Dynamic–Mechanical Properties of Bioartificial Polymeric Materials

Bioartificial polymeric materials represent a new class of polymeric materials based on blends of synthetic and natural polymers, designed with the purpose of producing new materials with enhanced properties with respect to the single components. The mechanical properties of bioartificial materials prepared using poly(vinyl alcohol) (PVA), poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMAA) as synthetic components, and collagen (SC), gelatin, starch, hyaluronic acid (HA) and dextran as biological components, were investigated by dynamic mechanical thermal analysis. The materials were prepared in the form of films or hydrogels and treated by glutaraldehyde (GTA) vapour or thermal dehydration in order to reduce their solubility in water. The results indicate that SC/PVA, gelatin/PVA and starch/PVA films behave as biphasic systems, showing good mechanical properties over a wide range of temperature. It was observed that the GTA procedure affects only the biological component of the SC/PVA and gelatin/PVA blends, whilst the thermal treatment influences mainly the synthetic polymer. In the case of HA/PVA hydrogels, a modulus variation was found with the HA content related to the organization degree and perfection of the PVA network structure. It seems evident that, in the experimental conditions used, dextran/PAA mixtures behave as miscible blends showing a glass transition intermediate between those of the pure components. With both untreated and GTA-treated gelatin/PMAA blends, it was not possible to evaluate the miscibility of the systems; it could only be affirmed that these materials show good mechanical properties over a wide range of temperature. © 1997 SCI.     

Enhanced oxygen‐barrier and water‐resistance properties of poly(vinyl alcohol) blended with poly(acrylic acid) for packaging applications

To enhance the oxygen‐barrier and water‐resistance properties of poly(vinyl alcohol) (PVA) and expand its food packaging applicability, five crosslinked poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) blend films were prepared via esterification reactions between hydroxyl groups in PVA and carboxylic acid groups in PAA. The physical characteristics of the blends, including the thermal, barrier, mechanical and optical properties, were investigated as a function of PAA ratio. With increasing PAA content, the crosslinking density was significantly increased, resulting in changes in the chemical structure, morphology and crystallinity of the films. The oxygen transmission rate of pure PVA decreased from 5.91 to 1.59 cc m^?1 day^?1 with increasing PAA ratio. The water resistance, too, increased remarkably. All the blend films showed good optical transparency. The physical properties of the blend films were strongly correlated with the chemical structure and morphology changes, which varied with the PAA content. © 2016 Society of Chemical Industry     

老化对NR硫化胶的影响

研究了热空气老化和真空老化对ＮＲ硫化胶结构和性能的影响,采用化学探测剂脱硫的方法测定了老化过程中ＮＲ硫化胶交联密度及交联键分布变化的情况,同时测定了硫化胶的力学性能和动态性能随时间变化的情况。结果显示,热空气老化使硫化胶的交联密度增加,但力学性能损失严重,原因是主链氧化断裂。真空老化使ＮＲ硫化胶交联密度略微降低,但力学性能保持良好,类似于硫化返原。热空气老化使ＮＲ硫化胶的动态性能改善,而真空老化后     

Polyhedral oligomeric silsesquioxane-reinforced polyurethane acrylate

Hybride nanocomposite films of polyhedral oligomeric silsesquioxane (POSS) and polyurethane acrylate (PUA) were prepared by introducing POSS into PUA by free-radical photopolymerization, to enhance thermo-mechanical properties of PUA. The addition of POSS to PUA resulted in increases in the following properties: elasticity, glass transition temperature, thermal stability and dimensional stability. With increasing POSS content, the elastic modulus and thermal stability of PUA films increased due to an increased crosslinking density and the reinforcing effect of POSS particles on the PUA, whereas the surface free energies of these films decreased. The water contact angle against water increased due to the enhancement of the hydrophobicity of the polymer surface, caused by the low surface energy of POSS molecular. However, at high POSS content the mechanical properties of the films were decreased, as a result of aggregation of the POSS particles.     

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.     

Reactive supercritical fluid extrusion for development of moisture resistant starch‐based foams

The main objective of this work was to reduce barriers that prevent the usage of starch‐based foams by understanding the effect and the sequence of dual‐modification of crosslinked (XL) and acetylated (Ac) starch in one continuous supercritical fluid reactive extrusion (SCFX) process on wetting properties, physicochemical properties, and cellular structure of solid foam. The starch was reacted with epichlorohydrin (EPI) and acetic anhydride (Ac) under alkaline conditions in a twin‐screw extruder in the presence of supercritical carbon dioxide (SC‐CO₂). An increase in EPI concentration from 0.00 to 3.00% increased the degree of crosslinking as measured by DSC and confirmed by the quantification of the glucose units in the solution after acid hydrolysis. We observed a reduction of the glucose units from 93.07% for 0.00% EPI to 6.73% when 3.00% EPI was added. With crosslinking/acetylation processing, contact angle was higher for modified starches, indicating that chemical treatments induced dramatic changes in their surface polarity. Compared with native, the contact angle for dual modified starch increased from 43.1° to 91.7° which indicated their lower wettability. The addition of SC‐CO₂, EPI, and Ac to the formulation reduced the density of the extrudates and increased the expansion ratio. The average cell size in the extrudate determined by scanning electron microscopy was also found to decrease from 150 to 34 μm by the addition of the two reagents. Moreover, the dual‐modification of starches provided more hardness and adhesiveness to the extrudates than was observed for the unmodified starches. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and characterization of vinyltrimethoxysilane and dicumyl peroxide–cured (ethylene propylene diene monomer)/polypropylene thermoplastic vulcanizates

The present investigation deals with understanding the influence of vinyltrimethoxysilane (VTMS) concentration on the mechanical, thermal, thermomechanical, rheological, morphological, gel content, crosslinking density, and compression set properties of dynamically vulcanized ethylene propylene diene monomer (EPDM)/polypropylene (PP) (60/40, w/w) ‐based thermoplastic vulcanizates. It was determined that the values of crosslinking density, gel content, tensile strength, Young's modulus, elongation at break, and viscosity increased; whereas that of compression set, melting temperature, enthalpy of melting, crystallinity, and damping factor decreased with increased addition of VTMS in the EPDM/PP‐based thermoplastic vulcanizate. This is attributed to the physical crosslinking caused because of VTMS grafting on EPDM and chemical crosslinking induced by VTMS between PP and EPDM. This has been confirmed by Fourier‐transform infrared spectroscopy spectra, whereas the thermomechanical and scanning electron microscopy analysis confirmed increased compatibility between EPDM and PP on the addition of VTMS. J. VINYL ADDIT. TECHNOL., 23:312–320, 2017. © 2015 Society of Plastics Engineers     

新型紫外线固化环氧树脂/丙烯酸酯改性水性聚氨酯的合成与性能

合成了一种新型的具有高交联密度和优异涂膜性能的环氧树脂和丙烯酸酯同时改性的紫外线（UV）固化水性聚氨酯（UV-EP-AC-WPUD）。通过环氧基团与以异氰酸酯基团（-N=C=O）封端的聚氨酯预聚体之间的反应引入质量分数为4%的环氧树脂E-20。同时,通过聚氨酯链的-N=C=O与二元丙烯酸酯（PEDA）以及季戊四醇三丙烯酸酯（PETA）的羟基之间的反应引入碳碳双键（C=C）,C=C的含量达到4.65 meq·g-1。 质量分数为3%的光引发剂Irgacure 2959被用于引发涂膜中C=C的聚合,涂膜的凝胶含量在12 s UV辐射之后达到91%,意味着C=C的聚合和交联速度快,同时所得到的涂膜的交联度非常高,不溶于溶剂丙酮,测试表明环氧树脂和两种丙烯酸酯单体已经成功嵌入聚氨酯链中,涂膜具有优异的力学性能和化学性能。     

The effect of chemical crosslinking on the properties of Rotomolded high density polyethylene

In this study, high density polyethylene (HDPE) was combined with dicumyl peroxide (DCP) to produce crosslinked parts via rotational molding. The effect of DCP content (0.1–2.5 phr) on the crosslinking degree was investigated to determine its effect on the chemical, mechanical, physical, and thermal properties of HDPE. The gel content and crosslink density was found to increase with DCP content. These trends led to a reduction in the degree of crystallinity, melting, and crystallization temperature. Thermogravimetric analysis (TGA) showed that crosslinked HDPE (xHDPE) has higher thermal stability than the neat matrix in both air and nitrogen atmosphere. In addition, a direct relationship was observed between improved thermal resistance and higher impact strength. Finally, relationships between the tensile properties of xHDPE and the degree of crystallinity were observed, which were all controlled by the level of crosslinking. These results have the potential to advance the manufacturing of high performance materials suitable for a wide range of applications such as automotive parts, agricultural products, chemical storage tanks, large waste containers, and fuel tanks in general.     

Crosslinking of latex polymers

The physicomechanical properties and processes of thermal crosslinking of latex acrylic polymer films containing functional groups of different chemical nature were studied. Improvement of properties characteristic of latex copolymers containing methylolamide groups is explained by orientated location of hydrophilic groups on the surface of latex particles during emulsion copolymerisation, that, in its turn, leads to a more ordered arrangement of macrochains. An optimum content of methylolamide groups as regards crosslinking processes was established and explained by steric location of these groups on the surfaces of latex particles. A similar optimum is not observed for crosslinking by watersoluble resin of latex copolymers containing groups of hydrophobic glycidylmethacrylate.     

Effects of glycidyl methacrylate content and addition sequence on the acrylic latexes with carboxyl groups

Acrylic latexes with epoxy and carboxyl groups have been synthesized via a two-stage emulsion polymerization process. Different contents of glycidyl methacrylate (GMA) were introduced by three addition modes to copolymerize with methyl methacrylate, butyl acrylate, acrylic acid (AA) in the presence of K₂S₂O₈. To obtain stable latexes, NaHCO₃ was employed as a buffer to compensate for the acidity from the thermal dissociation of K₂S₂O₈, and triethylamine was used to neutralize the carboxyl acid from AA. The results showed that the stable latexes with core/shell structure were synthesized by this method, and higher GMA content or addition at earlier stage led to forming the latexes with higher content of coagulum and bigger sized particles. During the formation of films, the polymer epoxy groups underwent the crosslinking reaction with carboxyl acid. When the GMA content increased or GMA was introduced at a later stage, high crosslinking extent was formed in the films. As a result, the crosslinking provided the films with improved water resistance, chemical resistance, tensile strength, hardness, abrasion resistance, and thermal stability.     

葡萄糖改性水性聚氨酯的合成与表征

采用预聚体合成法,以二羟甲基丙酸（DMPA）、葡萄糖（PG）为亲水扩连剂和交联剂制备一种水性聚氨酯乳液。利用FTIR对胶膜结构进行表征,证实葡萄糖已引入聚氨酯主链。TG分析得出PG改性后的聚氨酯胶膜热稳定性增强。研究了PG用量对该聚氨酯胶膜力学性能的影响,结果表明：随着PG用量的增加,胶膜力学强度得到改善。当PG的用量由0增加至4.68%时,断裂伸长率从529.9%降至276.4%,拉伸强度从10.9 MPa增加至24.2 MPa。     

Poly(vinyl alcohol) films crosslinked by glutaraldehyde under mild conditions

The use of mild conditions to perform the entrapment of biomolecules in polymeric matrices is a crucial step in a broad range of applications as biosensors, biocarrier‐mediated facilitated transport membranes, and drug‐controlled release devices. In this study, we investigated the crosslinking of poly(vinyl alcohol) (PVA) by glutaraldehyde in the absence of an acid catalyst and organic solvents to improve the water resistance of the hydrophilic biocompatible polymer. Glutaraldehyde was chosen as the crosslinking agent because it favors the intermolecular reaction with PVA and is able to bind nonspecifically to proteins. The effects of the temperature and glutaraldehyde content on the thermal and structural properties of the PVA films were examined. Membranes prepared at 40°C showed a maximum crosslinking density for low glutaraldehyde content namely, 0.04 wt % in the spreading solution. Higher amounts of the crosslinker led to the branching of PVA. The increase in membrane thermal properties and reduction in crystallinity were ascribed to the crosslinking treatment, which was confirmed by Fourier transform infrared analysis. The oxygen permeability of the films was reduced up to 2.7 times, which indicated that the crosslinking of the polymer was successfully accomplished. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of crosslinking density on structure and properties of interpenetrating polymer networks from polyurethane and nitroguar gum

Semi‐interpenetrating polymer networks (semi‐IPNs) of castor oil‐based polyurethane prepolymer and nitroguar gum (NGG) with different crosslinking density of the PU network, coded as UNG films, were prepared through varying the trimethanol propane (TMP)/1,4‐butanediol (BDO) molar ratios in the chain extender mixture. The effects of crosslinking density on the structure and properties of the UNG films was investigated by attenuated total reflection Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical thermal analysis, scanning electron microscopy, crosslinking density measurements, solvent‐extracting tests, and tensile tests. The experimental results revealed that incorporation of TMP crosslinker into the hard segments of polyurethane resulted in a decrease in the aggregation of hard segments. With an increase of the TMP/BDO molar ratios, the semi‐IPN films exhibited the higher crosslinking density, glass temperature (T_g), stiffness, and tensile strength (σ_b). Furthermore, the experimental results also indicated that NGG restricted the formation of crosslinking networks when the TMP content is relatively high, which led to the negative deviation of the theoretically predicted crosslinking density and Dibenedetto's equation. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Effects of crosslinking agents on the physical properties of polyimide/amino‐functionalized graphene oxide hybrid films

The effects of crosslinking agents (crosslinkers) on polyimide (PI)/graphene oxide (GO) hybrid films were extensively investigated. The surface of GO was modified with amino groups using 4‐aminobenzylamine to improve compatibility with pyromellitic dianhydride/4,4′‐oxydianiline PI, and two kinds of crosslinkers were used: tris(4‐aminophenyl)amine and 1,3,5‐triazine‐2,4,6‐triamine (melamine). The mechanical, thermal and optical properties of the PI hybrid films were investigated. In particular, the transparency and physical properties of the PI hybrid films containing amino‐functionalized GO with homogeneous dispersion were improved. As the content of the crosslinker increased, a crosslinking network was formed between the PI chains, and the stiffness of the hybrid films was increased. The glass transition temperature, heat resistance and mechanical properties were also enhanced. The PI hybrids prepared with a rigid crosslinker exhibited higher optical transparency due to the reduction of the intermolecular charge transfer interactions with increasing interchain spacing between the PI chains. © 2018 Society of Chemical Industry     

Microstructure and properties of poly(urethane-siloxane)s based on hyperbranched polyester of the fourth pseudo generation

Poly(urethane-siloxane) networks based on hydroxyethoxy propyl terminated poly(dimethylsiloxane) (PDMS) as the soft segment and 4,4′-methylenediphenyl diisocyanate (MDI) and two hyperbranched polyesters with different core as the hard segments were characterized by swelling experiments, thermal analyses (DSC and TG), thermomechanical analysis (DMTA), X-ray scattering studies, SEM and AFM analyses, water contact angle and water absorption measurements, as well as surface free energy determination. From these studies, structure–property relationships were elucidated. Hyperbranched polyesters based on 2,2-bis(hydroxymethyl)propionic acid and ethoxylated pentaerythritol or di-trimethylolpropane as core (BH-40 and HBP-4) were used as crosslinkers for the samples of different series. Both series are composed of samples having different PDMS (i.e., soft segment) content. The crosslinking density and extent of hydrogen bonding showed an influence on the polyurethane (PU) properties. It was found that higher crosslinking density and better thermal stability of PUs based on BH-40 compared to HBP-4 based PUs are due to the less dense structure of BH-40. DMTA experiments revealed that the networks exhibit two glass transition temperatures, of the soft and hard segments, and one secondary relaxation process. The crosslinking density and extent of the microphase separation increased and thermomechanical properties were improved with decreasing content of PDMS. With increasing PDMS content, the surface of the polyurethane networks became more hydrophobic, the surface free energy decreased and thermal stability was improved. The obtained results revealed that synthesized PUs have good thermal and thermomechanical properties, which can be tailored for the potential use in the coating technology by changing the type of hyperbranched polyester or PDMS content.     

Effect of cure conditions on Probimide 32 polyamide-imide

We report on a curing study of Probimide 32, a preimidized polyamide-imide. The polymer was in a solution of N-methyl pyrrolidone (NMP) and xylene and was spun cast or doctor-bladed to form films for study. The films were cured by drying under a variety of conditions to effect solvent removal. We characterized the effects of cure by thermogravimetric analysis, dynamic mechanical analysis, Fourier transform infrared spectroscopy, and differential scanning calorimetry. Index of refraction was measured by waveguide prism coupling. Although the polymer did not require postprocessing thermal closure of its imide group, the physiochemical makeup of the system, and consequently, the properties of the Probimide 32 films, were highly dependent upon the curing temperature and environment. The properties/thermal stability improved as residual solvent was driven from the films. In the films hard baked at 300°C, the extent of thermally induced crosslinking was substantially greater in air-cured films than in nitrogen-cured films. The crosslinking markedly affected the properties and relaxation behavior of the material. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1113–1126, 1997     

Tensile,Swelling, and Oxidative Degradation Properties of Crosslinked Polyvinyl Alcohol/Chitosan/Halloysite Nanotube Composites

Glutaraldehyde (GA) crosslinked polyvinyl alcohol (PVA)/chitosan (CS)/halloysite nanotube (HNT) composite films were prepared using a wet casting method. The tensile, morphology, thermal degradation, swelling, moisture, and oxidative degradation properties of crosslinked composite films were carried out. The presences of crosslinking in the composite films were confirmed by FTIR result. The tensile strength of the crosslinked composite films increased up to 0.5 wt% of HNTs loading. Increasing HNTs reduced the thermal degradation, swelling, and moisture properties of crosslinked composite films reduced with the increase of HNTs content. Results also indicated that the crosslinked composite films were degraded using Fenton reagent.     

Crosslinking of plasticized PVC used in coated fabrics

Crosslinking is effective in improving the properties of plasticized poly(vinyl chloride) (PPVC), such as mechanical, chemical, and thermal resistance. In this study, the crosslinking was carried out using di‐tert‐butyl peroxide as an initiator in the presence of 1,1,1‐trimethylolpropane trimethacrylate (TMPTMA) as a crosslinking agent at two different curing temperatures. The degree of crosslinking was measured in terms of gel content and tensile strength. Upon increasing the amount of peroxide to an optimum level, the gel content and tensile strength increased to a maximum point, and above this level, the peroxide caused a slight decrease in crosslinking, which was due to the scission of PPVC chains during thermal degradation. J. VINYL ADDIT. TECHNOL., 2009. © 2009 Society of Plastics Engineers     

Chemical modification of cellulose acetate by allylation and crosslinking with siloxane derivatives

A new pathway to cellulose–siloxane hybrid materials was investigated. Allylated cellulose was prepared by chemical modification of cellulose acetate using three different procedures and was crosslinked afterwards by hydrosilylation in the presence of Karstedt's catalyst. Poly[dimethyl(methyl‐H)siloxane] with 25 mol% Si? H side groups and 1,1,3,3‐tetramethyldisiloxane were used as crosslinking agents in different ratios as regards the unsaturated component. The occurrence of the reaction was verified using Fourier transform infrared spectrometry following the reduction until disappearance of bands corresponding to Si? H and C?C bonds with the formation of new Si? C bonds that led to the crosslinking of the cellulose derivative. The reaction products were processed as films that were insoluble in common solvents. Surface (static contact angle, water vapour sorption capacity and swelling in various solvents), mechanical and thermal properties of the networks processed as films were investigated and the results were correlated with the reactant ratios. The crosslinking density was determined based on differential scanning calorimetry data. Copyright © 2012 Society of Chemical Industry