Wetting of oriented and etched ultrahigh molecular weight polyethylene

Highly oriented gel‐spun ultrahigh molecular weight polyethylene (UHMWPE) fibers possess many outstanding properties desirable for composite materials but their adhesion to such matrices as epoxy is poor. This article describes the combined effects of drawing and surface modification on the bulk and surface properties of gel‐cast UHMWPE films emphasizing the effects of etching on both undrawn and drawn films. Drawing the films yields a fibrillar structural hierarchy similar to UHMWPE fibers and a significant increase in orientation, melting point, modulus, and strength. The effects of drawing on bulk properties were more significant than those of etching. The poor adhesion of epoxy to the smooth, fibrillar, and relatively nonpolar drawn film surface improves significantly with oxidization and roughening on etching. The interlaminar shear failure occurred cohesively in the UHMWPE, and thus the interlaminar shear failure strength was greater for the drawn UHMWPE with its greater tensile strength. Nitrogen plasma etching yielded the best results, both removing any low molecular weight surface layer and etching the UHMWPE beneath. Oxygen plasma etching enhanced wetting but was too harsh, causing extensive surface degradation and a significant reduction in mechanical properties. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 405–418, 1999     

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.     

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.     

Surface modification of UHMWPE fibers by means of polyethylene wax grafted maleic anhydride treatment

A novel surface modification method for ultrahigh molecular weight polyethylene (UHMWPE) fibers to improve the adhesion with epoxy matrix was demonstrated. Polyethylene wax grafted maleic anhydride (PEW‐g‐MAH) was deposited on the UHMWPE fibers surface by coating method. The changes of surface chemical composition, crystalline structure, mechanical properties of fiber and composite, wettability, surface topography of fibers and adhesion between fiber and epoxy resin before and after finishing were studied, respectively. The Fourier transform infrared spectroscopy spectra proved that some polar groups (MAH) were introduced onto the fiber surface after finishing. The X‐ray diffraction spectra indicated that crystallinity of the fiber was the same before and after finishing. Tensile testing results showed that mechanical properties of the fiber did not change significantly and the tensile strength of 9 wt % PEW‐g‐MAH treated fiber reinforced composite showed about 10.75% enhancement. The water contact angle of the fibers decreased after finishing. A single‐fiber pull out test was applied to evaluate the adhesion of UHMWPE fibers with the epoxy matrix. After treatment with 9 wt % PEW‐g‐MAH, a pull‐out force of 1.304 MPa which is 53.59% higher than that of pristine UNMWPE fibers was achieved. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46555.     

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     

Mechanical properties of surface‐modified ultra‐high molecular weight polyethylene fiber reinforced natural rubber composites

The mechanical properties of ultra‐high molecular weight polyethylene (UHMWPE) fibers reinforced natural rubber (NR) composites were determined, and the effects of fiber surface treatment and fiber mass fraction on the mechanical properties of the composites were investigated. Chromic acid was used to modify the UHMWPE fibers, and the results showed that the surface roughness and the oxygen‐containing groups on the surface of the fibers could be effectively increased. The NR matrix composites were prepared with as‐received and chromic acid treated UHMWPE fibers added 0–6 wt%. The treated UHMWPE fibers increased the elongation at break, tear strength, and hardness of the NR composites, especially the tensile stress at a given elongation, but reduced the tensile strength. The elongation at break increased markedly with increasing fiber mass fraction, attained maximum values at 3.0 wt%, and then decreased. The tear strength and hardness exhibited continuous increase with increasing the fiber content. Several microfibrillations between the fiber and NR matrix were observed from SEM images of the fractured surfaces of the treated UHMWPE fibers/NR composites, which meant that the interfacial adhesion strength was improved. POLYM. COMPOS., 38:1215–1220, 2017. © 2015 Society of Plastics Engineers     

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。     

Effects of fiber surface chemistry and roughness on interfacial structures of electrospun fiber reinforced epoxy composite films

This work reported the effect of surface chemistry and roughness of electrospun fibers on fiber/matrix interfacial structures and the resultant macroscopical properties of composite films. Three types of fibrous mats composed of ultrafine fibers, that is, cellulose acetate (CANM), polyurethane (PUNM), and cellulose acetate/polyurethane composite (CAPUNM) were fabricated through electrospinning. CA fiber surfaces were rough with many hydroxyl groups; PU fiber surfaces were smooth, whereas CAPU composite fibers exhibited cocontiuous structure with rough surfaces. The fiber‐reinforced epoxy composite films were prepared by the solution impregnation method. The fractured surfaces of the composites were analyzed by scanning electron microscopy. Severe interfacial debonding and fiber pullouts were observed for PUNM/epoxy composites, while strong interfacial adhesion was formed for CANM/epoxy and CAPUNM/epoxy composites. The interfacial structure played important roles in the visible light transmittance of the composite films. For example, CANM/epoxy films showed the best optical property, whereas PUNM/epoxy films displayed the poorest light transmitting property and were translucent. The interfacial structure also affected the mechanical properties of the composites. The mechanical strength of fibrous mats followed an increasing order of CANM < CAPUNM < PUNM, but the mechanical strength of the composite films was in a reverse order, that is, CANM/epoxy > CAPUNM/epoxy > PUNM/epoxy. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

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     

Surface modification of ultra-high molecular weight polyethylene fibers by γ-radiation-induced grafting

A technique for grafting acrylic polymers on the surface of ultra-high molecular weight polyethylene (UHMWPE) fibers utilizing ⁶⁰Co gamma radiation at low dose rates and low total dose has been developed. Unlike some of the more prevalent surface modification schemes, this technique achieves surface grafting with complete retention of the exceptional UHMWPE fiber mechanical properties. In particular, poly(butyl acrylate) and poly(cyclohexyl methacrylate) were successfully grafted onto UHMWPE fibers with no loss in tensile properties. The surface and tensile properties of the fibers were evaluated using Fourier transform infrared/photoacoustic spectroscopy (FTIR/PAS), X-ray photoelectron spectroscopy (XPS), and tensile tests. The reinforcement efficiency of untreated, polymer-grafted, and plasma-treated UHMWPE fibers in polystyrene and a poly(styrene-co-butyl acrylate-co-cyclohexyl methacrylate) statistical terpolymer was characterized using mechanical tensile tests. The thermoplastic matrix composites were prepared with 4 wt% discontinuous (10 mm), randomly distributed UHMWPE fibers. An approximate 30% increase in composite strength and modulus was observed for poly(cyclohexyl methacrylate)-grafted fibers in the terpolymer and polystyrene matrices. A comparable improvement was realized with the plasma-treated fibers. On the other hand, poly(butyl acrylate) grafts induced void formation, i.e. energy dissipation through plastic deformation and volume expansion at the fiber/matrix interface in terpolymer composites. The latter resulted in a 75% increase in the elongation to failure. The effect of polymer grafts on fiber/matrix adhesion is discussed in terms of the graft and matrix chain interactions and solubility, graft chain mobility, and fracture surface characteristics as determined by scanning electron microscopy (SEM).     

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.     

UHMWPE纤维高强度绳索的研究

研究了纤维捻度、粘结剂对超高分子量聚乙烯(UHMWPE)纤维力学性能的影响及浸胶UHMWPE纤维表面的耐磨性能。UHMWPE纤维的断裂强力随着纤维捻度的增加而下降；纤维表面浸胶处理后断裂强力提高，当UH—MWPE纤维中改性氯丁胶或聚氨酯粘结剂的合量为6％时，其断裂强力增加17．2％或13．9％。经聚氨酯粘结剂处理的UHMWPE纤维表面的耐磨性能最好。     

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.     

Control of the interfacial properties of ultrahigh‐molecular‐weight polyethylene/magnesium hybrid composites through use of atmospheric plasma treatment

This work aims to explore the use of lightweight magnesium alloys as an advanced composite material in conjunction with lightweight thermoplastic materials, such as ultrahigh‐molecular‐weight polyethylene (UHMWPE). High throughput, environmentally friendly, atmospheric plasma treatment methods were used to control the interfacial properties and improve the adhesion behavior of metallic/UHMWPE composites. Helium‐oxygen dielectric barrier discharges were used, and the plasma‐activated UHMWPE surfaces were characterized through analytical and mechanical characterization methods. Oxygen content on the treated polymer surfaces increased 18.1–36.0%. A reduction in silicon content combined with characterization through microscopy reveal a preference for the attack of the matrix over the polyethylene fibers. Wetting angles for the treated samples decreased as much as 53.7%. Treated UHMWPE/Mg hybrid samples exhibited lap shear strengths up to 113.7% greater than the control. Both the plasma‐induced surface functionalization with oxygen‐containing polar groups (carboxyl, carbonyl, and hydroxyl groups) and the preferential mild etching of the polymer matrix over the fibers lead to the improvement in adhesion. POLYM. COMPOS., 2012. © 2011 Society of Plastics Engineers     

Sulfonation of polymer surfaces - I. Improving adhesion of polypropylene and polystyrene to epoxy adhesives via gas phase sulfonation

A new method for surface treating polymers and polymer composites based on gas phase sulfonation has been shown to quickly and effectively increase wettability and adhesion to epoxy. A gas mixture containing a low concentration of sulfur trioxide in nitrogen (～ 1% v/v) was used to treat the surfaces of polypropylene and polystyrene films. The sulfonated surfaces were then neutralized with ammonium hydroxide. The effectiveness of sulfonation on the adhesion of these polymers to an epoxy adhesive was investigated using mechanical testing of sandwich lap-shear specimens. The lap-shear adhesive joint strength of epoxy to sulfonated polypropylene was compared with polypropylene treated with currently accepted surface treatments including chromic acid etching and flame treatment. Sulfonation greatly improves the adhesion of polypropylene to epoxy compared with other surface treatment techniques as measured by lap-shear strength. An optimum sulfonation treatment level was shown to exist for polypropylene. For polystyrene surfaces, it was shown that while sulfonation immediately increased wettability, it did not greatly improve its adhesion to epoxy; it did, however, significantly reduce the scatter in the ultimate strength values. Excess sulfonation treatment reduced the lap-shear strength for both polymers. X-ray photoelectron spectroscopic examination of the locus of failure of tested joints has shown that failure occurs in a weak boundary layer for these surface-treated polymers.     

Mechanisms for the Improvement in Interfacial Adhesion Between UHMWPE Reinforcement and Nano-epoxy Resins with Reactive Graphitic Nanofibers

Previously developed nano-epoxy matrices with reduced viscosity showed both substantially enhanced mechanical properties and interfacial adhesion with ultra-high molecular weight polyethylene (UHMWPE) fibers vis-à-vis pure epoxy. In this work, mechanisms for the improvement in the interfacial adhesion were investigated. Atomic Force Microscopy and Energy Dispersive X-ray with Scanning Electron Microscopy analyses indicated that improved performance of the UHMWPE fiber composites with the nano-epoxy containing reactive graphitic nanofibers (r-GNFs) is attributed to mechanical interlocking and a diffusion mechanism. The nano-epoxy with the 'liquid nano-reinforcement' resulting in reduced viscosity provided better wettability, diffusion capability and reinforcing effect, which produced an effective improvement in the adhesion properties.     

UHMWPE共混改性HDPE薄膜性能的研究

采用中等摩尔质量聚乙烯（MMWPE）首先对超高摩尔质量聚乙烯（UHMWPE）进行改性，然后通过两步共混法制备了HDPE／UHMWPE共混吹塑薄膜，研究了共混物的力学、流变性能以及MMWPE对UHMWPE力学和流变性能的影响。实验结果表明，当改性UHMWPE中的MMWPE的质量分数为40％时，改性UHMWPE的力学性能下降不大，而流变性能大大改善。两步法制得的HDPE／UHMWPE薄膜表面的晶点明显减少，比一步法得到的薄膜的拉伸强度和撕裂强度分别提高了20％和12％，比纯HDPE的分别提高45％和21％。     

Surface modification of spectra™-900 polyethylene fibers using RF-plasma

RF-plasma polymerization and bonding of allylamine onto ultrahigh molecular weight polyethylene (UHMWPE) “Spectra™-900” is described using an inductively coupled plasma reactor. This process was found to enhance the interfacial strength between the fibers (Spectra-900) and room-temperature-cured epoxy matrix up to fivefold. Fibers covalently coated with allylamine plasma showed no loss in tensile strength, while argon gas plasma pretreatment of the same fibers caused up to 10% reduction in tensile strength depending on the energy and duration of the treatment. Optimum treatment was attained through a short argon plasma etching (15 s), followed by allylamine polymerization and coating for 3 min. The coating process was found to protect the fiber surface from etching by plasma ion bombardment. A loss of 19% of the original diameter was found during the 15 s precoating etching with argon plasma, indicating the sensitivity of the fiber structure to plasma etching.     

Adhesion of Graphite Fibers to Epoxy Matrices: I. The Role of Fiber Surface Treatment

Adhesion between graphite fibers and epoxy matrices is a necessary and sometimes controlling factor in achieving optimum performance. Manufacturers' proprietary fiber surface treatments promote adhesion without providing a basic understanding of the fiber surface properties altered through their use. This study has combined fiber surface chemistry, morphology, interfacial strength measurements and fracture characterization in order to elucidate the role of surface treatments. The results of this investigation lead to the conclusion that surface treatments designed to promote adhesion to epoxy matrix materials operate through a two-part mechanism. First, the treatments remove a weak outer fiber layer initially present on the fiber. Second surface chemical groups are added which increase the interaction with the matrix. Increases in fiber surface area are not an important factor in promoting fiber-matrix adhesion. In some cases the upper limit to fiber-matrix interfacial shear strength is the intrinsic shear strength of the fiber itself.     

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。