Effect of boric acid and heat treatment for the formation of poly(vinyl alcohol)/iodine complex films iodinated at solution before casting

This study examined the role of boric acid and the effect of heat treatment on PVA‐iodine polarizing films prepared in the solution state before casting (IBC) of PVA/iodine/boric acid films. The films were prepared by casting aqueous solutions of 10 wt % poly(vinyl alcohol) (PVA) containing boric acid with 0, 0.1, 0.3, and 0.5 mol/l of I₂/KI aqueous solution, and I₂/KI(1 : 2) with 5 wt % of PVA. The effect of boric acid and heat treatment on the durability of the IBC PVA polarizing sheet films was investigated by UV–vis absorption spectroscopy. Boric acid was found to be essential for the complex formation in PVA/iodine solutions at relatively low I₂/KI concentrations and high temperatures. The strength of the complex peak at ∼ 600 nm in UV–vis absorption spectra increased with increasing boric acid concentration. With increasing heating temperature over 90°C the intensity of the peak at 600 nm corresponding to the complex decreased due to the evaporation of I₂ decomposed from I₅⁻, but the peak at 355 nm corresponding to free I₂·I₃⁻ was remained unchanged. From heat treatment at 150°C, the intensity of the peak at 600 nm decreased but the intensity of the complex peak (600 nm) of the sample with 0.5 mol/l boric acid was unaffected. The transmittance and degree of polarization for the films increased and decreased with increasing heat treatment time under heat and a humid atmosphere, respectively. However, this tendency decreased with increasing boric acid concentration and heat treatment. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of boric acid treatment method on the characteristics of poly(vinyl alcohol)/iodine polarizing film

Four types of polyvinyl alcohol (PVA)/iodine complex films were made using different boric acid treatments to prepare polarizing films having high durability under humid and warm atmospheres and to identify the effects of the boric acid treatment method on the formation of the PVA/iodine polarizing film. The four types of films were a PVA iodinated film(I), a PVA film that was iodinated and then treated with boric acid(I‐B), a PVA film that was treated with boric acid and then iodinated(B‐I), and a PVA film that was simultaneously treated with iodine and boric acid(I+B). The concentrations of I₂/KI were 0.03, 0.05, and 0.07 mol/L, and the concentrations of boric acid were 0.1, 0.3, and 0.5 mol/L. Comparing four type films treated with 0.05 mol/L I₂/KI and 0.5 mol/L boric acid, the conformation of PVA/iodine complexes for I‐B film were larger than the others. The degrees of polarization (ρ) of all of the films increased to very high levels (99.9%↑). The durability of I‐B was superior to B‐I or I+B, and the change in the ρ was below 5% because the boric acid treated after iodine treatment reduced the molecular mobility of the PVA/iodine complex chains through intracrosslinking, so that the PVA/iodine complex could not easily collapse. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Polarizer effect and structure of iodinated before and after casting poly(vinyl alcohol) film

Poly(vinyl alcohol) (PVA)/iodine polarizing film was manufactured as follows: PVA iodinated in solution before casting (IBC film) and iodinated again after casting (IBC + IAC film) and then the IBC + IAC film was drawn in boric acid aqueous solution (IBC + IAC polarizing film), to improve the durability of the polarizing film under a humid and warm atmosphere. These effects were examined by investigating the structural and optical properties of the IBC, IBC + IAC, and IBC + IAC polarizing films. In the IBC state, the PVA chain segments that combined boric acid and iodine were regarded as defects of the crystal, the formation of I₃⁻ decreased with respect to weight gain of boric acid. In the IBC + IAC state, the strength of the peak corresponding to I₃⁻ decreased and the I₅⁻ peak increased. The iodine ions penetrated into crystal of the IBC state during the IAC process and formed a new PVA/iodine complex crystal at the 2θ = 20° in the X‐ray diffraction curves. In the IBC + IAC polarizing film state, another type of polarizing film (IBC + IAC polarizing film‐H) containing I₃⁻ ions mainly was manufactured as well as the IBC + IAC polarizing film to compare the effects of the I₃⁻ and I₅⁻ ions on the durability of the polarizing films. The durability of the I₃⁻ ions that were complexed with the PVA chain was higher than the I₅⁻ ions, which could possibly be separated to I₃⁻ and I₂. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of boric acid treatment on the crystallinity and drawability of poly(vinyl alcohol)–iodine complex films

A film iodinated at solution state before casting (BIBC film) and a film iodinated after casting (BIAC film) were prepared by casting an aqueous solution of poly(vinyl alcohol) (PVA) including I₂/KI and boric acid, and by successively soaking the PVA film in aqueous solutions of boric acid and I₂/KI, respectively. The boric acid-induced and I₂/KI-induced weight gains relative to the PVA were 3, 5, 7, and 10%, and 3, 5, 10, and 20%, respectively. The effects of boric acid and iodine on the crystallinity and drawability of the films were investigated. Although the crystalline structure of the BIAC films was not affected by boric acid, the boric acids in the PVA solution containing I₂/KI may have formed intra-molecular cross-links on the PVA chain to accelerate the formation of the PVA–iodine complex evenly, and subsequently interrupt the PVA crystallization through the BIBC film formation to render the resultant film slightly crystalline or practically amorphous. This occurred even at a much lower I₂/KI-induced weight gain (20%) than the minimum weight gain (125%) at which the iodinated at solution state before casting film without boric acid indicated a practically amorphous state. The maximum draw ratio of the films generally decreased with increasing boric acid content, which was mainly attributed to the increase of the extended segments of the PVA chains in the amorphous region due to the cross-links formed with the boric acids. The maximum draw ratios of the BIBC films tended to decrease more severely than those of the BIAC films.     

Structure and processability of iodinated poly(vinyl alcohol) (III)‐structure of films iodinated in solution before casting

Films iodinated at solution before casting (IBC films) were prepared by casting aqueous solutions of 10 wt % poly(vinyl alcohol) (PVA) containing selected quantities of I₂/KI. The quantity of I₂/KI was controlled to obtain 15.2, 39.8, 83.2, 117.0, and 140.1%. The Thermogravimetry (TG) curves of the IBC film exhibited three distinct zones corresponding to the evaporation of H₂O and I₂ molecules (zone I), evaporation of I₂ and partial decomposition of side groups (? OH) (zone II), degradation of the remaining side groups and partial degradation of the main chain (zone III‐1), and degradation of the remaining main chain and the char zone corresponding to KI. The crystalline structure of the film with a weight gain of 15.2% was almost the same as that of the pure PVA, and the film with the weight gain of 140% was almost amorphous. The differential scanning calorimetry (DSC) thermograms of the IBC films with a weight gain of 15.2% and 39.8% indicated endothermic single or double peaks at around 180°C, corresponding to the crystal melting and degradation of side groups; those with weight gains of 83.2% and above indicated exothermic peaks at around 170°C, corresponding to crystallization, and broad endothermic peak at around 180–200°C, corresponding to the crystal melting and degradation of side groups. The dynamic mechanical α_a transition of the IBC film with the weight gain of 140.1% appeared at around 20°C. X‐ray diffraction and DSC analysis of deiodinated films show that the crystal structure, on deiodination of all the IBC films, regardless of crystallinity, returned to that of the pure PVA. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3497–3502, 2006     

Polarization characteristics of poly(vinyl alcohol) films containing metal iodide

The polarization properties of iodine complex layer deposited by oxidation of poly(vinyl alcohol) (PVA) containing metal iodide were investigated. Heat-resistant polarizing films with high polarization efficiency were produced by oxidizing and stretching the PVA containing metal iodide. The results indicate that i) the polarization efficiency of a polarizing film prepared by oxidation of a PVA film containing 1 mmol or more of potassium iodide (KI)/g PVA at 0°C for 120 s in a 10 wt.-% aqueous solution of H₂O₂ and a degree of stretching of 400% is high, ii) the heat resistance of the polarizing film in this experiment is higher than that of a filter prepared from a commercial PVA film.     

Preparation of syndiotacticity‐rich high molecular weight poly(vinyl alcohol)/iodine polarizing film with high water resistance

To enhance durability of poly(vinyl alcohol) (PVA)/iodine polarizing film under humid and warm atmospheres and to identify the effects of syndiotacticity on the polarizing efficiency (PE) and durability of PVA/iodine complex film, we prepared three high molecular weight (PVA)s with similar number‐average degree of polymerization (P_n) of 4000 and with different syndiotactic diad (s‐diad) contents of 53, 56, and 59%, respectively. It was found that syndiotacticity of PVA had a significant influence on the durability of PVA/iodine complex film in warm and humidity conditions (relative humidity of 80% and temperature of 50°C). That is, both desorption of iodine in PVA/iodine film and transmittance of film decreased with increasing syndiotacticity of PVA. In the case of PE, the values of over 99% were obtained at each optimum conditions. The change of PE (durability) of PVA/iodine complex films having P_n of 4000 and s‐diad contents of 56 and 59%, respectively, in warm and humidity conditions was almost zero, whereas those of PVA/iodine film with s‐diad content of 53% and with (P_n)s of 1700 and 4000 were about 60% and 50%, respectively, under same conditions. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Role of adsorbed iodine into poly(vinyl alcohol) films drawn in KI/I2 solution

We have investigated the microstructure of the poly(vinyl alcohol) (PVA) films using small- and wide-angle X-ray scattering (SAXS and WAXS, respectively) techniques. The samples were uniaxially drawn in water or KI/I₂ aqueous solution and then dried in an air-oven at 333 K for 1 h prior to SAXS and WAXS measurements. It was found that for the films drawn in KI/I₂ solution PVA chains in the microfibrillar structure are more extended upon the film drawing compared to the case of the films drawn in pure water, which is resulted from the correlation function analysis on the SAXS data. Adsorbed iodines into the film were anticipated to act as junction points between the microfibrils via the formation of the PVA-iodine complexes.     

Role of boric acid in the formation of poly(vinyl alcohol)-iodine complexes in undrawn films

The role of boric acid in the formation of poly(vinyl alcohol) (PVA)-iodine complexes in undrawn films has been investigated by using wide-angle X-ray diffraction (WAXD) and high-resolution solid-state ¹³C NMR spectroscopy. From UV-vis absorption spectroscopy, it is confirmed that boric acid is necessary for the formation of the complexes in films that are treated with I₂/KI aqueous solutions at relatively low I₂ concentrations. The WAXD profiles indicate that, irrespective of the presence of iodine, crystallite sizes perpendicular to the chain axis become smaller by the addition of boric acid in the swelling media. Moreover, small crystallites and surficial parts of larger crystallites may be partially dissolved in the swelling process with water and boric acid suppresses the re-crystallization in the drying process with or without iodine. The ¹³C spin-lattice relaxation time analysis reveals that there exist two components called the mobile and the less mobile components in the films and the latter component, which contains the complexes and the crystalline component, is increased in the fraction by the presence of boric acid. The evaluation of the CH resonance line shows that some of the intermolecular hydrogen bonds are broken by boric acid, which increases the intramolecular hydrogen bonds. The CH₂ lineshape analysis also reveals that the gauche fraction is appreciably increased in the less mobile component by the addition of boric acid. These facts suggest that boric acid may promote the formation of PVA-iodine complexes particularly in the surficial areas of the crystallites probably by reducing the molecular mobility of the PVA chains by causing cross-linking among them.     

Structure and processability of iodinated poly(vinyl alcohol). II. Drawability of iodinated films

The drawability of poly(vinyl alcohol) (PVA) films iodinated with 0.1, 0.3, 0.5, 1.0, and 2.0 mol/L I₂/KI aqueous solutions was examined with a tensile tester and a hand‐operated drawer at 30–150°C. The structure of the films drawn to a maximum draw ratio (MDR) and deiodinated was determined by X‐ray diffractometry, differential scanning calorimetry, and birefringence. Generally, the improvement of the drawability for the PVA film via iodination was ascertained by the increased breaking strain and decreased yield stress on the stress–strain curves when increasing the I₂/KI concentration of the aqueous solutions used in the iodination. The MDR was generally increased with the concentration of I₂/KI and the draw temperature. However, it diminished instead when close to the highest temperature and concentration of I₂/KI, which was likely due to molecular degradation by the action of iodine as an oxidizer. The variation of the structure of the films drawn and deiodinated seems to be dependent mainly upon the MDR rather than the concentration of I₂/KI. The greater the MDR was, the higher the degree of crystallinity, birefringence, and initial modulus were but the lower the melting temperature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95:1209–1214, 2005     

Role of molecular weight of atactic poly(vinyl alcohol) (PVA) in the polarizing efficiency of PVA/azo dye complex film with high durability

To precisely identify the effect of molecular weight of atactic poly(vinyl alcohol) (a‐PVA) on the durability and polarizing efficiency (PE) of a‐PVA/dye polarizing film, we prepared two (a‐PVA)s with similar syndiotactic diad contents of 54.0%, degrees of saponification of 99.9%, and with different number‐average degrees of polymerization [(P_n)s] of 1700 and 4000, respectively. Through a series of experiments, it was found that molecular weight of a‐PVA had a significant influence on the durability of a‐PVA/dye film in heat and humidity conditions (relative humidity of 80% and temperature of 90°C). That is, both desorption of dye in a‐PVA/dye film and transmittance of film decreased with increasing molecular weight of PVA. The change of PE (durability) of a‐PVA/dye film in heat and humidity conditions was limited to about below 5%. The change of PE of PVA/dye film having P_n of 4000 especially was limited to 1%, whereas that of a‐PVA/iodine film with P_n of 4000, was almost 80% under the same condition. Also, transmittance of the drawn a‐PVA/dye film was far higher than that of the undrawn one. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 967–974, 2005     

Role of boric acid for a poly (vinyl alcohol) film as a cross-linking agent: Melting behaviors of the films with boric acid

We have investigated the role of boric acid as a cross-linking agent for a poly (vinyl alcohol) (PVA) film when the film is immersed in boric acid aqueous solution. DSC results show that the films with boric acid exhibit the higher glass transition temperatures than that of the PVA film without boric acid, when the films are dried after immersing in boric acid aqueous solutions with various boric acid concentrations, implying that boric acid penetrating into the films slows down the PVA molecular motion. Furthermore, simultaneous small-angle X-ray scattering and wide-angle X-ray diffraction measurements were performed on the melting processes of the PVA films with boric acid. We found that the crystallite size increase originated from melting and recrystallization do not occur for the PVA films with boric acid, whereas in the case of the PVA without boric acid the crystallite size is enlarged in both directions parallel and perpendicular to the chain axis via melting and recrystallization on melting. These indicate that chemical reactions of boric acid to the PVA molecular chains in amorphous regions resulted in cross-linking points take place in boric acid aqueous solutions, inhibiting recrystallization on melting, because the cross-links slow down the PVA molecular motion and must not be included in the crystalline domains.     

Starch crosslinked with poly(vinyl alcohol) by boric acid

Starch was crosslinked with poly(vinyl alcohol) (PVA) by boric acid. A suitable plasticizer and defoamer were added to obtain the brei. A film from the starch and PVA (SP film) was prepared by casting. The effects of various factors, such as the crosslinking temperature, the PVA content, and the amounts of glycerol and boric acid, on the tensile strength and breaking elongation were studied. The results showed that the SP film prepared by boric acid crosslinking had excellent mechanical properties. The film‐forming properties, transmittance, and water resistance of the SP film were also investigated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1394–1397, 2005     

Fabrication and characteristics of graphene oxide/nanocellulose fiber/poly(vinyl alcohol) film

Poly(vinyl alcohol) (PVA), PVA/nanocellulose fiber (CNF), and PVA/CNF/graphene oxide (GO) films were prepared simply by casting stable aqueous mixed solutions. FTIR investigation indicated that hydrogen bonding existed between the interface of GO and PVA‐CNF. Scanning electron microscopy and X‐ray diffraction analysis showed that GO was uniformly dispersed in PVA‐CNF matrix. Introducing CNF into PVA caused a significant improvement in tensile strength, and further incorporating GO into PVA/CNF matrix led to a further increase. The tensile strength of the neat PVA film, PVA/CNF composite, and PVA/CNF/GO film (0.6 wt % GO) was 43, 69, and 80 MPa, respectively. Moreover, when incorporating 8 wt % CNF into PVA matrix, O₂ permeability and water absorption decreased from 13.36 to 11.66 cm³/m²/day and from 164.2% to 98.8%, respectively. Further adding 0.6 wt % GO into PVA/CNF matrix resulted in a further decrease of permeability and water absorption to 3.19 cm³/m²/day and 91.2%, respectively. Furthermore, for all composite samples, the transmittance of visible light was higher than 67% at 800 nm. CNF and GO‐reinforced PVA with high mechanical and barrier properties are potential candidates for packaging industry. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45345.     

On the poly(vinyl alcohol)–iodine complexes

The color development due to the complex formation of poly(vinyl alcohol) (PVA) with iodine increased with increasing syndiotacticity of PVA. Isotactic PVA showed no color development. The color development of syndiotacticity-rich PVA film decreased with increasing annealing temperature for films before complexization, whereas that of atactic (commercial) PVA increased with it. Lower temperatures, the elongation of complex film, and the presence of boric acid enhanced the absorbance at 600 nm due to I^?₅. The complexes are assumed to be made by incorporation of polyiodines into aggregates of syndiotactic sequences in PVA. The polarizability and electric conductivity of complex films are investigated. © 1993 John Wiley & Sons, Inc.     

Study on the structure and processibility of the iodinated poly(vinyl alcohol). I. Thermal analyses of iodinated poly(vinyl alcohol) films

To get more information on the structure of iodinated poly(vinyl alcohol) (PVA), thermal analyses of unoriented and oriented PVA films were conducted. Unoriented and oriented PVA films iodinated with aqueous solutions at selected concentrations were carried out by thermogravimetry (TG) and differential scanning calorimetry (DSC). The TG curves for the iodinated film shows four or five weight‐loss zones associated with degradation and evaporation of excess I₂ molecules and I₂ molecules from I, partial OH side groups on PVA, and I₂ from I, the remaining OH groups and the partial main chains, the remaining main chains, and a very small amount of residue from PVA. The char of KI salts remained. By investigating the TG results, it was identified that the amount of I ions increased with increasing I₂/KI up to 65%, but above that weight gain, the rate of increase diminished and the amount of I ions from the I ions increased. The TG curve for the oriented film was very similar to that for the unoriented film except for its greater weight loss at zone I due to narrow space in amorphous region. The DSC thermogram of iodinated films indicated two peaks at 145°C and 160–170°C, corresponding to the melting of crystals and the degradations of OH groups and main chains, respectively. The maximum temperatures of peaks were much lower than that of the untreated one. ©2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2407‐2415, 2004     

Bio‐nanocomposite films based on cellulose nanocrystals filled polyvinyl alcohol/chitosan polymer blend

Bio‐nanocomposite films based on polyvinyl alcohol/chitosan (PVA/CS) polymeric blend and cellulose nanocrystals (CNC) were prepared by casting a homogenous and stable aqueous mixture of the three components. CNC used as nanoreinforcing agents were extracted at the nanometric scale from sugarcane bagasse via sulfuric acid hydrolysis; then they were characterized and successfully dispersed into a PVA/CS (50/50, w/w) blend to produce PVA/CS–CNC bio‐nanocomposite films at different CNC contents (0.5, 2.5, 5 wt %). Viscosity measurement of the film‐forming solutions and structural and morphological characterizations of the solid films showed that the CNC are well dispersed into PVA/CS blend forming strong interfacial interactions that provide an enhanced load transfer between polymer chains and CNC, thus improving their properties. The obtained bio‐nanocomposite films are mechanically strong and exhibit improved thermal properties. The addition of 5 wt % CNC within a PVA/CS blend increased the Young's modulus by 105%, the tensile strength by 77%, and the toughness by 68%. Herein, the utilization of Moroccan sugarcane bagasse as raw material to produce high quality CNC has been explored. Additionally, the ability of the as‐isolated CNC to reinforce polymer blends was studied, resulting in the production of the aforementioned bio‐nanocomposite films with improved properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42004.     

聚乙烯醇/纳米二氧化硅复合偏光膜的制备及结构与性能研究

采用溶液成膜法制备了聚乙烯醇(PVA)/纳米二氧化硅(SiO2)碘系复合偏光膜,并研究了复合偏光膜的结构、偏光性能和热性能。紫外分析表明,随Si场含量的增加,偏光膜的透过率先增加后减小,而偏光率先减小后增加。红外分析表明,纳米SiO2加人后与PVA分子中的-OH发生了相互作用。XRD分析表明,加人纳米SiO2后PVA偏光膜的结晶度下降。TG分析表明,加人纳米SiO2后PVA偏光膜高温热稳定性有所提高。     

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.     

Structure and processability of iodinated poly(vinyl alcohol). IV. Drawability of the films iodinated at solution before casting

The drawability of iodinated at solution before casting (IBC) polyvinyl alcohol films prepared by casting aqueous solutions of 10 wt % PVA containing 15.2, 39.8, 83.2, 117.0, and 140.1% was examined with a tensile tester at 20–60°C. The tensile behavior of IBC films showed that the yield and breaking loads were much lower, and the breaking elongation was even higher than those of the unoriented iodinated after casting (IAC) films as well as the untreated PVA films. The maximum draw ratios of the films with the weight gain of 15.2, 39.8, 83.2, 117, and 140.1% were 4.5, 5.5, 8.5, 8.0, and 7.5, respectively, which were achieved at 20°C in all. The crystallinity of all films increased by the maximum draw, regardless of crystallinity before drawing. The crystalline structure was recovered to the original PVA crystalline lattice by deiodination. Amorphous orientation and initial moduli increased with the maximum draw ratio, while the orientation of crystals was constant. The orientation and moduli increased up to the weight gain of 83.2%, whose highest draw ratio and initial modulus were 8.5 and of 7.1 GPa, respectively, and then decreased. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008