all blend contents and all hydrolyzed PVAc grades. The blend compatibility study using atomistic and mesoscale simulations indicates that incompatibility increases with increasing degree of hydrolysis, chain length and PVAc content. Further, simulations help screen 20 wt% PVAc (0% hydrolysis and 86% hydrolysis) or 10 wt% of PVOH (100% hydrolysis) in PDMS as an optimal formulation with improved miscibility characteristics.

Preparation of a Mini-Library of Thermo-Responsive Star (NVCL/NVP-VAc) Polymers with Tailored Properties Using a Hexafunctional Xanthate RAFT Agent.

A mini-library of star-shaped thermoresponsive polymers having six arms was prepared using a hexafunctional xanthate by reversible addition–fragmentation chain transfer (RAFT) polymerization. Star polymers with homopolymeric arms of poly(N-vinylcaprolactam) (PNVCL), copolymeric arms of poly(N-vinylcaprolactam-co-N-vinylpyrrolidone) (PNVCL-co-PNVP) and also arms of block copolymers of PNVCL-b-PVAc, (PNVCL-co-PNVP)-b-PVAc, and combinations of them changing the order of the block was achieved exploiting the R-RAFT synthetic methodology (or R-group approach), wherein the thiocarbonyl group is transferred to the polymeric chain end. Taking advantage of the RAFT benefits, the molecular weight of the star polymers was controlled (Mn = 11,880–153,400 g/mol) to yield star polymers of different sizes and lower critical solution temperature (LCST) values. Removing the xanthate group of the star polymers allowed for the introduction of specific functional groups at the ends of the star arms and resulted in an increase of the LCST values. Star PNVCL-b-PVAc diblock copolymers with PVAc contents of 5–26 mol % were prepared; the hydrophobic segment (PVAc) is located at the end of the star arms. Interestingly, when the PVAc content was 5–7 mol %, the hydrodynamic diameter (Dh) value of the aggregates formed in water was almost the same sa the Dh of the corresponding PNVCL star homopolymers. It is proposed that these star block copolymers self-assemble into single flowerlike micelles, showing great stability in aqueous solution. Star block copolymers with the PVAc hydrophobic block in the core of the star, such as PVAc-b-(PNVCL-co-PNVP), form micellar aggregates in aqueous solution with Dh values in the range from ~115 to 245 nm while maintaining a thermoresponsive behavior. Micellar aggregates of selected star polymers were used to encapsulate methotrexate (MTX) showing their potential in the temperature controlled release of this antineoplasic drug. The importance of the order in which each block constituent is introduced in the arms of the star polymers for their solution/aggregation behavior is demonstrated.

Competing Stereocomplexation and Homocrystallization of Poly(l-lactic acid)/Poly(d-lactic acid) Racemic Mixture: Effects of Miscible Blending with Other Polymers

Promoting the stereocomplexation ability of high-molecular-weight poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) is an efficient way to improve the thermal resistance of the resulting materials. Herein, we studied the competing crystallization kinetics, polymorphic crystalline structure, and lamellae structure of the PLLA/PDLA component in its miscible blends with poly(vinyl acetate) (PVAc) and proposed a method to improve the stereocomplexation ability of PLLA and PDLA through miscible blending with the other polymer. Crystallization of the PLLA/PDLA component is suppressed after the addition of PVAc, due to the dilution effect. The stereocomplexation ability of PLLA and PDLA is enhanced by blending with PVAc; this becomes more obvious at a high PVAc content (≥50 wt %) but less significant with the further increase of PLLA, PDLA molecular weights. Almost exclusive formation of SCs is achieved for PLLA and PDLA after blending with a large proportion of PVAc (e.g., 75 wt %). Incorporation of PVAc also facilitates the HC-to-SC structural reorganization upon heating. The increased chain mobility, decreased equilibrium melting point, and enhanced intermolecular interactions may account for the preferential stereocomplexation in PLLA/PDLA/PVAc blends.

Improvement of the Miscibility by Combination of Poly(3-hydroxy butyrate) PHB and Poly(propylene carbonate) PPC with Additives

A series of blends of biodegradable PHB and PPC with and without additives were prepared in different ratios by the casting method. The effect of additives on miscibility, morphology and melting of PHB and PPC blends was investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), Fourier transform infrared and wide angle X-ray diffraction (WAXD). The immiscibility between the PHB and PPC blends has been shown using DSC and POM. Acetyl triethyl citrate/polyvinyl acetate (PVAc) as plasticizer and compatibilizer was used to improve the miscibility between the PHB and PPC blends. FT-IR confirmed that the miscibility can be improved by additives, therefore the crystallinity and melting temperature of PHB is depression with increasing PVAc content, the OH group broadened and the ester band C=O shifted in blends 7, 8 and 9, due to hydrogen-bonding interaction. The peak position of C=O of blend 1, 2 and 3 remains constant without any change, i.e. PHB and PPC do not form any intact due to their incompatibility. WAXD showed reduced crystallinity and peak broadening in the patterns of the blends. Electrospun fiber of blend 9 has been manufactured and the morphology was investigated by scanning electron microscopy. Electrospun fibers are homogenous and their diameters were affected by solution concentration. It was found that the elongation at the break of electrospun fibers of PHB/PPC blends increased by adding additives.

Poly(vinyl alcohol) - poly(vinyl acetate) composite films from water systems: formation, strength-deformation characteristics, fracture

The object of investigation was thin (< 200 μm) films, formed by casting from water based mixtures of poly(vinyl alcohol) (PVA) water solution and poly(vinyl acetate) (PVAc) water suspension. Starting systems hence were suspensions of plasticized PVAc particles in PVA water solution. Systems with full range of PVAc volume fraction ϕPVAc were studied. Kinetic relationships of several parameters which characterize film formation in drying process were compared and scrutinized. It revealed that the main factor which restrains coalescence of PVAc particles in the composite is high viscosity of PVA water solution at the final stage of composite structure formation. In tensile deformation conditions PVA/PVAc systems behave as being PVA matrix composites in a whole range of PVAc content. Use of Kerner approach, based on the self-consistency idea, for the analysis of ECOMP(ϕPVAc) relation, confirms the continuity of PVA matrix

Ternary nanocomposites: Curing, morphology, and mechanical properties of epoxy/thermoplastic/organoclay systems

The influence of two organically modified montmorillonites on the curing, morphology and mechanical properties of epoxy/poly(vinyl acetate)/organoclay ternary nanocomposites was studied. The organoclays and poly(vinyl acetate) (PVAc) provoked contrary effects on the epoxy curing reaction. Ternary nanocomposites developed different morphologies depending on the PVAc content, that were similar to those observed in the epoxy/PVAc binary blends. The organoclays were only located in the epoxy phase independently of the morphology. All nanocomposites showed intercalated structures with similar clay interlayer distances. Both PVAc and organoclays lowered the Tg of the epoxy phase, the presence of clays did not influence the Tg of the PVAc phase. The addition of the organoclays to the epoxy improved stiffness but lowered ductility while the adition of PVAc improved toughness although reduced stiffness of epoxy thermoset. Ternary nanocomposites exhibited optimal properties that combine the favourable effects of the clay and the thermoplastic. POLYM. COMPOS., 37:2184–2195, 2016. © 2015 Society of Plastics Engineers

Effect of Poly(Vinyl Acetate) on Mechanical Properties and Characteristics of Poly(Lactic Acid)/Natural Rubber Blends

Natural rubber grafted with poly(vinyl acetate) copolymer (NR-g-PVAc) was synthesized by emulsion polymerization. Three graft copolymers were prepared with different PVAc contents: 1 % (G1), 5 % (G5) and 12 % (G12). Poly(lactic acid) (PLA) was melt blended with natural rubber (NR) and/or NR-g-PVAc in a twin screw extruder. The blends contained 10–20 wt% rubber. The notched Izod impact strength and tensile properties were determined from the compression molded specimens. The effect of NR mastication on the mechanical properties of the PLA/NR/NR-g-PVAc blend was evaluated. Characterization by DMTA and DSC showed an enhancement in miscibility of the PLA/NR-g-PVAc blend. The temperature of the maximum tan δ of the PLA decreased with increasing PVAc content in the graft copolymer, i.e., from 71 °C (pure PLA) to 63 °C (the blend containing 10 % G12). The increase in miscibility brought about a reduction in the rubber particle diameter. These changes were attributed to the enhancement of toughness and ductility of PLA after blending with NR-g-PVAc. Therefore, NR-g-PVAc could be used as a toughening agent of PLA and as a compatibilizer of the PLA/NR blend. NR mastication was an efficient method for increasing the toughness and ductility of the blends which depended on the blend composition and the number of mastications.

Isolation and functional characterisation of banana phytoene synthase genes as potential cisgenes

Carotenoids occur in all photosynthetic organisms where they protect photosystems from auto-oxidation, participate in photosynthetic energy transfer and are secondary metabolites. Of the more than 600 known plant carotenoids, few can be converted into vitamin A by humans and so these pro-vitamin A carotenoids (pVAC) are important in human nutrition. Phytoene synthase (PSY) is a key enzyme in the biosynthetic pathway of pVACs and plays a central role in regulating pVAC accumulation in the edible portion of crop plants. Banana is a major commercial crop and serves as a staple crop for more than 30 million people. There is natural variation in fruit pVAC content across different banana cultivars, but this is not well understood. Therefore, we isolated PSY genes from banana cultivars with relatively high (cv. Asupina) and low (cv. Cavendish) pVAC content. We provide evidence that PSY in banana is encoded by two paralogs (PSY1 and PSY2), each with a similar gene structure to homologous genes in other monocots. Further, we demonstrate that PSY2 is more highly expressed in fruit pulp compared to leaf. Functional analysis of PSY1 and PSY2 in rice callus and E. coli demonstrates that both genes encode functional enzymes, and that Asupina PSYs have approximately twice the enzymatic activity of the corresponding Cavendish PSYs. These results suggest that differences in PSY enzyme activity contribute significantly to the differences in Asupina and Cavendish fruit pVAC content. Importantly, Asupina PSY genes could potentially be used to generate new cisgenic or intragenic banana cultivars with enhanced pVAC content.

Effects of amorphous poly(vinyl acetate) on crystalline morphology of poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid)

The amorphous and crystalline phase behavior, spherulite morphology, and interactions between amorphous poly(vinyl acetate) (PVAc) and poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV) were examined using differential scanning calorimetry, polarized-light optical and scanning electron, atomic-force microscopy (DSC, POM, SEM, AFM), and small-angle X-ray scattering (SAXS). The PHBV/PVAc blend was found to be miscible with an almost linear Tg-composition relationship, indicating perfect homogeneity. Interaction parameter by melting point depression is a negative value of χ = −0.32, suggesting quite favorable interaction strength. With the intimate interaction between the amorphous PVAc and crystalline PHBV polymers, effects of PVAc on the spherulitic morphology of PHBV are quite significant. Owing to the higher Tg of PVAc (than that of PHBV), the spherulite growth rate of PHBV was depressed by increasing PVAc content in blends. Neat PHBV exhibits ring-banded spherulites when crystallized at \( {T_{\rm{c}}} = {6}0\sim {11}0^\circ {\hbox{C}} \); however, with increasing PVAc content in the blends, the temperature range at which the PHBV/PVAc blends exhibit ring-banded spherulites remains similar but the regularity increases, and the inter-ring spacing significantly decreases. In addition, the spherulite size and ring-band patterns therein are strongly dependent on Tmax (190 vs. 220 °C, respectively, for erasing prior nuclei), from which the blends were quenched to a Tc (60–110 °C) for crystallization. For PHBV/PVAc blends crystallized at the same Tc from different Tmax, higher Tmax tends to erase nuclei, leading to larger spherulites. However, such larger spherulites owing to higher Tmax are not necessarily packed with thicker lamellae.

Correlations between the morphology and the thermo-mechanical properties in poly(vinyl acetate)/epoxy thermosets

The mechanical properties of poly(vinyl acetate) (PVAc)/epoxy thermosets as a function of the PVAc content were investigated through dynamic mechanical thermal analysis from −100 to 220 °C and through tensile tests at room temperature. The morphology of the thermosets was examined by scanning electron microscopy. Cured PVAc/epoxy blends are phase separated, arising two phases that correspond to a PVAc-rich phase and to the epoxy rich-phase. The morphology evolves from nodular to inverted as the PVAc content increases. Intermediate compositions present combined morphologies, in which nodular and inverted regions are detected. The tensile properties at room temperature reveal that combined morphologies present the most ductile behaviour. The glass transition temperatures (T g) of PVAc and of epoxy phases in the blends are different from those of the neat polymers. The profile of the loss modulus (E″)–temperature curves are correlated with the change in morphology that appears increasing the PVAc content. The storage modulus (E′)–temperature curves are highly dependent on the morphology of the samples. The E′-composition dependence is predicted using several models for two-phase composites. The low-temperature β-relaxation of the epoxy is slightly modified by the presence of PVAc. The activation energies of the α and β-relaxations are not dependent on the blend morphology.

Preparation and characterizations of PVAc/P(VdF-HFP)-based polymer blend electrolytes

A novel group of polymer blend electrolytes based on the mixture of poly(vinyl acetate) (PVAc), poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP), and the lithium salt (LiClO4) are prepared by solvent casting technique. Ionic conductivity of the polymer blend electrolytes has been investigated by varying the PVAc and PVdF-HFP content in the polymer matrix. The maximum ionic conductivity has been obtained as 0.527 × 10−4 Scm−1 at 303 K for PVAc/PVdF-HFP ((25/75) wt.%)/LiClO4 (8 wt.%). The complex formations ascertained from XRD and FTIR spectroscopic techniques and the thermal behavior of the prepared samples has been performed by DSC analysis. The surface morphology and the surface roughness are studied using SEM and AFM scanning techniques respectively.

Morphology effect on the hydrothermal ageing of a thermoplastic modified epoxy thermoset

AbstractThe hydrothermal ageing of an epoxy thermoset modified with different amounts of poly(vinyl acetate), PVAc, was studied by gravimetric analysis, dynamic mechanical thermal analysis, and scanning electron microscopy. Differences in the water uptake process were observed as a function of the PVAc content, these differences were related to the morphology. Samples with nodular morphology, having spheres of thermoplastic dispersed in the epoxy matrix, showed water absorption behavior similar to neat epoxy. However, samples with inverted morphology, in which the thermoplastic formed the continuous phase, were more susceptible to water absorption; they exhibited a continued water uptake that could be described by a two‐stage diffusion model. Samples with inverted morphology showed debonding between phases after hydrothermal ageing. Different dynamic‐mechanical behavior has been found for samples that had epoxy matrix and samples with inverted morphology, both before and after hydrothermal ageing. POLYM. ENG. SCI., 47:960–968, 2007. © 2007 Society of Plastics Engineers

Miscibility and Phase Morphology of MF/PVAc Hybrid Resins for Surface Bonding of Building Interior Materials

AbstractThe objective of this research was to investigate the miscibility behavior of melamine‐formaldehyde resin and poly(vinyl acetate) blends for use as adhesives for surface materials in order to reduce formaldehyde emission. The investigation was conducted using differential scanning calorimetry, Fourier transform infrared spectroscopy, 13C CP/MAS solid state NMR, scanning electron microscope, atomic force microscopy and wide‐angle X‐ray scattering. Blends of various MF resin/PVAc weight compositions, comprising 0, 30, 50, 70 and 100%, were prepared in order to determine and compare the effect of PVAc content. 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. On the surface of the cured blends, the homogeneous dispersion of the PVAc phase in the MF resin was evident as small spherical domains and the blends were confirmed to be well combined.magnified image

Phase separation, cure kinetics, and morphology of epoxy/poly(vinyl acetate) blends

AbstractEpoxy based on diglycidyl ether of bisphenol A + 4,4′diaminodiphenylsulfone blended with poly(vinyl acetate) (PVAc) was investigated through differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and environmental scanning electron microscopy (ESEM). The influence of PVAc content on reaction induced phase separation, cure kinetics, morphology and dynamic‐mechanical properties of cured blends at 180°C is reported. Epoxy/PVAc blends (5, 10 and 15 wt % of PVAc content) are initially miscible but phase separate upon curing. DMTA α‐relaxations of cured blends agree with Tg results by DSC. The conversion‐time data revealed the cure reaction was slower in the blends than in the neat system, although the autocatalytic cure mechanism was not affected by the addition of PVAc. ESEM showed the cured epoxy/PVAc blends had different morphologies as a function of PVAc content: an inversion in morphology took place for blends containing 15 wt % PVAc. The changes in the blend morphology with PVAc content had a clear effect on the DMTA behavior. Inverted morphology blends had low storage modulus values and a high capability to dissipate energy at temperatures higher than the PVAc glass‐transition temperature, in contrast to the behavior of neat epoxy and blends with a low PVAc content. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1507–1516, 2007

Thermal stability and viscoelastic properties of MF/PVAc hybrid resins on the adhesion for engineered flooring in under heating system; ONDOL

The thermal properties of blends of melamine-formaldehyde (MF) resin and poly(vinyl acetate) (PVAc) for engineered flooring used on the Korean traditional ONDOL house floor heating system were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). The viscoelastic properties of the blends were also studied. Because MF resin is a thermosetting adhesive, the effect of MF rein was shown across all thermal behaviors. The addition of PVAc reduced the curing temperature. The TGA results showed that the DTGmax temperature and thermal stability of the blends increased with increasing PVAc content. The blends were examined in non-isothermal DSC experiments at a heating rate of 10°C/min. There was an exothermic peak in all the heating scanning curves, with each blend displaying a single curing peak temperature (Tp), intermediate between those of the two pure components and varying with the blend composition. The DMTA thermogram of MF resin showed that the storage modulus (E′) increased as the temperature was further increased as a result of the cross-linking induced by the curing reaction of the resin. E′ of MF resin increased both as a function of increasing temperature and with increasing heating rate.