Water vapor absorption and permeability of films based on chitosan and sodium caseinate

The objective of this work was to characterize the moisture sorption and water vapor permeation behavior of edible films made from sodium caseinate and chitosan for future applications as protective layers on foods. Glycerol was used as a plasticizer, and the films were obtained by a casting/solvent‐evaporation method. The moisture sorption kinetics and water vapor permeability (WVP) were investigated. The effect of the addition of glycerol on the WVP characteristics of the films was determined at 25°C with a relative humidity (RH) gradient of 0–64.5% (internal to external). Experimental data were fitted with an exponential function with two fitting parameters. WVP increased with increasing glycerol content in both films, chitosan samples being much more permeable than caseinate ones at any glycerol content. WVPs of sodium caseinate, chitosan, and chitosan/caseinate films with 28 wt % glycerol were also determined for two RH gradients, 0 to 64.5% and 100 to 64.5%, higher WVPs being measured at higher RHs. The moisture sorption kinetics of caseinate films prepared with various glycerol contents were determined by the placement of the films in environments conditioned at 20°C and 75% RH. Peleg's equation and Fick's second law were used to predict the moisture sorption behavior over the entire time period. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Antioxidant and physicochemical properties of blended films based on gelatin‐sodium caseinate activated with natural extracts

Blend films of pigskin gelatin (GEL) and sodium caseinate (SCas) with boldo (B), guarana (G), cinnamon (C), or rosemary (R) extracts added were studied. SCas and extracts addition in blend films significantly increased the gloss and better UV barrier of GEL100 films. Extracts incorporation significantly decreased the rigidity and elongation of GEL100 films, which were significantly improved in GEL75:SCas25 blend films with extracts (EM = 295.69 ± 21.75 MPa and EB = 11.60 ± 3.43%). SCas addition not affected the TS parameter. The water vapor permeability of GEL100 films was reduced in blended films with extracts, showing the lowest value for GEL75:SCas25 + R (0.99 ± 0.07 × 10¹⁰ g s^?1 m^?1 Pa^?1). FTIR and microstructure analyses showed good compatibility for all components. The antioxidant activity of GEL100 was significantly increased with SCas and extracts addition (GEL50:SCas50 + R = 4.31 ± 0.11 mM ), suggesting the application of these films as an active food packaging material. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44467.     

Effect of crosslinking agent on the properties of low-temperature curing PES/PTFE anticorrosive coating

To reduce energy consumption and broaden the scope of application of polyethersulfone/polytetrafluoroethylene (PES/PTFE) coatings, three hybrids have been designed by incorporating PES/PTFE coatings with different contents (0, 10, and 20 wt %) of crosslinking agent consisting of epoxy resin and appropriate curing agent (ER-CA) in the application as low-temperature curing PES/PTFE coatings and named as EP-0, EP-1, and EP-2, respectively. The addition of ER-CA gives rise to satisfactory distribution of PTFE, making PTFE play its roles better and improves barrier properties of the coatings by secondary leveling and its own crosslinking structure, which greatly enhances anticorrosion properties. Compared with EP-0 and EP-2, EP-1 exhibits lower water permeability. Even after long-term exposure to corrosive environments, EP-1 still possesses high anticorrosion properties. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48740.     

谷氨酰胺转移酶处理对大豆分离蛋白、酪蛋白酸钠和明胶可食膜特性的影响

研究了谷氨酰胺转移酶(TGase)对大豆分离蛋白(SPI1和SPI2)、酪蛋白酸钠(NaCN1和NaCN2)及明胶(G1和G2)3类蛋白质成膜特性的影响。研究表明在成膜溶液中加入TGase(8U/g蛋白),可以使SPI、NaCN和明胶等3类蛋白质膜的抗拉强度和表面疏水性有不同程度的改善,其中抗拉强度增加的辐度为13.1%(P≤0.05),而表面疏水性增加的辐度为2%～216%(P≤0.05);明显降低了膜的水分含量、总可溶性物量及透光率。对于断裂伸长率,TGase的处理使G1膜、NaCN2膜、G2膜、NaCN1膜和SPI2膜分别增加16.3%、16.8%、43.0%、72.6%和440.5%,而使SPI1膜降低7.5%。SDS-PAGE电泳分析表明TGase使这3类蛋白质均产生了共价交联。     

The effects of latex coalescence and interfacial crosslinking on the mechanical properties of latex films

The effects of latex coalescence and interfacial crosslinking on the mechanical properties of latex films were extensively investigated by means of several series of model latexes with varying backbone polymer crosslinking density and interfacial crosslinking functional groups. It was found that the tensile strength of crosslinked model latex films increased with increasing gel content (i.e. crosslinking density) of latex backbone polymers up to about 75% and then decreased with further increase in gel, while their elongation at break steadily decreased with increasing gel content. These findings showed that latex particle coalescence was retarded above a gel content of about 75% so that the limited coalescence of latex particles containing gel contents higher than 75% prevented the tensile strength of crosslinked latex films from increasing by further crosslinking the latex backbone polymers. This was contrary to the theory of rubber elasticity that the tensile strength increases with increasing molecular weight and crosslinking density. This limitation was found to be overcome by the interfacial crosslinking among latex particles during film formation and curing. This paper will discuss the effects of both latex backbone polymer and interfacial crosslinking on latex film properties. It will also discuss the development of self-curable latex blends and structured latexes containing co-reactive groups: oxazoline and carboxylic groups.     

Film formation and surface properties of enzymatically crosslinked casein films

The use of renewable materials as barrier material is currently intensively investigated. Biopolymers such as polysaccharides, lipids, and proteins have been studied as barrier materials. Protein‐based films often possess good gas barrier properties, but because of their hydrophilic nature the gas barrier properties are sensitive to humidity. The improvement of the properties of sodium caseinate barrier films in potential packaging applications was studied by investigating the effects of enzymatic treatment and plasticizer on the film properties. Oxidoreductases Trametes hirsuta laccase (ThL) and Trichoderma reesei tyrosinase (TrTyr) were compared with transglutaminase for crosslinking of the sodium caseinate molecules in the films and coatings. All of the studied enzymes were able to crosslink sodium caseinate. Film solubility tests, protein electrophoresis, contact angle measurements, and atomic force microscopy studies showed that TrTyr treatment results in sodium caseinate films and coatings with better overall properties compared to treatment with ThL. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of Ca2+ induced crosslinking on the mechanical and barrier properties of cast alginate films

The use of alginate as a coating material for packaging applications is currently limited due to its difficult processability and high moisture sensitivity. Therefore, this study addresses the crosslinking and scale‐up to a continuous application. Three different crosslinking agents were applied: CaCl₂ with ethylene diamine tetraacetic acid and two low soluble salts (CaHPO₄ and CaCO₃). Those were incorporated by internal setting in an alginate matrix with varying Ca²⁺ concentration ( ) and ratio. With the addition of Ca²⁺, the tensile strength and elongation at break of the cast alginate films increased. This was optimal for a of 0.010–0.015 g (g alginate)^?1 dependent on the crosslinking agent. The decrease in water vapor and oxygen permeability due to crosslinking was independent of the crosslinking agent. However, the optimal aiming to decrease permeability was different for the crosslinking agents: CaHPO₄ showed best results at a of 0.010 g (g alginate)^?1, CaCl₂ at 0.012 g (g alginate)^?1, and CaCO₃ at 0.027 g (g alginate)^?1. Upon all analyzed properties CaHPO₄ was the most promising crosslinking agent for alginate. Moreover, selected alginate formulations were successfully processed in a continuous lacquering plant. The produced two‐layer systems have very low oxygen permeabilities which can be further reduced by crosslinking. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45754.     

Preparation of acrylic copolymers and crosslinking agents and properties as a film

Copolymers of butyl acrylate (BA)‐methyl methacrylate (MMA)‐acrylic acid (AA) and intraparticle crosslinking agents containing N‐methylol acrylamide (NMA) and ethylene glycol dimethacrylate (EGDMA) were prepared by emulsion copolymerization. After that, films were prepared from the mixture of copolymers and the interparticle crosslinking agents. The interparticle crosslinking agents were prepared from hexamethylene diisocyanate and aziridine ethanol. Mixtures of the copolymer and the interparticle crosslinking agent were cast to films and crosslinked in a convection oven. The effects of the contents of the intra/interparticle crosslinking agents were also evaluated. By increasing the contents of EGDMA, roughness of the films was increased because of the effects of EGDMA acting as an intraparticle crosslinking agent. By increasing the contents of the interparticle crosslinking agent, roughness was also increased by the reaction between the copolymers and interparticle crosslinking agent. Tensile strength and water and chemical resistance of the film were increased, whereas elongation of film was decreased by increasing the contents of interparticle crosslinking agents. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of crosslinking on the mechanical properties and biodegradability of soybean protein‐based composites

A green composite with good mechanical properties and acceptable biodegradability was developed using wood flour and soybean protein that was modified by thermal‐caustic degradation and chemical crosslinking with glyoxal and polyisocyanate (PMDI). Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM) in combination with the traditional evaluations were employed to investigate the structure, morphology, and properties of the crosslinked soybean protein and the crosslinking‐modified wood/soybean protein composites to understand the effects of the crosslinker species on the mechanical properties, water resistance, and microbial biodegradation of soybean protein‐wood flour composites. The results indicated that the chemical crosslinking modification could improve the mechanical properties and water resistance but decrease the biodegradability of the wood/protein composite to a certain extent. Both glyoxal and PMDI alone as crosslinkers could not perfectly modify the soybean protein because of the high reactivity of PMDI and low crosslinking reactivity of glyoxal. The incorporation of glyoxal with PMDI could result in the desired crosslinking efficiency and good interfacial adhesion by compromising the advantages and disadvantages of glyoxal or PMDI alone as crosslinkers, which balanced the performances of the wood flour/soybean protein composite. The preferable combination crosslinker was composed of 50 wt % glyoxal and 50 wt % PMDI. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41387.     

Characterization of chitosan/caseinate films

Films made from sodium caseinate and/or chitosan, using glycerol as plasticizer, were prepared by casting from aqueous solutions. Films cryo‐fractured surfaces were examined by SEM. FTIR spectra of the chitosan/caseinate films showed an increase in the intensity of the amide band, corresponding to the strong interactions developed by the polyelectrolytic complexation of both components. Addition of 28 wt% of glycerol to caseinate films, conditioned at 50% relative humidity (RH), reduced the modulus from 2908 to 250.9 MPa, while the ultimate elongation increased from 4 to 63.2%. Increment to 80% RH further reduced the modulus down to 52.8 MPa. Similar results were found for the glycerol plasticization of chitosan films. The complex films showed a moderate improvement of the tensile strength (19.6 MPa) and an increase of the impact strength (35.6 GPa) with respect to those corresponding of chitosan films (17 MPa and 26.6 GPa, respectively). These properties were markedly improved with respect to those of caseinate (6.2 MPa and 13.4 GPa, respectively). The interactions developed between the cationic polymer chitosan, and the Na‐caseinate carboxyl groups, lead to polyelectrolyte complexation in forming the film, which is proposed as the reason for improvement with respect to caseinate or chitosan films. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Improving wet strength of soy protein films using oxidized sucrose

The chemical modification of soy protein isolate (SPI) with various amounts of oxidized sucrose was performed in this study. The poor mechanical properties and lack of hydrolysis resistance of SPI have limited its applications in various fields. Although chemical modification proved to be an effective method to enhance the properties of SPI films, current SPI modifiers are either expensive, toxic, or do not impart the satisfiable properties to the modified materials. In this research, the possibility of modification of SPI films using oxidized sucrose to improve their strength and stability was examined. At optimal conditions, oxidized sucrose‐modified SPI films showed about 50% higher wet strength than the control films. The melting temperature of modified SPI film was 26°C higher than the unmodified control. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41473.     

Preparation of resistant starch/poly(vinyl alcohol) blend films with added plasticizer and crosslinking agents

We report on the physical properties of films synthesized with native corn starch (NCS) and resistant starch (RS4) prepared with NCS. NCS and RS4/poly(vinyl alcohol) (PVA) blend films were synthesized with a mixing process and casting method. Glycerol (GL) and citric acid (CA) were used as additives. Glutaraldehyde (GLU) was used as a crosslinking agent of the films. RS4 was synthesized with sodium trimetaphosphate and sodium tripolyphosphate as a crosslinker. Then, the RS4 thus synthesized was confirmed by the pancreatin–gravimetry method, swelling power, differential scanning calorimetry, and X‐ray diffraction. The tensile strength, elongation, swelling behavior, and solubility of the films were measured. The results of the measurements indicated that the RS4‐added film was better than the NCS‐added film. In particular, the RS4/PVA blend film with CA as an additive showed physical properties superior to those of the other films. Also, the physical properties with GLU added as a crosslinking agent to the films were investigated. With increasing GLU contents, the tensile strength increased but the elongation, swelling behavior, and solubility values of the GL‐added and CA‐added films decreased. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Water absorbance and thermal properties of sulfated wheat gluten films

Wheat gluten films of various thicknesses formed at 30–70°C were treated with cold sulfuric acid to produce sulfated gluten films. Chemical, thermal, thermal stability, and water uptake properties were characterized for neat and sulfated films. The sulfated gluten films were able to absorb up to 30 times their weight in deionized water. However, this value dropped to 3.5 when the film was soaked in a 0.9% (w/w) NaCl solution. The films were also soaked 4 times in deionized water, and each soaking resulted in a reduced water uptake capacity. The temperature of film formation had no effect on the final water uptake properties. Also, thinner films had higher concentrations of sulfate groups than thicker films; this resulted in higher water uptake values. In addition, sulfated gluten films had comparable glass‐transition temperatures but lower thermal stabilities than the neat gluten films. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Influence of crosslinkers and crosslinking method on the properties of gelatin films extracted from leather solid waste

Gelatin was extracted from chrome tanned leather waste with the aim to produce a durable coating or film. Crosslinking has shown to improve the physical performance of a film/coating. The effect of the method of crosslinking and the use of different crosslinking agents were studied. The extracted gelatin was crosslinked either by immersion of preformed films into a crosslinker solution (Method A) or by the addition of the crosslinking reagent to the gelatin solution prior to film formation (Method B). The different results obtained between both methods may be due to: the relative concentration of crosslinking reagent, the introduction of crosslinks within different regions of gelatin (triple helical regions and random coil regions), and the reaction rate. Method A of crosslinking is more likely to form crosslinks outside but close to the triple helical regions, disrupting the order and stability of the helical structure. Crosslinks may form preferentially within the random coil regions when Method B of crosslinking is used. Both methods led to the formation of chemical crosslinks in the extracted gelatin films, as demonstrated by the reduction of the degree of aqueous swelling and the proportion of low molecular weight fractions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Improved zein films using polyethylenemaleic anhydride

The effect on the physical properties and solubility of corn protein (zein) films was studied after reaction of zein with polyethylenemaleic anhydride (PEMA). Reactions were carried out in dimethylformamide (DMF) solution where the concentration of PEMA was varied between 0 and 6%. After reaction at room temperature, cast films were prepared, and the physical and solubility properties were determined. Incorporating more than 2% PEMA provided films with increased tensile strength and elongation. Incorporating 6% PEMA provided films with higher tensile strength (32–42 MPa) and improved solvent resistance (100–21% solubility) relative to control. If the films were heated in an oven, the film's solubility decreased further. Solution rheology experiments demonstrated that the zein and PEMA formed a cross‐linked gel with time in DMF. Dynamic mechanical analysis experiments have shown that the PEMA‐modified zein films undergo a dramatic loss in modulus on reaching 116°C, whereas the control experiences this loss at 98°C. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40122.     

交联剂对聚醚酰胺弹性纤维力学性能的影响

采用两步法工艺路线,以PA6齐聚物、聚醚和少量交联剂为原料共聚合成聚醚酰胺热塑性弹性体(TPAE)。对TPAE进行模拟纺丝,对初生纤维进行拉伸和热定型。测定了纤维的力学性能。利用WAXD分析了交联剂对TPAE结晶性能的影响,讨论了纤维弹性及回复率与纺丝条件、交联剂用量的关系。结果表明,随交联剂含量的增加,拉伸丝较初生丝的结晶度提高幅度小,交联剂的化学交联作用明显。交联剂的引入使TPAE纤维断裂强度和弹性回复率提高,断裂伸长率降低,交联剂质量分数(相对PA6)为0.7%时,TPAE纤维的弹性回复率可提高到95%以上。     

交联结构对苯类吸收树脂性能的影响

采用悬浮聚合法制备了球形苯类吸收树脂,研究了交联剂用量与树脂的吸收倍率、交联密度和凝胶分数之间的关系,探讨了交联结构对树脂吸收和释放动力学的影响,并采用扫描电镜考察了树脂的微观形貌。结果表明:随着交联剂用量的增加,吸收树脂的凝胶分数和交联密度不断增大,吸收倍率出现峰值;随着交联密度的提高,吸收树脂对甲苯的吸收速率和释放速率均减慢,吸收动力学常数与释放扩散系数都不断降低;树脂对甲苯的吸收动力学过程符合准一级动力学方程;得出了形式简洁的吸收树脂释放动力学方程,能够很好地描述吸收树脂释放甲苯的动力学行为;吸收树脂的交联结构稳定,再生重复使用10次以后树脂微球的大小、形貌和吸收倍率均无明显变化。     

Effect of crosslinking on the physicochemical properties of proton conducting PVDF-g-PSSA membranes

Poly(vinylidene fluoride) (PVDF) membranes, radiation-grafted with styrene and sulfonated, were studied as a candidate material for polymer electrolyte fuel cell (PEFC). In particular the effect of the use of crosslinkers in the polymer structure was investigated using bis(vinyl phenyl)ethane (BVPE) and divinylbenzene (DVB) as reagents. Water uptake in the H+ form, proton conductivity and ion exchange capacity of the PVDF-g-PSSA membranes, as well as transport properties of oxygen and hydrogen were determined at room temperature. Crosslinking with DVB resulted in a more pronounced decrease in the properties; the use of BVPE had no significant influence. Even on the permeation of oxygen and hydrogen the BVPE had little effect: the diffusion coefficient and solubility remained at the same level as for the non-crosslinked membranes. Increasing the membrane thickness was found to be at least as effective in reducing the oxygen permeation rate as using crosslinkers.     

The synthesis and characteristics of sodium alginate/graphene oxide composite films crosslinked with multivalent cations

Association of a method of the incorporation of graphene oxide (GO) into sodium alginate (Na‐alg) polymer matrix with a method of the use multivalent cations crosslinker was put forward to synthesize novel Na‐alg/GO nanocomposite films. The structures, morphologies, and the properties of Na‐alg/GO films were characterized by Fourier transform infrared (FTIR) spectroscopy, X‐ray diffraction (XRD), field‐emission scanning electron microscopy (FE‐SEM), thermogravimetric analysis (TGA), and tensile tests. The results revealed that the interlayer distance of GO sheets increased from 0.83 nm to 1.08 nm after assembling with Na‐alg, and Na‐alg inserted into GO layers crosslinking with multivalent cations increased the interlayer distance further. Ionic crosslinking significantly enhanced thermal and mechanical properties of Na‐alg/GO nanocomposite films. In particular, Fe³⁺ led to Na‐alg/GO nanocomposite films of significantly higher tensile strength and modulus than Ca²⁺ and Ba²⁺. The excellent thermal and mechanical properties of these novel Na‐alg/GO nanocomposite films may open up applications for Na‐alg films. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43616.     

Insoluble porous conjugated polymer films via phase separation and photo‐crosslinking for the trace detection of 2,4‐dinitrotoluene

A novel conjugated polymer film with microscale/submicroscale porous morphology fabricated from crosslinked poly(fluorene‐co‐carbazole) (PFC1) was developed for the detection of 2,4‐dinitrotoluene (DNT). The fluorescent conjugated polymer PFC1 with pendant photo‐crosslinkable coumarin groups was synthesized by Suzuki coupling polymerization. Taking advantage of the phase separation of PFC1/polystyrene (PS) blends in the film and the solvent‐resistant network, porous structured films were prepared by removal of PS. Films with porous morphologies exhibited marked responsive sensitivity to trace DNT vapor due to the unique porous structure favoring the diffusion of and association with DNT molecules. The formation of a crosslinked network by dimerization of the coumarin moieties may be beneficial for isolating the polymeric backbones, thus to some extent preventing chain aggregation. This facile fabrication method enabled the crosslinked porous films to be efficient fluorescence chemosensors towards the detection of trace amounts of DNT vapor.© 2012 Society of Chemical Industry