Surface modification of drawn gel-cast ultra-high molecular weight polyethylene films

Gel-spun ultra-high molecular weight polyethylene (UHMWPE) fibers have superior properties but their use in composite material applications is limited by their poor adhesion to polymer matrices. Previous studies have shown that etching improves the adhesion of epoxy to the fibers, but leads to a reduction in mechanical properties. The purpose of this research was to use uniaxially drawn gel-cast UHMWPE films as a model system since both films and fibers have a highly oriented fibrillar structural hierarchy. Etching has detrimental effects on the mechanical properties and crystallinity of these very thin films. The small amount of carbonyl and carboxyl groups added to the surface through etching raises the film's surface tension and enhances wetting by epoxy. Even though the unmodified film cannot be bonded with epoxy, the interlaminar shear strength between epoxy and the etched films approaches the cohesive strength of the epoxy. A combination of interfacial and UHMWPE cohesive failures is observed. The increase in adhesion is attributed to the slight increase in surface oxygen.     

Surface modification of UHMWPE fibers

Ultrahigh molecular weight polyethylene (UHMWPE) fibers have a high specific strength, high specific modulus, and outstanding toughness, but their poor adhesive properties has limited their use for composite material applications. In this research, the effects of chemical etching on the surface chemistry and topography have been explored using chromic acid, potassium permanganate, and hydrogen peroxide etching. The smooth surface observed on the as-received fiber was rich in ether and/or hydroxyl oxygen. This smooth surface resulted from the presence of an outer layer, a weak boundary layer, that was removed by all the etchants. A fibrillar structural hierarchy was revealed beneath this outer layer and the fiber was relatively unchanged by further etching. Chromic acid, the strongest etchant studied, produced a rough and oxidized UHMWPE surface with both ether and carbonyl oxygen. The combination of outer layer removal, roughness, and changes in oxygen bonding helps explain the improved adhesion on chromic acid etching in spite of the reduction in surface oxygen. Neither hydrogen peroxide nor potassium permanganate etching roughened or oxidized the surface to a great extent and neither yielded improved adhesion. © 1994 John Wiley & Sons, Inc.     

超高相对分子质量聚乙烯纤维的表面改性研究

选择乙烯-醋酸乙烯酯共聚物作表面改性剂,将其溶解在二甲苯中,对超高相对分子质量聚乙烯(UHMWPE)冻胶纤维进行萃取,然后经过多级热拉伸制得改性UHMWPE纤维。对冻胶纤维的萃取动力学、改性前后纤维的表面化学结构、表面粘结性能和力学性能进行了比较。结果表明:加入表面改性剂后,冻胶纤维的萃取除油速率变慢;纤维与树脂基体的粘结强度大大提高;纤维的力学性能略有下降。     

Interfacial evaluation of epoxy/carbon nanofiber nanocomposite reinforced with glycidyl methacrylate treated UHMWPE fiber

Interface interactions of fiber–matrix play a crucial role in final performance of polymer composites. Herein, in situ polymerization of glycidyl methacrylate (GMA) on the ultrahigh molecular weight polyethylene (UHMWPE) fibers surface was proposed for improving the surface activity and adhesion property of UHMWPE fibers towards carbon nanofibers (CNF)‐epoxy nanocomposites. Chemical treatment of UHMWPE fibers was characterized by FTIR, XPS analysis, SEM, and microdroplet tests, confirming that the grafting of poly (GMA) chains on the surface alongside a significant synergy in the interfacial properties. SEM evaluations also exhibited cohesive type of failure for the samples when both GMA‐treated UHMWPE fiber and CNF were used to reinforce epoxy matrix. Compared with unmodified composite, a ～319% increase in interfacial shear strength was observed for the samples reinforced with both 5 wt % GMA‐grafted UHMWPE and 0.5 wt % of CNF. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43751.     

Evaluation of Adhesion Property of UHMWPE Fibers/Nano-epoxy by a Pullout Test

Ultrahigh-molecular-weight polyethylene (UHMWPE) fibers have poor wetting and adhesion properties to polymer resins because of the inert surface of the fibers. In our previous study, a reactive nano-epoxy matrix, developed by making a modification on the matrix with reactive graphitic nanofibers (r-GNFs), showed improved wettability to UHMWPE fibers. In this work, fiber bundle pullout tests were conducted to evaluate the adhesion property between the UHMWPE fibers and the nano-epoxy matrices. Analysis of load-displacement curves from pullout tests shows that debonding initiation load and ultimate debonding load increased considerably, because of effective improvement of adhesion between the UHMWPE fibers and nano-epoxy matrix. Stress-controlled and energy-controlled models of interfacial debonding were applied for theoretical analyses. Results from ultimate IFSS, frictional shear stress, and critical energy-release rate are in good agreement with experimental results. Nano-epoxy matrix with 0.3 wt% r-GNFs shows effective improvement in terms of adhesion property between UHMWPE fiber and epoxy.     

超高相对分子质量聚乙烯纤维的表面改性研究

选择乙烯-醋酸乙烯酯共聚物作为表面改性剂,将其溶解在二甲苯中制成复合萃取液,对超高相对分子质量聚乙烯(UHMWPE)冻胶纤维进行萃取,经干燥和超倍拉伸制得表面改性UHMWPE纤维。对改性前后纤维的表面化学结构、结晶性能、表面粘接性能和力学性能进行了比较。结果表明:加入表面改性剂后,纤维表面引入了极性基团,结晶形态不变,纤维与树脂的抗界面剪切强度大大增加,纤维的力学性能变化不大。     

Two‐stage drawing process to prepare high‐strength and porous ultrahigh‐molecular‐weight polyethylene fibers: Cold drawing and hot drawing

High‐strength and porous ultrahigh‐molecular‐weight polyethylene (UHMWPE) fibers have been prepared through a two‐stage drawing process. Combined with tensile testing, scanning electron microscopy, and small‐angle X‐ray scattering, the mechanical properties, porosity, and microstructural evolution of the UHMWPE fibers were investigated. The first‐stage cold drawing of the gel‐spun fibers and subsequent extraction process produced fibers with oriented lamellae stacks on the surface and plentiful voids inside but with poor mechanical properties. The second‐stage hot drawing of the extracted fibers significantly improved the mechanical properties of the porous fibers because of the formation of lamellar backbone networks on the surface and microfibrillar networks interwoven inside to support the voids. With various processing conditions, the optimized mechanical properties and porosity of the prepared UHMWPE fibers were obtained a tensile strength of 1.31 GPa, a modulus of 10.1 GPa, and a porosity of 35%. In addition, a molecular schematic diagram is proposed to describe structural development under two‐stage drawing, including void formation and lamellar evolution. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42823.     

Fracture behavior of an epoxy/aluminum interface reinforced by sol–gel coatings

The strengths of epoxy/aluminum joints reinforced with a zirconium-silicon based sol–gel adhesion promoter were investigated using an ADCB (Asymmetric Double Cantilever Beam) wedge test. The fracture energies and loci of failure of these joints were shown to depend upon the mixity of the normal and shear modes of stress acting at the crack. The ADCB geometry enabled the crack to propagate along the epoxy/aluminum interfaces so that the effect of surface pretreatment and the processing conditions of the adhesion promoter on adhesion strength could be directly evaluated. The dry strength of these joints depends on the thickness of the sol–gel film derived from different concentrations of the precursors. Thinner films are more fully crosslinked and thus give higher adhesion strengths than those obtained with thicker films. The differences in the wet strengths of the sol–gel reinforced joints for various surface pretreatments suggest that the sol–gel films are subject to moisture degradation with certain surface pretreatments. The loci of failure of many of these joints alternate between the sol–gel/aluminum and epoxy/sol–gel interfaces. This behavior is similar to that observed more generally in adhesively-bonded joints tested in DCB (Double Cantilever Beam) geometry. The brittle versus ductile behavior associated with the failure process reveals important information about how the sol–gel films affect the adhesion strength.     

EVA共混改性UHMWPE纤维的表面性能

以乙烯-醋酸乙烯酯共聚物(EVA)作为共混改性剂,将其溶解在超高相对分子质量聚乙烯(UHMWPE)纺丝溶液中,制得共混改性UHMWPE冻胶纤维;对改性UHMWPE冻胶纤维进行萃取,干燥和热拉伸制得改性UHMWPE纤维;研究了改性前后纤维的结构与性能.结果表明:共混改性后UHMWPE纤维表面引入了极性基团,纤维与树脂基体...     

基于NOL环的高性能纤维与环氧树脂的匹配性研究

纤维与树脂的界面对复合材料的整体力学性能有着显著的影响。基于NOL环的宏观力学测试一般被用来反映复合材料的界面粘结性能,因此适用于评价纤维与树脂之间的宏观力学性能匹配性。为了探究高性能碳纤维T700SC、T800HB及高强玻璃纤维与环氧树脂的宏观力学性能匹配性,本研究首先根据GB/T 1458—2008国家标准制备NOL环试样,再借助NOL环的拉伸和层间剪切强度测试分析了高性能纤维与环氧树脂不同匹配组合宏观力学性能差异的原因,并寻找出最佳匹配组合。结果表明:玻璃纤维与环氧树脂的界面存在最佳的粘结强度,而且不同粘结强度导致拉伸强度和破坏机理不同,而碳纤维复合材料界面性能较差,容易分层破坏;T800HB与环氧树脂的宏观力学匹配性优于T700SC,环氧树脂力学性能、碳纤维的表面微观结构与性质以及环氧树脂与碳纤维之间的相互作用关系是影响界面粘结性能的根本原因。该研究在高性能纤维单向复合材料的材料选择与设计方面具有现实意义。     

Wetting and adhesion behavior of armos fibers after dielectric barrier discharge plasma treatment

To investigate the influence of atmospheric plasma treatment on aramid fiber wetting and adhesion behavior, an air dielectric barrier discharge (DBD) was applied to the Armos aramid fiber surface at different discharge power densities. Dynamic contact angle analysis indicated that the total surface free energy was increased from 49.6 to 68.3 mJ/m 2 , an increment of 37.7%, whereas the single-fiber tensile strength testing showed that the mechanical properties of the Armos fibers were almost unaffected. With the enhancement of fiber surface wettability, the interlaminar shear strength, which was used to determine the interfacial adhesion in Armos-fiber-reinforced thermoplastic poly(phthalazinone ether sulfone ketone) composites, increased by 17.2% to 71.4 MPa. Scanning electron microscopy photos showed that the predominant failure mode of the composites changed from interface failure to matrix and/or fiber failure after the plasma treatment. Taken together, these results suggest that the air DBD plasma was an effective technique for improving the surface and interfacial performance of the Armos fibers without damaging their bulk properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Surface modification and physical properties of various UHMWPE‐fiber‐reinforced modified epoxy composites

Two surface modification methods—plasma surface treatment and chemical agent treatment—were used to investigate their effects on the surface properties of ultrahigh‐molecular‐weight polyethylene (UHMWPE) fibers. In the analyses, performed using electron spectroscopy for chemical analysis, changes in weight, and scanning electron microscope observations, demonstrated that the two fiber‐surface‐modified composites formed between UHMWPE fiber and epoxy matrix exhibited improved interfacial adhesion and slight improvements in tensile strengths, but notable decreases in elongation, relative to those properties of the composites reinforced with the untreated UHMWPE fibers. In addition, three kinds of epoxy resins—neat DGEBA, polyurethane‐crosslinked DGEBA, and BHHBP‐DGEBA—were used as resin matrices to examine the tensile and elongation properties of their UHMWPE fiber‐reinforced composites. From stress/strain measurements and scanning electron microscope observations, the resin matrix improved the tensile strength apparently, but did not affect the elongation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 655–665, 2007     

Nanoscale toughening of carbon fiber‐reinforced epoxy composites through different surface treatments

Interests in improving poor interfacial adhesion in carbon fiber‐reinforced polymer (CFRP) composites has always been a hotspot. In this work, four physicochemical surface treatments for enhancing fiber/matrix adhesion are conducted on carbon fibers (CFs) including acid oxidation, sizing coating, silane coupling, and graphene oxide (GO) deposition. The surface characteristics of CFs are investigated by Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, interfacial shear strength, and interlaminar shear strength. The results showed that GO deposition can remarkably promote fiber/matrix bonding due to improved surface reactivity and irregularity. In comparison, epoxy sizing and acid oxidation afford enhancement of IFSS owing to effective molecular chemical contact and interlocking forces between the fiber and the matrix. Besides, limited covalent bonds between silane coupling and epoxy matrix cannot make up for the negative effects of excessive smoothness of modified CFs, endowing them inferior mechanical properties. Based on these results, three micro‐strengthening mechanisms are proposed to broadly categorize the interphase micro‐configuration of CFRP composite, namely, “Etching” “Coating”, and “Grafting” modifications, demonstrating that proper treatments should be chosen for combining optimum interfacial properties in CFRP composites. POLYM. ENG. SCI., 59:625–632, 2019. © 2018 Society of Plastics Engineers     

Investigation of the ultradrawing properties of gel spun fibers of ultra‐high molecular weight polyethylene/carbon nanotube blends

The carbon nanotubes (CNTs) contents, ultrahigh‐molecular‐weight polyethylene (UHMWPE) concentrations and temperatures of UHMWPE, and CNTs added gel solutions exhibited significant influence on their rheological and spinning properties and the drawability of the corresponding UHMWPE/CNTs as‐prepared fibers. Tremendously high shear viscosities (ηs) of UHMWPE gel solutions were found as the temperatures reached 140°C, at which their ηs values approached the maximum. After adding CNTs, the ηs values of UHMWPE/CNTs gel solutions increase significantly and reach a maximum value as the CNTs contents increase up to a specific value. At each spinning temperature, the achievable draw ratios obtained for UHMWPE as‐prepared fibers prepared near the optimum concentration are significantly higher than those of UHMWPE as‐prepared fibers prepared at other concentrations. After addition of CNTs, the achievable draw ratios of UHMWPE/CNTs as‐prepared fibers prepared near the optimum concentration improve consistently and reach a maximum value as their CNTs contents increase up to an optimum value. To understand these interesting drawing properties of the UHMWPE and UHMWPE/CNTs as‐prepared fibers, the birefringence, thermal, morphological, and tensile properties of the as‐prepared and drawn fibers were investigated. Possible mechanisms accounting for these interesting properties are proposed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Properties of UHMWPE fiber-reinforced composites

Based on our previous work, a new thermosetting resin system, named PCH, has been developed to be used as the matrix of ultrahigh-molecular-weight polyethylene (UHMWPE) fiber composites in order to get improved interface bond and mechanical properties. In this work, UHMWPE fiber/PCH composites with different ratios of PCH/styrene were prepared and the impact resistance, dynamic mechanical properties, and dielectric properties of UHMWPE fiber/PCH composites were investigated. The interlaminar shear failure characteristic of composites was analyzed by introducing a series of energy indexes indicating the energy absorbed in interlaminar shear failure process, which show good correlation with interlaminar shear strength of samples. UHMWPE fiber/PCH composites have excellent impact property, and the impact strength can reach 140.8 kJ/m² as the ratio of PCH/styrene is 60/40. Dynamic mechanical analysis showed that UHMWPE fiber/PCH composites have high storage moduli (E′) and low dissipation factor (tan δ) and these properties are influenced by the interfacial adhesion. The dielectric property test demonstrated that UHMWPE fiber/PCH composites have low dielectric constant (2.20 < ε′ < 2.55) and dielectric loss tangent (1.50 × 10^?3 < tan δ < 1.81 × 10^?2) and show good stability in a large range of frequency and temperature.     

电子束辐射接枝对PAN基碳纤维的表面改性

采用电子束加速器辐射接枝方法对聚丙烯腈(PAN)基碳纤维进行表面改性,研究了接枝单体种类对接枝率及其环氧树脂基复合材料力学性能的影响,分析了辐射接枝前后PAN基碳纤维的表面形貌与化学结构以及其复合材料界面断口的形貌变化。结果表明:电子束辐射接枝改性的PAN基碳纤维表面粗糙度增加,表面活性官能团增多,与树脂的机械锲合作用增强,其树脂基复合材料断口表而较为平整;乙二胺/水溶液体系是辐射接枝改性的理想溶液,在200 kGy的电子束辐射下,PAN基碳纤维表面的接枝率为6.66%,复合材料的层间剪切强度提高了45.1%。     

Ultradrawing behavior of one- and two-stage drawn gel films of ultrahigh molecular weight polyethylene and low molecular weight polyethylene blends

The ultradrawing behavior of gel films of plain ultrahigh molecular weight polyethylene (UHMWPE) and UHMWPE/low molecular weight polyethylene (LMWPE) blends was investigated using one- and two-stage drawing processes. The drawability of these gel films were found to depend significantly on the temperatures used in the one- and two-stage drawing processes. The critical draw ratio (λ_c) of each gel film prepared near its critical concentration was found to approach a maximum value, when the gel film was drawn at an “optimum” temperature ranging from 95 to 105°C. At each drawing temperature, the one-stage drawn gel films exhibited an abrupt change in their birefringence and thermal properties as their draw ratios reached about 40. In contrast, the critical draw ratios of the two-stage drawn gel films can be further improved to be higher than those of the corresponding single-stage drawn gel films, in which the two-stage drawn gel films were drawn at another “optimum” temperature in the second drawing stage after they had been drawn at 95°C to a draw ratio of 40 in the first drawing stage. These interesting phenomena were investigated in terms of the reduced viscosities of the solutions, thermal analysis, birefringence, and tensile properties of the drawn and undrawn gel films. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 149–159, 1998     

A New Surface Etching Method Using MnO2/H2SO4 Colloid for Adhesion Improvement of Epoxy Polymer

Abstract

A new surface etching method using MnO₂/H₂SO₄ as the etchant to improve the adhesion between an epoxy polymer surface and a metallic layer, was studied. The effects of bath temperature, etching time and H₂SO₄ concentration on the surface topography and chemical properties were investigated. After the etching treatment of the MnO₂–H₂SO₄ colloid, not only did the surface roughness increase remarkably, but also the surface of epoxy became hydrophilic and the contact angle of the epoxy surface was also decreased from 93.5° to about 8.0°. The X-ray photoelectron spectroscopy analysis indicated that as a result of the etching treatment, hydroxyl, carbonyl and carboxylic acid groups formed on the epoxy surface. The adhesion strength was markedly enhanced with the appropriate etching treatment, which was attributed to the improvement of the surface roughness and the increased hydrophilicity.     

Dynamic mechanical properties of the chemical oxidation on UHMWPE fibers for improved adhesion to epoxy resin matrix

The improved adhesion of an ultrahigh molecular weight polyethylene (UHMWPE) fiber to an epoxy from applying polypyrrole (PPy) was investigated using chemical oxidation polymerization. The interfacial shear strength of the PPy-treated fiber/epoxy was enhanced by 280%. Such an improvement was verified in the previous research using a pull-out test. Dynamic mechanical analysis (DMA) and a morphological examination were performed to evaluate the characteristics of the molecular motions of the UHMWPE fiber/PPy/epoxy composites. Two composite materials, a UHMWPE fiber/PPy and a UHMWPE fiber/PPy/epoxy, were tested by DMA. The results show that both the α_c transitions of the PPy-treated fibers and its composites shift toward higher temperature. In the SEM photos of the UHMWPE fiber/PPy, a very clear roughening effect on the surface of PPy-treated UHMWPE fiber was also observed, which contributes much to the modification of the interface to the epoxy. The results show that an adhesion improvement mechanism for the PPy-treaded UHMWPE fiber is due to the surface roughening effect and the intermolecular interaction. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1387–1395, 1998     

Improvement of Interfacial Adhesion of Glass Fiber/Epoxy Composite by Using Plasma Polymerized Glass Fibers

This study intends to produce plasma polymer thin films of γ-glycidoxypropyltrimethoxysilane (γ-GPS) on glass fibers in order to improve interfacial adhesion of glass fiber-reinforced epoxy composites. A low frequency (LF) plasma generator was used for the plasma polymerization of γ-GPS on the surface of glass fibers at different plasma powers and exposure times. X-ray photoelectron spectroscopy (XPS) and SEM analyses of plasma polymerized glass fibers were conducted to obtain some information about surface properties of glass fibers. Interlaminar shear strength (ILSS) values and interfacial shear strength (IFSS) of composites reinforced with plasma polymerized glass fiber were evaluated. The ILSS and IFSS values of non-plasma polymerized glass fiber-reinforced epoxy composite were increased 110 and 53%, respectively, after plasma polymerization of γ-GPS at a plasma power of 60 W for 30 min. The improvement of interfacial adhesion was also confirmed by SEM observations of fractured surface of the composites.