Modification of poly(vinyl alcohol) films by the addition of magnesium chloride hexahydrate

Poly(vinyl alcohol) (PVA) films modified with Magnesium chloride hexahydrate (MgCl₂·6H₂O) were prepared by casting method. The prepared films were characterized by X‐ray diffraction measurements (XRD), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and mechanical testing. It was found that the presence of MgCl₂·6H₂O had considerable effects on the crystallinity, thermal, and mechanical properties of PVA films. The crystallization of PVA film was interrupted and the degree of crystallinity of PVA film decreased with the addition of MgCl₂·6H₂O. The glass transition temperature of PVA film decreased with the addition of MgCl₂·6H₂O. After modifying with MgCl₂·6H₂O, PVA film became soft, with lower tensile strength and higher elongation at break. The presence of MgCl₂·6H₂O could significantly increase the moisture content of PVA films and this may be the cause of the plasticizing. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

The Effect of glycerol on the crystalline,thermal, and tensile properties of CaCl2‐doped starch/PVA films

Starch/poly(vinyl alcohol) (PVA) films with the addition of 10 wt% CaCl₂ and various content of glycerol were prepared. The effect of glycerol on the crystalline, thermal, and tensile properties of CaCl₂‐doped starch/PVA films was studied by X‐ray diffraction, thermogravimetric analysis (TGA), and tensile testing, respectively. The effect of glycerol on the miscibility of CaCl₂‐doped starch/PVA films was studied by scanning electron microscopy. The CaCl₂‐doped starch/PVA film became more homogeneous after the addition of glycerol. The addition of glycerol would increase the crystallinity of CaCl₂‐doped starch/PVA film. With the addition of 10 wt% glycerol and 10 wt% CaCl₂, the starch/PVA film showed the highest degree of crystallinity. The TGA results show that the thermal stability of CaCl₂‐doped starch/PVA film increased after the addition of glycerol. The toughness of CaCl₂‐doped starch/PVA films was enhanced with the addition of glycerol. The starch/PVA film with the addition of 10 wt% CaCl₂ and 20 wt% glycerol showed the tensile strength of 17 MPa and the elongation at break of 428%. Moreover, the water sorption of CaCl₂‐doped starch/PVA film decreased after the addition of glycerol at the low and intermediate relative humidity of 33 and 54%. POLYM. COMPOS., 37:3191–3199, 2016. © 2015 Society of Plastics Engineers     

Effect of the degree of hydrolysis and polymerisation on the melting process of thermoplastic poly(vinyl alcohol)

In this work, the thermoplastic poly(vinyl alcohol) (TPVA) blend films were efficiently prepared using pure poly(vinyl alcohol) (PVA) and caprolactam–MgCl₂ ·6H₂O via the aqueous method on the condition of achieving the melting process of PVA. The effect of the degree of polymerisation (DP) and hydrolysis (DH) of PVA on plasticisation was studied using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction, differential scanning calorimeter, and thermo gravimetric analysis. The plasticising effect increases initially and then decreases with the increase of DP owing to the destruction of hydrogen bonding and the decrease in regularity in PVA. The plasticising effect increases with the increase in DH, because the plasticiser weakens the hydrogen bonding of intro-intra molecular in PVA, which is confirmed by the shift of the –OH characteristic peak of FT-IR spectra. The thermal processing windows increase owing to the coordination effect between hydrogen bonding and crystallinity. TPVA-1799 had the largest thermal processing window (120°C) and the molten filament was extruded, which were both significant for melt spinning.     

Effects of nano‐tio2 on the performance of high‐amylose starch based antibacterial films

The purpose of this article is to investigate the effects of nano‐tianium dioxide (nano‐TiO₂) on the high‐amylose starch/polyvingl alcohol (PVA) blend films prepared by a solution casting method. The results show that at the concentration of 0.6% of nano‐TiO₂, the film demonstrated the best tensile strength at 9.53 MPa, and the elongation at break was noted as 49.50%. The optical transmittance of the film was decreased and the water resistance was improved with further increase of the concentration of nano‐TiO₂. Using the techniques of Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and field‐emission scanning electron microscopy (SEM), the molecular and the crystal structures of the films were characterized. The results indicate that the miscibility and compatibility between high‐amylose starch and PVA were increased with the addition of nano‐TiO₂ into the films due to the formation of hydrogen and C? O? Ti bonds. The antimicrobial activities of the blend films were also explored. The results show that there were inhibitory zones around the circular film disc, which is attributable to the addition of nano‐TiO₂. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42339.     

Melt processing of poly(vinyl alcohol) through adding magnesium chloride hexahydrate and ethylene glycol as a complex plasticizer

The melt processing of poly(vinyl alcohol) (PVA) was achieved using magnesium chloride hexahydrate (MgCl₂·6H₂O) and ethylene glycol as a complex plasticizer. The interaction between the complex plasticizer and PVA was studied by Fourier transform infrared spectroscopy (FT‐IR). The PVA films were characterized using X‐ray diffraction (XRD), differential scanning calorimetry, thermogravimetric analysis (TGA), scanning electron microscope, and dynamic thermomechanical analysis (DMA) techniques. The band shift of the observed peak around 3335 cm^?1 in the FT‐IR spectra indicates that the complex plasticizer MgCl₂·6H₂O and ethylene glycol could form strong interactions with PVA and thus interrupt the intermolecular and intramolecular hydrogen bonding in PVA. The XRD results show that the addition of the complex plasticizer would significantly destroy the crystallites of PVA and result to the decrease of the degree of crystallinity of PVA. The melting point was reduced from 229°C of pure PVA to around 170°C after the plasticization. The TGA studies show that with the complex plasticizer, the thermal stability of PVA is improved. PVA plasticized by 30 wt% MgCl₂·6H₂O and 10 wt% ethylene glycol shows the tensile strength of 33 MPa and the elongation at break of 362%. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

A starch‐based biodegradable film modified by nano silicon dioxide

The purpose of this work was to improve the properties of the starch/poly(vinyl alcohol) (PVA) films with nano silicon dioxide (nano SiO₂). Starch/PVA/nano‐SiO₂ biodegradable blend films were prepared by a solution casting method. The characteristics of the films were assessed by Fourier Transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X‐ray photoelectron spectroscopy (XPS). The results obtained in this study indicated that the nano‐SiO₂ particles were dispersed evenly within the starch/PVA coating and an intermolecular hydrogen bond and a strong chemical bond C? O? Si were formed in the nano‐SiO₂ and starch/PVA. That the blending of starch, PVA and nano‐SiO₂ particles led to uniform starch/PVA/nano‐SiO₂ blend films with better mechanical properties. In addition, the nano‐SiO₂ particles can improve the water resistance and light transmission of the blend films. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of copper sulfate pentahydrate on the structure and properties of poly(vinyl alcohol)/graphene oxide composite films

Poly(vinyl alcohol) (PVA)/graphene oxide (GO)/copper sulfate pentahydrate (CuSO₄·5H₂O) composite films were prepared by the solution casting method, and the effect of CuSO₄·5H₂O on the structure and properties of the PVA/GO composites was investigated. Fourier transform infrared (FTIR) analysis proved the crosslinking interaction between CuSO₄·5H₂O and the ? OH group of PVA. The crystallinity of the composite films increased first and then decreased. For the composite films, the tensile strength, Young's modulus, and yield stress values improved with increasing CuSO₄·5H₂O, whereas the elongation at break decreased compared with that of the neat PVA/GO composite film. The thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG) patterns of the PVA/GO/CuSO₄·5H₂O composite films showed that the thermal stability decreased; this was consistent with the TGA–FTIR analysis. A remarkable improvement in the oxygen‐barrier properties was achieved. The oxygen permeability coefficient was reduced by 60% compared to that of the neat PVA/GO composite film. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44135.     

Effects of co‐plasticization of acetyl tributyl citrate and glycerol on the properties of starch/PVA films

Starch/polyvinyl alcohol (PVA) nanocomposite films by film blowing process were successfully obtained. Starch (1700 g), PVA (300 g), and organically modified montmorillonite (OMMT, 200 g) were blended and plasticized with acetyl tributyl citrate (ATBC) and glycerol (GLY) at weight ratios of 0/100, 5/95, 10/90, 15/85, 20/80, and 25/75. The structural, morphology, barrier, mechanical, and thermal properties of the films, as well as molecular interactions in the nanocomposites were analyzed. The 3.98 nm d‐spacing was the highest in starch/PVA nanocomposite films plasticized with ATBC/GLY ratio of 10/90. The film with ATBC/GLY (5/95) had the lowest WVP (3.01 × 10^?10 g m^?1 s^?1 Pa^?1). The longitudinal tensile strength (TS) of starch/PVA nanocomposite films gradually increased from 4.46 to 6.81 MPa with the increase of ATBC/GLY ratios. The T_g steadily increased from 49.2°C to 55.2°C and the ΔH of the nanocomposite films decreased from 81.77 to 51.43 J/g at the presence of ATBC. The addition of ATBC into GLY plasticized starch/PVA/OMMT system enhanced the intermolecular interaction in the nanocomposites. This study proved that ATBC was an excellent compatibilizer in the preparation of starch/PVA/OMMT nanocomposite films. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42544.     

Effect of nano-SiO2 on the compatibility of PVA/RSF blend

A series of poly(vinyl alcohol) (PVA)/regenerated silk fibroin (RSF)/nano-silicon dioxide (nano-SiO₂) blend films were prepared by solution casting method, in which nano-SiO₂ was obtained via sol?Cgel process. The structure, properties, and morphology of the films related to the compatibility were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). XRD peaks of PVA/RSF/nano-SiO₂ (1.0?wt?%) blends decreased in intensity indicated that formation of PVA and RSF crystal lattices was hindered by nano-SiO₂ particles. FTIR spectroscopy analysis of PVA/RSF/nano-SiO₂ films confirmed that both Si?CO?CC linkage and hydrogen bonding were formed among PVA, RSF, and nano-SiO₂. SEM showed that there was no obvious phase separation in PVA/RSF/nano-SiO₂ (1.0?wt?%) film although small uniform blur particles can still be found. In addition, TEM showed nano-particles were well dispersed through the PVA/RSF polymer matrix. Besides, the observed shift in glass transition temperatures (T _g) and improvement in thermal properties of composite films suggested the enhanced compatibility due to interfacial bonding and intermolecular interactions. Therefore, these results indicated that the compatibility of PVA/RSF was improved effectively by the addition of nano-SiO₂.     

Simulation studies on metastable phase equilibria in the aqueous ternary systems (NaCl-MgCl2-H2O) and (KCl-MgCl2-H2O) at 308.15 K

The solubilities and densities of the aqueous metastable ternary systems (NaCl-MgCl₂-H₂O) and (KCl-MgCl₂-H₂O) at 308.15 K were determined by the isothermal evaporation method. On the basis of the experimental results, the phase diagrams for those systems were plotted. It was found that the former system belongs to the hydrate-I type with one invariant point of (NaCl + MgCl₂·6H₂O), two univariant curves, and two crystallization regions corresponding to halite (NaCl) and bischo.te (MgCl₂6H₂O); and the latter system belongs to the type of incongruent-double salts with two invariant points of (KCl + KCl·MgCl₂6H₂O) and (MgCl₂·6H₂O + KCl·MgCl₂·6H₂O), three univariant curves, and three crystallization regions corresponding to potassium chloride (KCl), carnallite (KCl·MgCl₂·6H₂O) and bischofite (MgCl₂·6H₂O). No solid solutions were found in both systems.     

Metastable equilibrium for the quaternary system containing with lithium+potassium+magnesium+chloride in aqueous solution at 323K

The metastable equilibrium of the system contained with lithium, potassium, magnesium, and chloride in aqueous system was investigated at 323 K using an isothermal evaporation method. The isothermal experimental data and physicochemical properties, such as density and refractive index of the equilibrated solution, were determined. With the experimental results, the stereo phase diagram, the projected phase diagram, the water content diagram and the physicochemical properties versus composition diagrams were constructed. The projected phase diagram consists of three invariant points, seven univariant curves and five crystallization fields corresponding to single salts potassium chloride (KCl), lithium chloride monohydrate (LiCl·H₂O), bischofite (MgCl₂·6H₂O) and two double salts lithium carnallite (LiCl·MgCl₂·7H₂O) and potassium carnallite (KCl·MgCl₂·6H₂O). Salt KCl has the largest crystallization region; it contains almost 95% of the general crystallization field.     

Effect of magnesium chloride concentrations on the properties of magnesium oxychloride cement for nano SiC composite purposes

Different magnesium oxychloride cements (MOCs) were studied with a fixed 13 moles of magnesite and 12 moles of water with different moles of magnesium chloride, MgCl₂·6H₂O from 0.5 to 1.9. Cold crushing strength, initial and final setting times, and dissolution in water were all increased with an increase in magnesium chloride. 1.5 moles of magnesium chloride showed the highest compressive strength. X-ray diffraction analysis (XRD) studies showed a gradual decrease in hydrated magnesia, Mg (OH)₂ and a gradual increase in phase 5, 5Mg(OH)₂·MgCl₂·6H₂O. Scanning electron microscopy (SEM) studies indicated that needle shaped crystals of phase 5 are responsible for the reinforcement of the matrix of these Sorel cements. The highest strength sample was used to develop a nano composite with nano particles of SiC. This composite does not require melting or firing for sintering, and there is no risk of grain growth. High content of needle shaped reinforcing crystals of phase 5 in the matrix with an increase in magnesium chloride, together with nano sizes aggregate particles of SiC provided a promising nano composite.     

Preparation of PANI–PVA composite film with good conductivity and strong mechanical property

The polyaniline (PANI)–polyvinyl alcohol (PVA) conductive composite films [doped with hydrochloride (HCl), dodecylbenzene sulphonic acid and amino sulphonic acid (NH₂SO₃H) aqueous solution] were synthesised by ‘in situ’ polymerisation, and their conductivities were compared. Among these composite films, HCl–PANI–PVA composite film possessed the highest conductivity that reached 1360?S·m^??1 [w_(PVA)?=?40%]. Meanwhile, the effects of PVA content, HCl concentration, oxidant ammonium persulphate (APS) dosage, reaction time and film drying temperature on tensile strength of the HCl–PANI–PVA composite films were studied. The tensile strength of the film was improved greatly due to effective mixture of PANI and PVA. When the PVA content was 40%, C_(HCl)?=?1.0?mol·L^??1, reaction time was 4.0?h, n_(APS)/n_(aniline)?=?1.0 and film drying temperature was 80°C, and the tensile strength of the HCl–PANI–PVA composite film reached the maximum of 60.8?MPa. At the same time, the structure of composite materials was characterised and analysed through ultraviolet spectrum and SEM.     

Magnesium chloride precipitation from mixed salt solution using 1,4-dioxan

This paper deals with the preparation of magnesium chloride hydrate from a mixed salt solution containing, besides MgCl₂, substantial quantities of undesired substances such as alkali metal chlorides and magnesium sulphate. Magnesium chloride extraction was done using dioxan. In particular, it was found that this salt precipitate as the ternary compound MgCl₂·6H₂O·C₄H₈O₂. Reaction equilibrium is reached after 40 min. It was shown that solid phase MgCl₂·6H₂O·C₄H₈O₂ conversion into MgCl₂·6H₂O is feasible by a drying carried out at constant temperature chosen in the range (70-110 °C). Physico-chemical properties of the final product are determined using XRD, complexometry, potentiometry, gravimetry and FAAS. Prepared MgCl₂·6H₂O purity is upper than 99%. Its X-ray diffractogram is impurity free.     

Preparation and characterization of LDPE/PVA blend films filled with glycerin‐plasticized polyvinyl alcohol

A series of LDPE/PVA blend films were prepared via a twin‐screw extruder, and their morphology, thermal property, oxygen and water vapor permeation, surface properties, and mechanical properties were investigated as a function of the PVA content. During the extrusion process of the blend films, glycerin improved the compatibility and processing conditions between LDPE and PVA. The melting temperature (T_m), melting enthalpy (ΔH_m), crystallinity (%), and thermal stability of the thermal decomposition temperature (T_5%) of the LDPE/PVA blend films decreased with increasing PVA content. The oxygen permeabilities of the blend films decreased from 24.0 to 11.4 cm³·cm (m²·day·atm)^?1 at 23°C. The WVTR increased from 7.8 to 15.0 g(m² day)^?1 and the water uptake increased from 0.13 to 9.31%, respectively. The mechanical properties of blend films were slightly enhanced up to 2% PVA and then decreased. The physical properties of the blend films strongly varied with the chemical structure and morphology depending on the PVA and glycerin. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41985.     

Enhancement of water barrier properties of cassava starch-based biodegradable films using silica particles

Biodegradable films are used in a variety of applications, including packaging. However, their use is limited due to their high moisture and water sensitivity. In this work, cassava starch (CS) was blended with poly(vinyl alcohol) (PVA). Silica particles (SiO₂) were incorporated to increase the hydrophobicity of the blend by intermolecular interaction through hydrogen bonding between the three components. Instead of a plasticizer or crosslinker, a small amount of triethylamine was added to eliminate residual acetate groups in PVA. The miscibility of CS and PVA phases was confirmed by smooth fracture surfaces and a single glass transition temperature. When SiO₂ content was below 5% (wt), the particles were well dispersed in a continuous phase of polymer matrix. At this loading of SiO₂, the increase in tensile strength was as high as 170% and in elongation-at-break, 250%. All loadings of SiO₂ increased thermal stability of the blend films because silanol groups on the surface of SiO₂ particles formed effective interfacial interactions with hydroxyl groups of the polymers. These interactions also prevented the ingress of water molecules, significantly increasing the hydrophobicity of the films. The water contact angle increased as high as 113° and moisture absorbency and water solubility were low. These highly hydrophobic, photodegradable, biodegradable CS/PVA/SiO₂ films show great potential as a low-cost, eco-friendly material.

     

Influence of molar ratios on properties of magnesium oxychloride cement

A parametric study has been conducted to investigate the influences of the molar ratios of MgO/MgCl₂ and H₂O/MgCl₂ on the properties of magnesium oxychloride (MOC) cement. By an integrated assessment of the experimental studies of strength development and X-ray diffractograms, together with application of the relevant phase diagram, it is recognized that the molar ratios of MgO/MgCl₂ and H₂O/MgCl₂ can significantly affect the properties of MOC cement. For a MOC cement paste possessing a dominance of 5MgO·MgCl₂·8H₂O (phase 5) crystals, the molar ratios of MgO/MgCl₂ of 11-17 and H₂O/MgCl₂ of 12-18 are found to be the most favorite ranges for design purpose. The choose of the molar ratio of H₂O/MgCl₂ is, however, largely depends on the molar ratio of MgO/MgCl₂ mainly for controlling workability of paste. Therefore, the most critical parameter to be selected in the design process is the molar ratio of MgO/MgCl₂, although the reactivity of the MgO powder is also important. Besides, the molar ratio can also be affected by the reactivity of the MgO powder to be employed. It is believed that a molar ratio of MgO/MgCl₂ of 13, the most suitable one shown in this study, can be used as a starting point in the normal practice.     

Carbothermic reduction synthesis of calcium hexaboride using PVA-calcium hexaborate mixed gels

In this study, PVA-CaB₆O₁₀·5H₂O precursor mixtures were prepared by coating the ceramic powders with PVA to synthesize CaB₆ via carbothermal reduction. Boron loss, the main problem in the synthesis of borides, was reduced by the use of metastable CaB₆O₁₀ as a transitional phase which is stable until the critical temperature ranges where the boron sub-oxides have higher volatilities. To minimize boron loss, due to the high hydrophilicity and ability to form cross-linked PVA-borate gels, PVA was used as a carbon source and carbon coating process was carried out via pyrolysis of the PVA - CaB₆O₁₀·5H₂O mixed gels. The effect of the molecular weight of PVA on the CaB₆ synthesis was also studied. Because of highly efficient interaction of CaB₆O₁₀·5H₂O with the PVA60-water solution, PVA60 was found to be the optimal carbon source. The CaB₆O₁₀·5H₂O-PVA60 composite powder was characterized by using Fourier transform infrared spectroscopy (FTIR) and the effect of molecular weight of the PVA’s on the thermal characteristics of mixed powders were analyzed by using simultaneous thermal analysis (STA). The effect of carbothermic reduction temperature and dwell time on the phase formation were examined via x-ray diffractometer (XRD) and scanning and transmission electron microscopy (SEM and TEM) techniques. The optimum synthesis conditions were determined for the formation of CaB₆ as 1450ºC for 12 h under an Argon flow by using the CaB₆O₁₀·5H₂O-PVA60 mixed precursor.     

Gelation of a new hydrogel system of atactic‐poly(vinyl alcohol)/NaCl/H2O

a‐PVA/NaCl/H₂O hydrogels have been prepared by gelation of aqueous atactic‐poly(vinyl alcohol) (a‐PVA) solutions in the presence of NaCl. The gelling temperature, melting temperature and the preservation of water of the hydrogels have been measured. The effect of the addition of NaCl to the hydrogels on gelling temperature and melting temperature is marked when the NaCl concentration is over a certain value. High NaCl concentration favours high‐melting‐point hydrogels. When the NaCl concentration is high enough (such as 11%), high‐melting‐point and white turbid opaque a‐PVA/NaCl/H₂O hydrogels can be prepared, regardless of the PVA concentration. Similarly, the low gelling temperature of a‐PVA/NaCl/H₂O solutions comes from low NaCl concentration, while high gelling temperature ranges from 50 to 70 °C when the NaCl concentration is 11%. In appearance, the types of syneresis of a‐PVA/NaCl/H₂O are χ‐type or a mixture of χ‐ and n‐types; water release of the hydrogels is slowed down by the addition of NaCl. © 2002 Society of Chemical Industry     

Blends of aliphatic polyesters. IV. Morphology,swelling behavior,and surface and bulk properties of blends from hydrophobic poly(L-lactide) and hydrophilic poly(vinyl alcohol)

Blend films were prepared from hydrophobic poly(L -lactide) (PLLA) and hydrophilic poly(vinyl alcohol) (PVA) with different PLLA contents [X_PLLA (w/w) = PLLA/(PVA + PLLA)] by solution casting and melt quenching. Their morphology, swelling behavior, and surface and bulk properties were investigated. Polarizing optical microscopy, scanning electron microscopy, differential scanning calorimetry, X-ray diffractometry, and tensile testing revealed that PLLA and PVA were phase separated in these blend films and the PLLA-rich and PVA-rich phases both formed a continuous domain in the blend film of X_PLLA = 0.5. The water absorption of the blend films was higher for the blend films of low X_PLLA values when compared at the same immersion time, and it was larger than expected from those of nonblended PLLA and PVA films. The dynamic contact angles of the blend films were linearly increased with an increase in X_PLLA. The tensile strength and Young's modulus of the dry blend films decreased with a rise in X_PLLA, but this dependence was reversed because of the large decreases in tensile strength and Young's modulus for the blend films having high X_PLLA values after immersion in water. The elongation at break was higher for the wet blend film than for the dry blend film when compared at the same X_PLLA and that of the dry and wet blend films decreased with an increase in X_PLLA. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2151–2160, 2001