Physical and surface properties of aqueous solutions of polyvinyl alcohols having an n-alkylthio end group

The polyvinyl alcohols (PVAs) having a n-alkylthio end group of 10 through 16 carbon atoms were found to associate in the dilute aqueous solutions through hydrophobic interaction. From the apparent number-average molecular weight with vapor pressure osmometer, the PVAs having an n-dodecylthio and an n-hexadecylthio group at one end were calculated to associate by about five and three molecules, respectively. The aqueous solutions of the PVA having an n-dodecylthio group at one end showed much higher viscosity compared with the PVA having a hydroxyethylthio group at one end (HOCH₂CH₂S—PVA) in low concentration regions of below 10 wt % due to the association of the n-dodecyl end group. Surface tensions of the aqueous solutions of the PVAs having an n-alkylthio group at one end (n-C_nH_2n+1S—PVA) showed almost the same value, which was slightly smaller than that of HOCH₂CH₂S—PVA, at 4 and 6 of carbon atoms, lowered with an increase in the number of carbon atoms above 8, showed minimum at 12 and then increased at 16 and 18. In the emulsion polymerization of vinyl acetate, n-C_nH_2n+1S—PVAs of 10 through 18 carbon atoms acted effectively as a protective colloid.     

Relationship between electron sensitivity and chemical structures of polymers as electron beam resists. VI: Electron sensitivity of various acetalized poly(vinyl alcohol)s

Acetalized poly(vinyl alcohol)s which were synthesized from poly(vinyl alcohol) (PVA) and aldehyde or ketone were evaluated as electron beam (EB) resists, in order to investigate the relationship between EB sensitivity and chemical structures of the polymers. It was found that the acetalized PVAs were easily crosslinked by EB exposure. The main mechanism of crosslinking may be radical reaction at acetal group. The sensitivity of the acetalized PVA depended on the structure of the acetal group. Acetalized PVAs synthesized from benzaldehyde, in which the electron attracting group was substituted on the benzene ring and from linear aliphatic aldehyde having a long alkyl chain, had high sensitivity. A high sensitivity of 7.2 × 10⁻⁷ C/cm² was attained when the acetalized PVA synthesized from p-chloro-benzaldehyde was used. Acetalized PVAs synthesized from PVA and aldehyde having a cyclic structure had an excellent dry etching durability and were suitable as negative EB resists.     

Morphology-rheology relationship in hyaluronate/poly(vinyl alcohol)/borax polymer blends

In this work, we have prepared bioartificial polymer blends using hyaluronate (HA) as a biological component and poly(vinyl alcohol)-borax association (PVAs) as a synthetic component, and investigated the rheological properties as well as morphology of the blends. When plotted against the blend composition, the rheological properties showed both positive and negative deviation from the linear additive mixing rule depending on thermal history. The blend showed enhanced viscosity at the composition of 20 wt% of HA and 80 wt% of PVAs, when PVA was dissolved at high temperature. The viscosity enhancement was caused by the network formation of HA aggregates in the micrometer scale. In addition, the network structure of HA aggregates was found to be fractal with the fractal dimension of 1.7. As PVA system also forms a network structure in the nanometer scale between hydroxyl groups of PVA and borate anions, the blend system is unique in that it has network structures in both micrometer and nanometer scales in one material. On the contrary, HA formed aggregates but not any network structure in the blend of the same composition but of the negative deviation. In conclusion, we showed that HA/PVAs blend system may have diverse morphology as well as very broad spectrum of rheological properties, and could suggest that the rheology and morphology of HA/PVAs blends can be designed not only by controlling composition but also by controlling thermal and deformation history of the components.     

The role of polyvinyl alcohol in emulsion polymerization

Emulsion polymerization of styrene (St) and vinyl acetate (VAc) in the presence of conventional polyvinyl alcohol (PVA), PVA modified with a terminal alkyl group or PVA modified with a terminal thiol group (HS-PVA) was compared. Whereas stable PVAc latexes were obtained, a stable PSt latex was obtained only in the case of HS-PVA. From the adsorption isotherms of these PVAs on the surface of PVAc and PSt latex particles, as well as the grafting efficiencies of VAc and St onto HS-PVA in relation to the stability of the polymerization process, the role of PVA in the emulsion polymerization was discussed.     

Effect of emulsion polymerization conditions of vinyl acetate on the viscosity fluctuation and gelation behavior of aqueous poly(vinyl alcohol) solution

Poly(vinyl alcohol) (PVA) was prepared by emulsion polymerization of vinyl acetate (VAc) at 40, 50, and 60°C. PVAs of various molecular parameters were dissolved in water at concentrations of 3, 5, and 7% (g/dL) and aged at 30 and 60°C. The effects of the molecular weight and polymerization temperature on the viscosity fluctuation and gelation behavior of aqueous PVA solutions were investigated. Viscosity was increased with increasing molecular weight when other parameters were held the same. PVA of superior molecular regularity due to the lower polymerization temperature of VAc had higher relative viscosity. Viscosity and its fluctuation of PVAs with aging time varied with the polymerization temperature of the precursors, concentration of the aqueous solutions, and aging time. For PVA with a number‐average degree of polymerization of 2800 prepared from poly(vinyl acetate) polymerized at 40°C, a sharp increase in viscosity was observed after 500 min of aging at a concentration of 7%. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1897–1902, 2001     

Water stability of high‐molecular‐weight (HMW) syndiotacticity‐rich poly(vinyl alcohol) (PVA)/HMW atactic PVA/iodine complex blend films

To precisely identify the effect of blend ratios of syndiotacticity‐rich poly(vinyl alcohol) (s‐PVA)/atactic PVA (a‐PVA) on the water stability of s‐PVA/a‐PVA/iodine complex blend films, we prepared two PVAs with similar number‐averaged degrees of polymerization of 4000 and degrees of saponification of 99.9% and with different syndiotactic diad contents of 58.5 and 53.5%, respectively. The desorption behavior of iodine in s‐PVA/a‐PVA/iodine complex films in water was investigated in terms of the solubility of s‐PVA/a‐PVA blend films in water. The degree of solubility of s‐PVA/a‐PVA blend films with s‐PVA content over 50% in water at 70°C was limited to about 10–20%, whereas that of s‐PVA/a‐PVA blend films with s‐PVA content of 10% was 85% under the same conditions. The degree of iodine desorption of complex blend films decreased with increasing s‐PVA content. The degree of iodine desorption of s‐PVA/a‐PVA drawn film with s‐PVA content of 90% was limited to 7%, regardless of the soaking temperature from 30 to 70°C. The desorption of iodine in water was strongly affected by the dissolution of blends. Moreover, the stability of iodine in the drawn s‐PVA/a‐PVA/iodine blend films in hot water was far superior to that of the undrawn film. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1435–1439, 2004     

接枝-氧化-酯化淀粉浆料的制备

以H2O2／NaHSO3为引发剂,水为分散介质,玉米淀粉与醋酸乙烯酯接枝聚合后再经氧化酯交换反应制备了淀粉浆料．经IR光谱确认了接枝共聚物。研究了工艺条件对接枝参数的影响,确定了较佳的制备工艺：ω（H2O2／NaHSO3）=1：3．引发剂为0．40％,接枝反应温度为35℃,接枝反应时间为2h。此浆料80％替代PVA用于T／C80／2013．1×13．1433×299160经纱上浆,织机效率高达90％．具有很好的经济效益和环境效益。     

Plasma treatment for enhancing mechanical and thermal properties of biodegradable PVA/starch blends

Two series of biodegradaable polyvinyl alcohol (PVA)/starch blends, i.e., PVA with/without plasma treatment (PP/P series), were produced by single‐screw extruder. The influences of plasma pretreatment and PVA content on the tensile properties, thermal behaviors, melt flow index, and biodegradability of blends were investigated. PVA pretreated by plasma (PPVA) reacted with glycerol was found not only to mechanically strengthen the PPVA/starch blend but also to improve the compatibility of PPVA and starch. Compared with PVA/starch blends, the melt flow indices of PPVA/starch blends were improved significantly by 200–300% and their tensile strength also increased two‐to‐three‐fold. Thermogravimetry analysis (TGA) showed that the thermal stability of PPVA/starch (85/300g) blend was better than PVA/starch blend at processing temperature and outperformed than PVA and starch at high temperature. Both the PPVA/starch and PVA/starch blends finished biodegradation within 9–10 weeks in soil burial tests. The esterification reaction of PPVA and glycerol was characterized by FTIR spectroscopic measurement and TGA test. The morphologic evolutions of the blend during biodegradation were investigated carefully by scanning electron microscope (SEM) imaging. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of magnesium chloride hexahydrate on thermal and mechanical properties of starch/PVA films

Starch/poly(vinyl alcohol) (PVA) blend films were prepared from the aqueous solutions containing starch, PVA and magnesium chloride hexahydrate (MgCl₂.6H₂O). The interaction between MgCl₂.6H₂O and starch/PVA was studied by Fourier transform infrared spectroscopy. The plasticising effect of MgCl₂.6H₂O on starch/PVA film was studied by scanning electron microscopy (SEM), X-ray diffraction, thermogravimetric analysis, dynamic mechanical analysis and tensile testing respectively. The water content of starch/PVA films increased with the content of MgCl₂.6H₂O. The absorbed water can act as the plasticiser for starch/PVA film. The crystals of starch and PVA were destroyed, and the crystallinity of starch/PVA film decreased with the plasticising effect of MgCl₂.6H₂O and water. SEM micrographs showed that the compatibility between starch and PVA improved with the addition of MgCl₂.6H₂O. The toughness of starch/PVA film increased with the content of MgCl₂.6H₂O.     

Properties of branched and network poly(vinyl alcohols) prepared with poly(vinyl alcohol) having aldehyde groups at the chain ends

Branched and network poly(vinyl alcohols) (PVAs) were prepared with inter-acetalization of the PVA with aldehyde groups at the chain ends which was prepared by the cleavage of 1,2 glycol bonds in commercial PVA. The numbers of branches estimated from molecular weights were compared with those estimated by theory. Huggins' constant and crystallinity decreased with increasing branch number. Dissolution of branched PVAs into dimethylsulphoxide was not so easy compared with commercial PVA. The colour of branched PVA–iodine complex decreased rapidly with standing while that of commercial PVA decreased gradually. Network PVAs with Young's modulus of 1–8 MPa were prepared.     

Effect of graphene loading on thermomechanical properties of poly(vinyl alcohol)/starch blend

Polymer nanocomposites based on poly(vinyl alcohol) (PVA)/starch blend and graphene were prepared by solution mixing and casting. Glycerol was used as a plasticizer and added in the starch dispersion. The uniform dispersion of graphene in water was achieved by using an Ultrasonicator Probe. The composites were characterized by FTIR, tensile properties, X‐ray diffraction (XRD), thermal analysis, and FE‐SEM studies. FTIR studies indicated probable hydrogen bonding interaction between the oxygen containing groups on graphene surface and the –OH groups in PVA and starch. Mechanical properties results showed that the optimum loading of graphene was 0.5 wt % in the blend. XRD studies indicated uniform dispersion of graphene in PVA/starch matrix upto 0.5 wt % loadings and further increase caused agglomeration. Thermal studies showed that the thermal stability of PVA increased and the crystallinity decreased in the presence of starch and graphene. FE‐SEM studies showed that incorporation of graphene increased the ductility of the composites. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41827.     

Citric acid crosslinking of poly(vinyl alcohol)/starch/graphene nanocomposites for superior properties

Polyvinyl(alcohol)/starch/graphene nanocomposites with enhanced properties were prepared by solution mixing and casting process with the aid of glycerol as plasticizer and citric acid (CA) as crosslinker. The dispersion of graphene in water was made by sonication prior to mixing it with PVA/starch solution. The effect of varying the concentration of CA crosslinker in PVA/starch nanocomposite with 0.5 wt% of graphene was studied in detail. The structural changes, properties and morphologies were characterized by different techniques. The FTIR results revealed that the crosslinking reaction enhanced the interaction between the hydroxyl groups in PVA and/or starch and the oxygen-containing groups present on the graphene sheets. The mechanical properties were also improved by the crosslinking reaction and reinforcing with graphene. The formation of PVA crystal from solution was interrupted to a large extent by the interface at the amorphous zone of polymers and also the crosslinks between the PVA and starch polymer chains. The total crystallinity of the system was found to decrease with increase in degree of crosslinking. There was a marked increase in the thermal stability as the blend system was crosslinked with CA. CA crosslinking produced compact bulk morphology and improved the homogeneity between PVA and starch. The results of this study illustrate that citric acid can be an effective crosslinker and/or compatibilizer in PVA/starch/graphene nanocomposites for improving properties, and for this reason it is a candidate to replace non-biodegradable plastic films in food packaging sector.     

氧化淀粉基水性胶粘剂的研究

以过硫酸钾-亚硫酸氢钠(KPS-NaHSO3)为引发剂,在木薯氧化淀粉上接枝苯乙烯(St)和丙烯酸丁酯(BA),并引入功能单体丙烯酸(AA),采用无皂聚合法合成了氧化淀粉基水性胶粘剂。考察了引发剂用量、单体与氧化淀粉配比、单体配比、功能单体用量、聚乙烯醇(PVA)用量和反应温度对胶粘剂性能的影响,并对接枝共聚物进行了红外光谱(FT-IR)表征。实验结果表明,当w(引发剂)=1.8%、m(单体)∶m(氧化淀粉)=3.0∶1、m(St)∶m(BA)=1.75∶1、w(AA)=2.0%和w(PVA)=3%～4%时,所制备的胶粘剂的综合性能最佳,其剥离强度为23.15 N/mm、拉伸强度为0.92 MPa。     

Role of the stereosequences of poly(vinyl alcohol) in the rheological properties of syndiotacticity‐rich poly(vinyl alcohol)/water solutions

Syndiotacticity‐rich poly(vinyl alcohols) (s‐PVAs) with various syndiotactic dyad (S‐dyad) contents were prepared by the copolymerization of vinyl pivalate and vinyl acetate with various monomer feed ratios, which was followed by the saponification of copoly(vinyl pivalate/vinyl acetate) to investigate the effect of the stereosequences of s‐PVA on the rheological properties of s‐PVA/water solutions. Through a series of experiments, we identified that the syndiotacticity had a profound influence on the rheological properties of s‐PVA/water solutions. Over a frequency range of 10^?1 to 10² rad/s, s‐PVAs with higher S‐dyad contents showed larger values of complex viscosity and storage modulus and more shear thinning at similar molecular weights and degrees of saponification of the polymer, suggesting that poly(vinyl alcohol) molecules were stiffer and more readily oriented as syndiotacticity increased. All the yield stresses of s‐PVA represented positive values, and s‐PVAs with higher syndiotacticity showed higher yield stresses. This suggests that as syndiotacticity increased, more pseudostructures were present in s‐PVA/water solutions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1858–1863, 2003     

Adhesion-to-fibers and film properties of etherified–oxidized cassava starch/polyvinyl alcohol blends

In our previous work, it was demonstrated that etherified–oxidized cassava starch (EOCS) showed greater adhesion and film properties than oxidized cassava starch (OCS). Therefore, the purpose of this paper is to reveal if blending EOCS with polyvinyl alcohol (PVA) could further enhance the adhesion of OCS to cotton and polylactic acid (PLA) fibers and toughen OCS film. The EOCS samples were synthesized through etherification of OCS with 3-chloro-2-hydroxypropyl sulfonic acid sodium in an aqueous medium, and were characterized by Fourier transform infrared spectroscopic technique. The apparent viscosity of cooked EOCS/PVA paste was measured, and the adhesion was evaluated by measuring the bonding forces of the blends to cotton and PLA fibers. Film properties were analyzed in terms of tensile strength, breaking elongation, bending endurance, scanning electron microscopy and X-ray diffraction. It was found that blending EOCS with PVA was able to further enhance the adhesion of OCS to both fibers and toughen OCS film. The enhancement in the adhesion and the film toughness was correlated with blending ratio of EOCS to PVA. With the decrease in the ratio, the breaking elongation and bending endurance of the blend films and bonding forces significantly increased. By increasing the degree of substitution (DS) of EOCS, the bonding forces of EOCS/PVA blends to both fibers gradually increased. In the adhesion, the positive influence performed by the ratio is more than that performed by the DS. The EOCS/PVA with a ratio of 50:50 and a DS of 0.031 could be adopted to further improve the adhesion and film toughness of OCS.

     

Effect of postcrosslinking modification with glutaraldehyde on the properties of thermoplastic starch/poly(vinyl alcohol) blend films

Thermoplastic starch (TPS)/poly(vinyl alcohol) (PVA) blend films were modified by crosslinking through soaking the films in glutaraldehyde aqueous solution and then heating in an oven. The effects of the concentration of the glutaraldehyde aqueous solution, soaking time, reaction temperature, and time on the crosslinking reaction were investigated. The moisture absorption and mechanical properties of the films were measured to characterize the influence of the crosslinking modification. It was found that the crosslinking modification significantly reduced the moisture sensitivity of the TPS/PVA blend films and increased the tensile strength and Young's modulus but decreased the elongation at break of the TPS/PVA blend films. The described method could be used for posttreating TPS/PVA‐based products to optimize their properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Properties of starch‐based blend films using citric acid as additive. II

Starch/polyvinyl alcohol (PVA) blend films were prepared by using corn starch, polyvinyl alcohol (PVA), glycerol (GL), and citric acid (CA) as additives and glutaraldehyde (GLU) as crosslinking agent for the mixing process. The additives, drying temperature, and the influence of crosslinker of films on the properties of the films were investigated. The mechanical properties, tensile strength (TS), elongation at break (% E), degree of swelling (DS), and solubility (S) of starch/PVA blend film were examined adding GL and CA as additives. At all measurement results, except for DS, the film adding CA was better than GL because hydrogen bonding at the presence of CA with hydroxyl group and carboxyl group increased the inter/intramolecular interaction between starch, PVA, and additives. CA improves the properties of starch/PVA blend film compared with GL. TS, % E, DS, and S of film adding GLU as crosslinking agent were examined. With increasing GLU contents, TS increases but % E, DS, and S value of GL‐added and CA‐added films decrease. When the film was dried at low temperature, the physical properties of the films were clearly improved because the hydrogen bonding was activated at low temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2554–2560, 2006     

Studies on compatibility of biodegradable starch/polyvinyl alcohol blends

Compatibility of starch/polyvinyl alcohol (PVA) blends, prepared by solution cast method, is dependent on the blend composition. Crystallinity of the blend, as measured by X‐ray diffraction (XRD) and differential scanning calorimeter (DSC), decreases with increase in starch content. Thermogravimetric analysis (TGA) shows that the broadness in the peak width at the degradation region increases with increase in starch content in the starch/PVA blend. Dynamic mechanical thermal analysis (DMTA) reveal that the broadness of the relaxation peaks is due to the partial compatibility of the glycerol plasticized starch/PVA blends. The tensile property decreases with increase in starch content and the 30/70 starch/PVA blend shows maximum ductility in respect to both the percentage of elongation and energy at break. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Preparation and characterization of films based on crosslinked blends of gum acacia,polyvinylalcohol, and polyvinylpyrrolidone-iodine complex

In an attempt to develop iodine-release systems based on polymeric blend for biomedical applications, our research group prepared blends of gum acacia (GA), polyvinylalcohol (PVA), and polyvinylpyrrolidone-iodine (PVP-I) complex. The blends of GA/PVA and GA/PVA/PVP-I prepared from the aqueous solutions of the polymers were crosslinked with glutaraldehyde to increase the water resistance of the films and to improve their thermal and mechanical properties. The crosslinked GA/PVA and GA/PVA/PVP-I blend films were characterized by FTIR spectroscopy, DSC, and TGA. The swelling behavior of the prepared blends was investigated and crosslinked GA/PVA blend films were found to be pH sensitive. The properties of PVP-I containing blends differed from those prepared without it probably due to the formation of an intermolecular interaction between PVP-I and the hydroxy-polymers. The results indicated that after crosslinking the blends showed improvement in water resistance, thermal, and mechanical properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Tailoring adhesive forces between poly(dimethylsiloxane) and glass substrates using poly(vinyl alcohol) primers

A thin poly(vinyl alcohol) (PVA) layer has been found to control adhesive forces between poly(dimethylsiloxane) (PDMS) and a glass substrate. Various PVAs were coated on glass substrates on top of which PDMS pre‐polymer was cast. After thermal curing, the peel strength was tested. It was found that the fundamental adhesive forces are attributed to the degree of hydrolysis (or saponification value) of the PVAs. For a PVA modified with a silanol group, strong adhesive force resulted. The range of tailoring the force with the PVAs was 16 kgf/m. The production of thin interlaminated PVA layers as primers was demonstrated. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39927.