Enhancing mechanical properties of poly(vinyl alcohol) blown films by drawing and surface crosslinking

Thermal blowing of poly(vinyl alcohol) (PVA) film was successfully realized based on molecular complexation. Ways to enhance the performance of the PVA blown films (drawing and surface crosslinking) were studied. The experimental results showed that water exists in PVA films in different states through hydrogen bonds with PVA and other modifiers and influences the drawability of PVA films, as well as the structure and properties of the stretched films. When the initial water content of the film was higher than 35.0%, the draw ratio of the PVA film was quite large because of the effects of the bound water with PVA, as well as the plasticization of free water. With the increase of the initial water content in PVA, the free water content and draw ratio of the films increased but the strength of the films decreased because of the higher residual water in the films. Surface crosslinking can improve the stretchability of PVA films because more water remains in the films and disrupts the hydrogen bonding of PVA. In addition, crosslinking enhances the mechanical properties of stretched PVA films. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 774–779, 2005     

聚乙烯醇/淀粉薄膜的力学性能及结晶行为

通过熔融共混挤出的方法,制备了聚乙烯醇(PVA)/淀粉薄膜,研究了淀粉加入量对PVA/淀粉薄膜力学性能的影响。采用差示扫描量热法研究了PVA薄膜和PVA/淀粉薄膜的结晶行为及非等温结晶动力学。结果表明:随着淀粉含量的增加.PVM淀粉薄膜的拉伸强度和断裂伸长率下降。在淀粉质量分数为25%时,薄膜的拉伸强度为17.05 MPa.断裂伸长率为425.00%.仍能达到包装薄膜对力学性能的要求。PVA/淀粉薄膜熔融温度和结晶温度均随着淀粉加入量的增加向低温方向移动;在相同的冷却速率下,共混薄膜的结晶速率低于PVA薄膜,同时结晶度也下降.导致力学性能下降。     

Effect of poly(ethylene methyl acrylate) copolymer on thermal,morphological, and mechanical properties of polypropylene copolymer blown films

Blends of polypropylene copolymer (PP‐cp) and poly(ethylene methyl acrylate) [poly(EMA)] copolymer blends were processed by blown film extrusion. The orientation and crystallinity of PP‐cp matrix in the blend did not change significantly with the addition of EMA. The low machine direction and transverse direction tear strengths, which are observed for neat polypropylene blown films more than doubled at 6 wt % or higher content of EMA. The increase in tear properties was mainly attributed to a fine dispersion of EMA in the matrix with an average particle size of 100–500 nm and the formation of elongated domains. The dispersed nonrounded EMA domains, resulting from the blown‐film process, enhance better energy dissipation mechanism with the formation of an extended plastic zone in the blend films as compared with that in pure PP‐cp films. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Sustainable and biodegradable poly(butylene succinate-co-terephthalate)/poly(propylene carbonate) blown films with enhanced compatibility,mechanical, and barrier properties

In this study, a novel environment-friendly PBST/PPC-based blown film was prepared using maleic anhydride (MA) as a reactive compatibilizer to enhance the compatibility between poly(butylene succinate-co-terephthalate) (PBST) and poly(propylene carbonate) (PPC). Results of rheological testing and gel permeation chromatography (GPC) indicated that MA reacted with PBST/PPC during melt-blending extrusion. Morphological analysis of the cryo-fractured surfaces of PBST/PPC blend showed significantly improved compatibility between PBST and PPC with the addition of MA. Moreover, the Young's modulus, tensile strength, breaking strain, and tear strength of PBST/PPC/MA blown films increased with an increase in MA content. In comparison to PBST/MA blown film without PPC, the barrier property of PBST/PPC/MA blown films was improved. In addition, in vitro cell experiments showed that the PBST/PPC/MA blown film was suitable for the growth of mouse fibroblast (L929) cells. In vitro ecotoxicity testing on mung bean plant showed that the extracts from the PBST/PPC/MA blown film had no negative effects on the development of mung bean plant. Furthermore, degradability testing in soil also proved that the PBST/PPC/MA blown film had good biodegradability. Thus, the PBST/PPC/MA blown film can be used in fields, such as food packaging and agricultural mulch film.     

Study of the miscibility and crystallization behavior of poly(ethylene oxide)/poly(vinyl alcohol) blends

The miscibility and crystallization behavior of poly(ethylene oxide)/poly(vinyl alcohol) (PEO/PVA) blends were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and polarizing optical microscopy. Because the glass‐transition temperature of PVA was near the melting point of PEO crystalline, an uncommon DSC procedure was used to determine the glass‐transition temperature of the PVA‐rich phase. From the DSC and DMA results, two glass‐transition temperatures, which corresponded to the PEO‐rich phase and the PVA‐rich phase, were observed. It was an important criterion to indicate that a blend was immiscible. It was also found that the preparation method of samples influenced the morphology and crystallization behaviors of PEO/PVA blends. The domain size of the disperse phase (PVA‐rich) for the solution‐cast blends was much larger than that for the coprecipitated blends. The crystallinity, spherulitic morphology, and isothermal crystallization behavior of PEO in the solution‐cast blends were similar to those of the neat PEO. On the contrary, these properties in the coprecipitated blends were different from those of the neat PEO. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1562–1568, 2004     

Crosslinked poly(vinyl alcohol) and starch composite films. II. Physicomechanical,thermal properties and swelling studies

Poly(vinyl alcohol) (PVA) was blended with 10, 20, 30, 40, and 50 wt % of starch with and without crosslinking by solution casting process. The solution‐casted films were dried and tested for physicomechanical properties like tensile strength, tensile elongation, tensile modulus, tear and burst strengths, density, and thermal analysis by differential scanning calorimetry (DSC). These PVA/starch films were further characterized for moisture content; solubility resistance in water, 5% acetic acid, 50% ethanol, and sunflower oil; and swelling characteristics in 50% ethanol and sunflower oil. The crosslinked PVA/starch composite films show significant improvement in tensile strength, tensile modulus, tear and burst strengths, and solubility resistance over the uncrosslinked films. Between the crosslinked and uncrosslinked films, the uncrosslinked films have higher tensile elongation, moisture content, moisture absorption, and swelling over the crosslinked films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 909–916, 2007     

Structure and properties of blends of poly(ethylene-co-vinyl alcohol) with poly(styrene-co-maleic anhydride)

In the present study, ethylene/vinyl alcohol (EVAL) copolymers with different hydroxyl contents were melt mixed with styrene/maleic anhydride (SMA) copolymers. These two copolymers have functional groups capable of reacting intermolecularly, giving stable products. All EVAL copolymers were prepared from the same ethylene/vinyl acetate (EVA) copolymer by controlled hydrolysis. The blends, prepared at constant temperature and rotation speed in the rheomixer, were characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermo-gravimetric analysis, as well as mechanical properties and extraction experiments. All the above measurements lead to the conclusion that a certain part of hydroxyls of EVAL have reacted with anhydride groups of SMA, leading to the formation of branched and cross-linked products. The effect of (1) the molar ratio of hydroxyl/maleic anhydride functional groups, (2) the overall concentration of the functional groups, and (3) the mixing time on the structure and properties of the blends are discussed. Emphasis is given on the influence of these factors on the tensile strength, the elongation at break, and impact strength of the products. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 983–999, 1997     

Surface grafting of a poly(organophosphazene) onto poly(vinyl alcohol) and poly(ethylene-co-vinyl alcohol) using triethoxysilane as a coupling agent

Triethoxysilane HSi(OEt)₃ was used as coupling agent to graft a poly(organophosphazene) (POPZ) containing allylic functions to the surface of poly(vinyl alcohol) or poly(ethylene-co-vinyl alcohol) films. Hydrolyzed HSi(OEt)₃, which contained both inorganic (Si–OH) and organic (Si–H) reactivities, acted at the interface between the hydroxylated substrates (via a condensation reaction) and the allylic functions in POPZ (via a hydrosilylation reaction). Starting materials and grafting surfaces were studied by ATR-IR and XPS spectroscopies and contact angle measurements. Data obtained indicated that different POPZ layers were produced, depending on whether the functionalization of materials with silane, and the grafting reaction were separately or simultaneously made. The POPZ layer thickness was higher when the grafting reaction was preceded by the POPZ functionalization. In each cases, the modified surfaces showed marked increases in hydrophobicity character. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1965–1974, 1998     

High molecular weight poly( -lactide) and poly(ethylene oxide) blends: thermal characterization and physical properties

The miscibility of high molecular weight poly( -lactide) PLLA with high molecular weight poly(ethylene oxide) PEO was studied by differential scanning calorimetry. All blends containing up to 50 weight% PEO showed single glass transition temperatures. The PLLA and PEO melting temperatures were found to decrease on blending, the equilibrium melting points of PLLA in these blends decreased with increasing PEO fractions. These results suggest the miscibility of PLLA and PEO in the amorphous phase. Mechanical properties of blends with up to 20 weight% PEO were also studied. Changes in mechanical properties were small in blends with less than 10 weight% PEO. At higher PEO concentrations the materials became very flexible, an elongation at break of more than 500% was observed for a blend with 20 weight% PEO. Hydrolytic degradation up to 30 days of the blends showed only a small variation in tensile strength at PEO concentrations less than 15 weight%. As a result of the increased hydrophilicity, however, the blends swelled. Mass loss upon degradation was attributed to partial dissolution of the PEO fraction and to an increased rate of degradation of the PLLA fraction. Significant differences in degradation behaviour between PLLA/PEO blends and (PLLA/PEO/PLLA) triblock-copolymers were observed.     

The morphology,rheological, and mechanical properties of wood flour/starch/poly(lactic acid) blends

An entirely biosourced blend composed of poly(lactic acid) (PLA), starch, and wood flour (WF) was prepared by a co‐extruder with glycerol as a plasticizer. The morphology, rheological properties, and mechanical properties of the WF/starch/PLA blends were comprehensively analyzed. The results showed that with the decrease of the starch/WF ratio, the morphology experienced a large transformation, and the compatibility of the blends was found to be superior to other blends, with a starch/wood flour ratio of 7/3. The dynamic mechanical thermal analysis (DMA) results demonstrated the incompatibility of the components in WF/starch/PLA blends. Following the decrease of the starch/WF ratio, the storage modulus (G″) and the complex viscosity (η*) of the blends increased. The mechanical strength first increased, and then decreased with the increase of the WF concentration. The water absorption results showed that the water resistance of the blends was reduced with the lower starch/WF ratio. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44743.     

Morphology and mechanical properties of pullulan/poly(vinyl alcohol) blends crosslinked with glyoxal

We prepared pullulan/poly(vinyl alcohol) (PVA) blend films by casting the polymer solution in dimethyl sulfoxide. Their morphology and mechanical properties were investigated. Scanning electron micrographs revealed that the pullulan was immiscible with PVA over the entire composition range. The tensile strength and modulus of the blend films were lower than those predicted by the upper bound composite equation. To improve the mechanical properties, we investigated the reaction of the 40/60 blend with glyoxal. The infrared spectral change and the increase in the glass‐transition temperature (corresponding to the PVA component) accompanying the reaction indicated that crosslinking with glyoxal had proceeded. The crosslinked films were homogeneous and had higher tensile strengths and moduli than the simple blend. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2273–2280, 2001     

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     

Studies on aluminum-isopropoxide doped poly(ethylene oxide), poly(vinyl alcohol), and poly(ethylene oxide)-poly(vinyl alcohol) blends

Poly(ethylene oxide), poly(vinyl alcohol), and their blend in a 40 : 60 mole ratio were doped with aluminum isopropoxide. Their structural, thermal, and electrical properties were studied. Aluminum isopropoxide acts as a Lewis acid and thus significantly influences the electrical properties of the polymers and the blend. It also acts as a scavanger for the trace quantities of water present in them, thereby reducing the magnitude of proton transport. It also affects the structure of polymers that manifests in the thermal transformation and decomposition characteristics. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2147–2157, 1998     

Melt characteristics,mechanical, and thermal properties of blown film from modified blends of poly(butylene adipate‐co‐terephthalate) and poly(lactide)

Blown films from poly(butylene adipate‐co‐terephthalate) and poly(lactide) (PLA) blends were investigated. The blends were prepared in a twin‐screw extruder, in the presence of small amounts of dicumyl peroxide (DCP). The influence of DCP concentration on film blowing, rheological, mechanical, and thermal properties of the blends is reported in this article. Rheological results showed a marked increase in polymer melt strength and elasticity with the addition of DCP. As a consequence, the film homogeneity and the stability of the bubble were improved. The modified blend films, compared with the unmodified blend, showed an improvement in tensile strength and modulus with a slight loss in elongation. Fourier transform infrared and gel results revealed that chain scission and branching were more significant than crosslinking when the DCP loadings in the blends were not higher than 0.7%. A reduction in melt temperatures of PLA was observed due to difficulty in chain crystallization. The concentrations of DCP strongly affected the melting temperatures but had an insignificant effect on the decomposition behavior of the blends. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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     

Blends of poly(ethylene terephthalate) and poly(butylene terephthalate)

Commercial grade poly(ethylene terephthalate), (PET, intrinsic viscosity = 0.80 dL/g) and poly(butylene terephthalate), (PBT, intrinsic viscosity = 1.00 dL/g) were melt blended over the entire composition range using a counterrotating twin‐screw extruder. The mechanical, thermal, electrical, and rheological properties of the blends were studied. All of the blends showed higher impact properties than that of PET or PBT. The 50:50 blend composition exhibited the highest impact value. Other mechanical properties also showed similar trends for blends of this composition. The addition of PBT increased the processability of PET. Differential scanning calorimetry data showed the presence of both phases. For all blends, only a single glass‐transition temperature was observed. The melting characteristics of one phase were influenced by the presence of the other. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 75–82, 2005     

Preparation and properties of biodegradable thermoplastic starch/poly(hydroxy butyrate) blends

The vital differences using three types of thermoplastic starches (TPS), including potato starch, corn starch, and soluble potato starch, with two different gelatinization degrees to blend with poly(hydroxy butyrate) (PHB) are thoroughly discussed in this study. For blends containing a certain amount of PHB, thermal stability remains in a certain degree. In all cases of this study, mechanical properties of TPS blended with PHB confer higher performance than those of pristine TPS. In particular, a significant increase on tensile strength and tear strength is observed for TPS (potato starch) blended with PHB at low gelatinization degree. A suitable degree of gelatinization of starch is critical to achieve optimum performance. The investigation on the morphological observation partly features the supporting evidence of the above findings. The assessment of biodegradability indicates that the values of water absorption and weight loss increase with increasing treatment period and glycerol content, but decrease with increasing amount of PHB content. Among three types of starches investigated, the TPS (soluble starch)/PHB blend gives the highest level of water absorption and weight loss. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2371–2379, 2006     

Crosslinking reaction of poly(vinyl alcohol) with poly(acrylic acid) (PAA) by heat treatment: Effect of neutralization of PAA

The crosslinking reaction of poly(vinyl alcohol) (PVA) by esterification using poly(acrylic acid) (PAA) as a crosslinking reagent was investigated to obtain highly insoluble PVA materials. Blend films of PVA and PAA (PVA/PAA = 8/2) were prepared to examine the effect of degree of neutralization (DN) in PAA and heat‐treatment conditions on the degree of crosslinking reaction. The degree of crosslinking reaction varied significantly when the DN of PAA changed. The optimum DN for the crosslinking reaction was in the range of 5 to 10 mol %. In the case of unneutralized PAA, the degree of crosslinking reaction was at most 15 mol % by heat treatment for 20 min at 200°C. Applying partially neutralized PAA (DN = 10 mol %) raised the degree to about 40 mol % under the same heat‐treatment conditions. FTIR analysis revealed that the hydroxyl group of PVA in the film blended with unneutralized PAA was degraded to a greater degree than that with partially neutralized PAA as a result of heat treatment. It was found that heat treatment at a low pH condition enhances the degradation of the hydroxyl group of PVA, resulting in a decrease of the number of crosslinking sites by esterification. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2420–2427, 2003     

聚乙烯醇/凹凸棒黏土纳米复合膜的制备及其性能

以聚乙烯醇(PVA)和提纯凹凸棒黏土(APT)为原料,采用溶液流延成膜法,制备了系列不同APT含量的PVA/APT纳米复合膜。采用XRD、FTIR和SEM对复合膜的结构进行了表征,测试了复合膜的热性能、力学性能和耐水性能。结果表明,APT可均匀分散在PVA基体中,APT的加入使得PVA的结晶度有所下降但并未改变其晶型。APT与PVA通过氢键作用,改善了复合膜的热稳定性、力学性能和耐水性。当APT含量为4%时,纳米复合膜有最优的性能。     

Biodegradable polymer blends of poly(lactic acid) and poly(ethylene glycol)

Poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG) were melt-blended and extruded into films in the PLA/PEG ratios of 100/0, 90/10, 70/30, 50/50, and 30/70. It was concluded from the differential scanning calorimetry and dynamic mechanical analysis results that PLA/PEG blends range from miscible to partially miscible, depending on the concentration. Below 50% PEG content the PEG plasticized the PLA, yielding higher elongations and lower modulus values. Above 50% PEG content the blend morphology was driven by the increasing crystallinity of PEG, resulting in an increase in modulus and a corresponding decrease in elongation at break. The tensile strength was found to decrease in a linear fashion with increasing PEG content. Results obtained from enzymatic degradation show that the weight loss for all of the blends was significantly greater than that for the pure PLA. When the PEG content was 30% or lower, weight loss was found to be primarily due to enzymatic degradation of the PLA. Above 30% PEG content, the weight loss was found to be mainly due to the dissolution of PEG. During hydrolytic degradation, for PLA/PEG blends up to 30% PEG, weight loss occurs as a combination of degradation of PLA and dissolution of PEG. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1495–1505, 1997