Properties of hydrophilic chitosan network membranes by introducing binary crosslink agents

Summary In this investigation chitosan (CS) was crosslinked using mixtures of sulfosuccinic acid (SSA) and glutaraldehyde (GA) as the binary crosslinking agents to form hydrophilic chitosan network membranes. GA and SSA improve the tensile strength and contribute to hydrophilicity of the membranes, respectively. The membranes prepared by varying the crosslinking agent ratios are also characterized using FT-IR, X-ray diffraction, and tensile testing, and their swelling ratio and thermal properties were measured. Experimental results reveal that the contact angle of the membrane decreases from 84.54° to 69.83° and the maximum stress rises from 39.62 MPa to 133.66 MPa as the increase of the binary crosslinking agent content. These resultant membranes not only maintain its hydrophilicity and but also enhance the mechanical strength.     

Performance evaluation of silane crosslinking of metallocene‐based polyethylene–octene elastomer

Vinyl trimethoxysilane (VTMS) was grafted onto metallocene‐based polyethylene–octene elastomer (POE) using a free‐radical reaction of VTMS and dicumyl peroxide as an initiator, and then the grafted POE was crosslinked in the presence of water. The effects of VTMS concentration on crystallization behavior, mechanical properties, and thermal properties of POE before and after crosslinking were studied in this article. Multiple melting behaviors were found for POE after silane crosslinking by using DSC measurement. Degree of crystallization of silane‐crosslinked POE decreases from 18.0 to 14.3%, with increase of VTMS from 0 to 2.0 phr. Tensile strength of silane‐crosslinked POE reaches a maximum of 28.4 MPa when concentration of VTMS is 1.5 phr, while elongation at break is 487%. TG shows that the temperature of 10% weight loss for pure POE is 405°C, while for crosslinked POE with addition of 2.0 phr VTMS the value comes to 452°C, indicating that crosslinking significantly help improve the thermal stability of POE. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5057–5061, 2006     

Properties of crosslinked casein/waterborne polyurethane composites

Waterborne polyurethane (WPU) and casein (1 : 1 by weight) were blended at 90°C for 30 min, and then were crosslinked by adding 1–10 wt % ethanedial to prepare a series of sheets. Their structure and properties were characterized by using infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, dynamic mechanical analysis, and tensile testing. The results indicated that crosslinked blend sheets exhibited a certain degree of miscibility, and exhibited much higher tensile strength and water resistivity than did the WPU, casein, and the uncrosslinked blend from WPU and casein. When the ethanedial content was 2 wt %, the tensile strength and elongation at break of crosslinked sheets achieved 19.5 MPa and 148% in the dry state, and 5.0 MPa and 175% in the wet state, respectively. A 2 wt % content of ethanedial plays an important role in the enhancement of mechanical properties, thermal stability, and water resistivity of the blends of WPU and casein as a result of intermolecular crosslinking. This work provided a new protein plastic with good water resistivity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 332–338, 2004     

Profile extrusion and mechanical properties of crosslinked wood–thermoplastic composites

Challenges for wood‐thermoplastic composites to be utilized in structural applications are to lower product weight and to improve the long‐term load performance. Silane crosslinking of the composites is one way to reduce the creep during long‐term loading and to improve the mechanical properties. In this study, silane crosslinked wood‐polyethylene composites were produced by reactive extrusion and subsequently manufactured into rectangular profiles. The silane crosslinked composites were stored in a sauna at 90 °C to increase the degree of crosslinking. The toughness of the silane crosslinked composites was significantly higher than for the non‐crosslinked composites. Improved adhesion between the wood and polyethylene phases is most likely the reason for the improved toughness of the crosslinked composites. There was no significant difference in flexural modulus between the crosslinked and non‐crosslinked composites. In addition, impact testing showed that the impact strength of the crosslinked composites was considerable higher (at least double) than the non‐crosslinked. The effect of temperature on the impact strength of the composites indicated slightly higher impact strength at −30 °C than at 0° and at 25 °C, and then an incrase in impact strength at 60 °C. Crosslinking also reduced the creep response during short‐term loading. Moreover, scanning electron microscopy on the fracture surface of the crosslinked composites revealed good adhesion between the polyethylene and wood phases. POLYM. COMPOS. 27:184–194, 2006. © 2006 Society of Plastics Engineers     

Composites produced from waste plastic with agricultural and energy sector by-products

A three-stage route to chemically upcycle post-consumer poly(ethylene terephthalate) (PET) to produce high compressive strength composites is reported. This procedure involves initial glycolysis with diethylene glycol to produce a mixture (GPET) comprising oligomers of 2–7 terephthalate units followed by trans/esterification of GPET with fatty acid chains supplied by brown grease, an agricultural by-product of animal fat of relatively low nutritional or fuel value. This process yields PGB comprising a mixture of mono-terephthalate ester derivatives. The olefin units provided by unsaturated fatty acid chains in brown grease were crosslinked by an inverse vulcanization reaction with elemental sulfur to give composites GBS_x (x = wt% S, varied from 80%–90%). The compressive strengths of GBS₈₀ (27.5 ± 2.6 MPa) and GBS₉₀ (19.2 ± 0.8 MPa) exceed the compressive strength required of ordinary Portland cement (17 MPa) for its use in residential building foundations. The current route represents a way to repurpose waste plastic, energy sector by-product sulfur, and agricultural by-product brown grease to give high strength composites with mechanical properties suggesting their possible use to replace less sustainably sourced legacy structural materials.     

Mechanical and thermal properties of blends of low‐density polyethylene and ethylene vinyl acetate crosslinked by both dicumyl peroxide and ionizing radiation for wire and cable applications

Formulations of chemically crosslinked and radiation‐crosslinked low‐density polyethylene (LDPE) containing an intumescent flame retardant such as ammonium polyphosphate were prepared. The influence of blending LDPE with a poly(ethylene vinyl acetate) copolymer (EVA) and the effects of various coadditives, including polyethylene grafted with maleic anhydride (PEgMA), vinyl silane with boric acid, and talc, on the mechanical and thermal properties were investigated. Chemical crosslinking by dicumyl peroxide and crosslinking by ionizing radiation from an electron‐beam accelerator were both used and compared. Improved mechanical properties were observed by the partial replacement of LDPE with EVA. Similar mechanical or thermal properties were observed with coadditives such as PEgMA and vinyl silane with boric acid. The addition of a small amount of talc improved the tensile strength of the formulations. All crosslinked formulations showed good thermal stability on the basis of the retention of mechanical properties after thermal aging for 168 h at 135°C and a hot‐set test. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crosslinking benzotriazolylimides and polymeric materials on base of them

A new kind of crosslinking oligobenzotriazolylimides with terminal maleimide groups has been synthesized via an interaction of an excess of bismaleimides with 5,5′‐bisbenzotriazoles in melt. Conditions of obtaining these oligomers were optimized via the syntheses of model compounds. Oligomers, according to dynamic thermogravimetric analysis (DTGA), fuse at 135–160°C, crosslink at 175–250°C, and possess the high thermal stability in air up to 410°C. Using these oligomers as thermosetting binders or crosslinking agents, tough laminate plastics reinforced by a glass‐fiber cloth as well as crosslinked films on base of a linear polybenzimidazole (PBI) matrix were obtained. The plastics and the crosslinked films possess high mechanical characteristics. It has been proved that the crosslinked films on base of the PBI matrix are perspective precursors to design the phosphoric acid electrolyte membranes for the medium temperature fuel cells. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Silane grafting and moisture crosslinking of polypropylene

Peroxide initiated vinylsilane grafting of polypropylene in an intensive mixer, and the subsequent water crosslinking process were studied. Different concentrations of vinyl trimethoxysilane and dicumyl peroxide were used. The materials obtained after mixing in the rheocord were hot pressed at 190°C. The melt viscosity of the obtained sheets, the melting enthalpy and melting temperature (DSC, differential scanning calorimetry), the mechanical properties and the thermal decomposition behavior (TG, thermogravimetric analysis) were studied. No evidence of grafting during the rheocord processing was observed. Nevertheless, for the hot pressed sheets with concentrations higher than 4 phr of vinyl silane an important increase in the melt viscosity was observed. This increase agrees with the change observed in the mechanical properties, which show a maximum for the water crosslinked samples containing 4 phr of vinyl silane. The modulus increases by 39% at 90°C and 33% at 130°C, while the tensile strength rises by ～22% at both temperatures. The silane grafted water crosslinked samples show a more stable thermal behavior than both the silane grafted samples and the unmodified polypropylene.     

Toughening of trifunctional epoxy system. V. Structure–property relationships of neat resin

This work presents an investigation into the structure–property relationships of a cured highly crosslinked epoxy/amine resin system. The mechanical, physical, and thermal properties of the cured and postcured networks were measured and compared to the chemical structures. Crosslink density was shown to be dependent upon secondary amine conversion and it determined the glass transition temperatures, water uptake, density, toughness, and compressive strength. Other properties such as compressive modulus and yield stress were determined by more short‐range molecular motions. Curing at a temperature of 150°C was shown to be the minimum temperature required to “completely” cure the network and achieve optimum mechanical, physical, and thermal properties. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 237–248, 2000     

Preparation and characterization of a novel transparent flame retardant unsaturated phosphate ester polymer

A novel unsaturated phosphate ester (UPE) was synthesized with triethyl phosphate (TEP), ethylene glycol (EG), and α‐methylacrylic acid (MAA). The unsaturated phosphate ester polymer (PUPE) was prepared by bulk polymerization of UPE. The structure of UPE and PUPE series were confirmed by Fourier transform infrared and liquid chromatography‐mass spectrometry (LC‐MS). Due to the chain transfer during polymerization, a crosslinked network was successfully introduced into the polymers, as evinced by the results from extraction and dynamic mechanical analysis. PUPE series exhibited high transparency, good mechanical properties, thermal properties, and excellent fire retardancy. The transmittance of PUPE‐3 was up to 92%; the tensile strength and impact strength were 14.62 MPa and 30.5 kJ m^?2, respectively. The tensile strength of PUPE series was increased from 1.7 MPa to 35.5 MPa while impact strength was decreased with the increase of MAA ratio. The char yield of PUPE series reached 29.07 wt% by thermogravimetric analysis testing, which indicated that PUPE had excellent charring ability at high‐temperature insulated air and prevented heat conduction. PUPE‐3 had two glass transition temperatures (T_g) (113°C/139°C) as the crosslinking interaction restricts the polymer chain motion, and successfully passed UL‐94 V‐0 flammability rating and the LOI value reached 32%. POLYM. ENG. SCI., 59:E425–E431, 2019. © 2019 Society of Plastics Engineers     

戊二醛交联乙烯—乙烯醇非织造布的制备及研究

采用高压静电纺丝技术,以DMAc为溶剂,经戊二醛交联改性制备了戊二醛交联乙烯-乙烯醇(EVOH)非织造布。通过扫描电子显微镜(SEM)、热失重分析(TG)对其微观形貌、耐热性进行了研究,并分析了戊二醛交联EVOH非织造布的横向拉伸强度。结果表明:经戊二醛交联改性后,纤维直径变大,出现扭转和弯曲,并且发生了纤维间局部粘结现象;TG分析表明,经戊二醛交联改性后的EVOH非织造布的耐热性提高;戊二醛交联EVOH非织造布横向拉伸强度为97.90MPa,明显大于纯EVOH非织造布的横向拉伸强度。     

Mechanical and thermal insulation properties of isocyanate crosslinked resorcinol formaldehyde aerogel: Effect of isocyanate structure

In this article, the mechanical and thermal properties of resorcinol formaldehyde (RF) aerogels were improved using two different crosslinkers including hexamethylene diisocyanate (HDI) and methylene diphenyl diisocyanate (MDI). The crosslinking was performed after the aerogel drying process, with two concentrations of crosslinking agent. The formation of urethane linkages was investigated by Fourier transform infrared spectroscopy. The effect of crosslinking process and crosslinking agent type on the mechanical properties was analyzed by compression, bending, and impact tests. The improvement of mechanical strength was attributed to the neck thickness, which was studied by atomic force microscopic test. The results revealed that a higher improvement was obtained by increasing the crosslinking agent value. HDI crosslinked aerogel represented the highest strain-at-break and MDI-reinforced sample showed the highest strength. By crosslinking, the samples density was increased <59% and the reduced compressive strength was enhanced upto eight times. The effect of crosslinking on the thermal conductivity was explored. The increment of neck size and density enhanced the solid conductivity and, consequently, raised the thermal conductivity. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48196.     

AB‐type crosslinked polymer networks from vinyl terminated polyurethane and poly(methyl methacrylate)

Vinyl terminated polyurethanes (VTPUs) were prepared by endcapping isocyanate terminated prepolymers with vinylbenzyl alcohol (VBA). AB‐type crosslinked polymer (ABCP) networks were generated by crosslinking the telechelic polyurethane with methyl methacrylate (MMA) in the presence of 2,2′‐azobisisobutyronitrile (AIBN) as free radical initiator. The spectral, thermal and mechanical properties of ABCPs were studied using Fourier Transform IR, thermogravimetry, dynamic mechanical analysis and stress‐strain analysis. The FTIR results confirm the formation of VBA, TP and ABCPs. Thermal behaviour of crosslinked polymers showed no significant weight loss up to 300 °C, indicating improved thermal stability. Dynamic mechanical tests revealed confinement of phase separation and good damping behaviour for the crosslinked networks. Stress‐strain analysis showed that tensile strength increases with increasing amounts of methyl methacrylate. © 2001 Society of Chemical Industry     

Loop strength of spun collagen fibers

The effects of gultaraldehyde (GA) crosslinking, basic chromium sulfate (Cr) tanning, and thermal treatments on the loop strength of spun collagen fibers were studied. The loop test have been carried out using a piano wire as a model loop. The promotion of GA crosslinking led a significant decrease of the strength and elongation at break. On the other hand, the promotion of Cr tanning gave no change. These properties decreased with an increasing shear stress at bending region of loop. The improvement of these mechanical properties were realized by thermal treatments of both GA crosslinked and Cr tanned fibers. The thermal treatment temperature showed the maximum effect at 100°C. However, there was no effect of thermal treatment for the noncrosslinked fibers. The fracture morphology of Cr tanned fibers is characterized by longitudinal splitting along the fiber axis in the bending region, although the fracture morphology of noncrosslinked and GA crosslinked fibers can be characterized by transverse fracture. © 1996 John Wiley & Sons, Inc.     

Mechanical properties of crosslinked polyethylene

The mechanical properties of crosslinked polyethylene were studied in an extended range of test conditions in order to determine the recommended service conditions for articles made of crosslinked polyethylene. On the other hand, this study can clarify the advantages of crosslinked polyethylene against the unmodified polymer. In fact, the results referred in the literature concerning the changes of mechanical properties of polyethylene introduced by crosslinking are contradictory and cannot clearly distinguish the two types of polymer. The above study concluded that tensile tests at elevated temperatures (above 70°C) with low stresses (about 0.5 MPa) can clearly describe the effect of crosslinking on the mechanical properties of LDPE, i.e., an improvement at least for deformation and service life.     

Polyimide foams with ultralow dielectric constants

To explore ultralow dielectric constant polyimide, the crosslinked polyimide foams (PIFs) were prepared from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA), 4,4′‐oxydianiline (ODA), and 2,4,6‐triaminopyrimidine (TAP) via a poly(ester–amine salt) (PEAS) process. FTIR measurements indicated that TAP did not yield a negative effect on imidization of PEAS precursors. SEM measurement revealed the homogeneous cell structure. Through using TAP as a crosslinking monomer, the mechanical properties of PIFs could be improved in comparison with uncrosslinked BTDA/ODA based PIF. The crosslinked PIFs still exhibited excellent thermal stability with 5% weight loss temperatures higher than 520°C. In the field with frequency higher than 100 Hz, the dielectric constants of the obtained PIFs ranged from 1.77 to 2.4, and the dielectric losses were smaller than 3 × 10^?2 at 25–150°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1734–1740, 2006     

Mechanical properties of crosslinked polyurethane elastomers based on well‐defined prepolymers

This article presents research findings for selected mechanical properties of polyurethane elastomers. The studied elastomers were synthesized with the prepolymer‐based method with the use of controlled molecular weight distribution (MWD) urethane oligomers and with the classical single‐stage method. Prepolymers with defined MWDs were obtained with the use of a multistage method, that is, step‐by‐step polyaddition. To produce elastomers, isocyanate oligomers were then crosslinked with triethanolamine, whereas hydroxyl oligomers were crosslinked with 4,4′,4′′‐triphenylmethane triisocyanate (Desmodur RE). The tensile strength of the obtained elastomers ranged from 1.0 to 7.0 MPa, the ultimate elongation approached 1700%, the Shore A hardness varied from 40 to 93°, and the abrasion resistance index fell within 15–140. The effects of the types of raw materials used, the chemical structures, the production methods, and the supermolecular structures on the mechanical properties of the obtained polyurethane elastomers were examined. When the obtained findings were generalized, it was concluded that the structural changes in the polyurethanes, which were favorable for intermolecular interactions, improved the tensile strength, hardness, and abrasion resistance of the materials and impaired their ultimate elongation at the same time. More orderly supermolecular structures and, therefore, superior mechanical properties were found for polyurethane elastomers produced with the prepolymer method. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Properties of aminosilane grafted moisture curable poly(vinyl chloride) formulations

The reaction of plasticized PVC with [N-(2-amino ethyl)-3aminopropyl trimethoxy silane] yielded silane-grafted PVC that was crosslinked by a hydrolytic mechanism. It was found that crosslinking resulted in improvement of mechanical properties (tensile strength and elongation at break) specially at temperatures higher than 80°C. Properties at 130°C were substantially enhanced, showing a fourfold increase in ultimate tensile strength (UTS), and a twofold increase in elongation at break. There was a unique relationship between UTS at 130°C and gel content irrespective of processing conditions, with UTS starting to increase sharply around 30% gel content, and reaching a plateau at about 60%. Also, the softening temperature was improved. The crosslinked material had a higher softening temperature (up to 165°C, compared with 95°C for the compound without crosslinking agent), indicating that the hydrolytic crosslinking of PVC yielded a material with improved properties.     

Thermal and mechanical properties of poly(ε‐caprolactone) crosslinked with γ radiation in the presence of triallyl isocyanurate

Poly(?‐caprolactone) was crosslinked by γ radiation in the presence of triallyl isocyanurate. The influence of γ‐radiation crosslinking on the thermal and mechanical properties of poly(?‐caprolactone)/triallyl isocyanurate was investigated. Differential scanning calorimetry analyses showed differences between the first and second scans. Dynamic mechanical analysis showed an increase in the glass‐transition temperature as a result of the radiation crosslinking of poly(?‐caprolactone). Thermogravimetric analysis showed that γ‐radiation crosslinking slightly improved the thermal stability of poly(?‐caprolactone). The γ radiation also strongly influenced the mechanical properties. At room temperature, crosslinking by radiation did not have a significant influence on the Young's modulus and yield stress of poly(?‐caprolactone). However, the tensile strength at break and the elongation at break generally decreased with an increase in the crosslinking level. When the temperature was increased above the melting point, the tensile strength at break, elongation at break, and Young's modulus of poly(?‐caprolactone) were also reduced with an increase in the crosslinking level. The yield stress disappeared as a result of the disappearance of the crystallites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2676–2681, 2007     

Peroxide modification of poly(butylene adipate‐co‐succinate)

We attempted to introduce crosslinking into poly(butylene adipate‐co‐succinate) (PBAS) to improve the properties, such as the mechanical strength and elasticity, by a simple addition of dicumyl peroxide (DCP). Prior to curing, the thermal stability of PBAS was investigated. Above 170°C PBAS was severely degraded, and the degradation could not be successfully stabilized by an antioxidant. The PBAS was effectively crosslinked by DCP, and the gel fraction increased as the DCP content increased. A major structure of the crosslinked PBAS was an ester and aliphatic group. The tensile strength and elongation of PBAS were improved with an increasing content of DCP, but there was little affect on the tear strength. The biodegradability of crosslinked PBAS was not seriously deteriorated. A higher degree of crosslinking gave a lower heat of crystallization and heat of fusion. However, the melt crystallization temperatures of the crosslinked PBAS were higher than that of PBAS. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 637–645, 2001