Improvement of the interfacial compatibility between sugar cane bagasse fibers and polystyrene for composites

Sugar cane bagasse fibers were modified by surface treatments using either physical or chemical methods in order to improve their adhesion to polystyrene matrices. The surface treatment methods used were alkaline treatment, treatment with silane coupling agents, physical coating with polystyrene and grafting of polystyrene with and without crosslinker. Fiber modifications were monitored by Fourier Transform Infrared Spectroscopy (FTIR), Differential Thermal Analysis coupled with Thermogravimetric Analysis (DTA-TGA) and Scanning Electron Microscopy (SEM). On the other hand, the improvement of the adhesion between sugar cane modified fibers and polystyrene was assessed by micromechanical pull-out and by macromechanical Iosipescu tests. It was found, from Interfacial Shear Strength values (IFSS), that substantial improvements in fiber-matrix compatibility were achieved. According to micro- and macromechanical test results, the IFSS increased for all treated fibers as compared to non-treated fibers. Particularly, both the coating the fibers or grafting with polystyrene using crosslinker resulted in substantial adhesion improvement to the polystyrene matrix in comparison with the non-treated fibers and fibers treated by alkaline and silane methods only. Polym. Compos. 25:134–145, 2004. © 2004 Society of Plastics Engineers.     

Effect of silane treatment on the Curaua fibre/polyester interface

ABSTRACT

Good adhesion at fibre/matrix interface of lignocellulosic fibres is crucial when substituting synthetic fibres in polymer composites. The great variability presented by those fibres requires diverse characterisation studies for better insights on fibre surface treatments and resin systems interactions. In this work, Curaua fibres were treated using silane coupling agents to improve their interfacial properties with polyester. The fibres were pre-treated using 4?wt% solution of NaOH and then treated with 5?wt% solution of (3-aminopropyl) trimethoxysilane (AMPTS) or triethoxymethylsilane (TEMS). Characterisation of the treated fibres was carried out using infrared spectroscopy, X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. Fibre wettability and adhesion towards polyester was investigated using contact angle measurements and pull-out tests, respectively. The AMPTS treatment yielded a significant result of 20.2?MPa in interfacial shear strength (≈2.5 times that of the untreated fibre), attributed to the increase in availability of binding sites with polyester.     

Effect of silane‐coupling agents on interfacial properties of CF/PI composites

In this article, to form a structure‐controlled interface, carbon fiber (CF) surfaces were first activated by plasma technique and then hydroxylated by LiAlH₄ treatment, and then were reacted with a suit of silane‐coupling agents terminated with desired functional groups to form thin films, which further reacted with polyimide (PI) resin to generate a strong adhesion interface. The morphology, structure, and composition of CF surfaces before and after treatment were investigated by atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), and X‐ray photoelectron spectroscopy (XPS), respectively. The results of FTIR and XPS analysis showed that silane‐coupling agents were successfully chemisorbed onto the CF surfaces by the hydrolysis and condensation reactions. The interfacial shear strength of the CF/PI microcomposites was evaluated by the microbond technique. The results showed that the types of the interfacial functional groups, especially the vinyl end groups in vinyltriethoxysilane (VS), which can react with PI resin, had very significant influence on the improvement of the interfacial adhesion properties of composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Influence of silane coupling agents on the surface energetics of glass fibers and mechanical interfacial properties of glass fiber-reinforced composites

The effect of various silane coupling agents on glass fiber surfaces has been studied in terms of the surface energetics of fibers and the mechanical interfacial properties of composites. γ-Methacryloxypropyltrimethoxysilane (MPS), γ-aminopropyltriethoxysilane (APS), and γ-glycidoxypropyltrimethoxysilane (GPS) were used for the surface treatment of glass fibers. From contact angle measurements based on the wicking rate of a test liquid, it was observed that silane treatment of glass fiber led to an increase in the surface free energy, mainly due to the increase of its specific (or polar) component. Also, for the glass fiber-reinforced unsaturated polyester matrix system, a constant linear relationship was observed in both the interlaminar shear strength (ILSS) and the critical stress intensity factor (K_IC) with the specific component, γ_S ^SP, of the surface free energy. This shows that the hydrogen bonding, which is one of the specific components of the surface free energy, between the glass fibers and coupling agents plays an important role in improving the degree of adhesion at the interfaces of composites.     

Effect of fiber treatments on mechanical properties of coir or oil palm fiber reinforced polyester composites

The use of plant fibers as a reinforcement in polyester matrices requires the issue of compatibility between the two phases to be addressed. Because plant fibers present hydrophilic surfaces and polyesters are generally hydrophobic, poor fiber–matrix dispersion and wetting of the fibers by the matrix may result. As a consequence, the mechanical properties of the composite are severely reduced. This study considers the effect of fiber treatment by chemical modification of the fibers (acetylation) or the use of silane or titanate coupling agents on the mechanical properties of coir or oil palm reinforced polyester composites. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1685–1697, 2000     

Interfacial adhesion in polyester resin concrete

Silane coupling agents are widely used to improve the interfacial adhesion between the inorganic filler and the organic polymer matrix of polymer concretes. The mechanical properties of the concretes are also found to improve on the addition of silane coupling agents. This paper compares two methods of silane application; pretreatment of aggregates with silane and direct addition of silane to the resin, on the interfacial adhesion in polyester resin concrete for three different silanes. The effects of other parameters, such as the silane loading, predrying of aggregates before silane treatment, addition of CaCO₃ microfiller and pH of the silane treatment medium, are also investigated.     

Grafting acrylate functionalities at the surface of carbon fibers to improve adhesion strength in carbon fiber–acrylate composites cured by electron beam

Acrylate functionalities were grafted at the surface of carbon fibers in order to improve the adhesion strength with an acrylate matrix cured by electron beam. An isocyanate bearing aliphatic urethane acrylate was used as a coupling agent. As revealed by X-ray photoelectron spectroscopy, the isocyanate groups reacted with carboxylic acids and hydroxyl groups located at the surface of the fiber, leading to a covalent bonding of the acrylate groups. The adhesion strength was measured by a micromechanical test derived from the pull-out test. A significant improvement of the interfacial shear strength was obtained (+91%) with an electron beam curing. For comparison, an isothermal cure by UV was also investigated and led to the same level of adhesion strength. The improvement was also proved by an increase in the 90° flexural strength of unidirectional composites (+38%). Grafting functionalities that were compatible with the radical mechanism of the polymerization of the matrix appeared to be a promising strategy for the improvement of the mechanical properties of carbon fiber–acrylate composites cured by electron beam.     

The Effect of Nitric Acid Oxidization Treatment on the Interface of Carbon Fiber-Reinforced Thermoplastic Polystyrene Composite

The quality of interfacial interaction is dictated by the surface chemistry of the carbon fibers and the composition of the matrix. The composition of polystyrene was modified by the addition of maleic anhydride (MAH) grafted polystyrene. The surface properties of the various matrix formulations were characterised by contact angle. Carbon fibers were modified by oxidation in nitric acid. The surface composition of the carbon fibers was characterized. The interaction between modified polystyrene and the carbon fibers was studied by single fiber pull-out tests. The best adhesion behavior was achieved between polystyrene containing grafted MAH and nitric acid oxidation carbon fibers. The addition of MAH-grafted polystyrene to the unmodified polystyrene caused the interfacial shear strength to increase. The apparent interfacial shear strength of this fiber-matrix combination allowed for the utilisation of 100% of the yield tensile strength of polystyrene.     

High-performance poly(lactic acid)/starch materials prepared via starch surface modification and its in situ enhancement

High-performance modified poly(lactic acid) (PLA)/starch (ST) blends were prepared by incorporating silane coupling agent. The coupling agent acted as a bridge between PLA and ST components, enhancing their interfacial compatibility during the melt blending. The addition of epoxy-functionalized silane coupling agent improved the interfacial adhesion between PLA and ST phases, as evidenced by the decreased number and spacing of gaps between the ST particles and PLA matrix. The coupling agent also filled the surface crack of the ST particles, improving their dispersion in PLA matrix. The tensile strength of the modified PLA/ST blend increased from 19.6 MPa for the neat PLA/ST blend to 53.4 MPa, exceeding that of neat PLA. The modified blend also showed improved hydrophobicity and thermal stability. This research presented an effective approach to reducing the cost of PLA-based materials and improving the performance of ST-filled PLA materials by enhancing the interfacial adhesion between ST and PLA through surface modification with silane coupling agent. It provided a simple and feasible strategy for the high-performance modification of polyester/ST materials.     

Influence of Fiber Surface Modification on the Mechanical Performance of Isora-Polyester Composites

This paper reports the effect of chemical treatment on the mechanical properties of a natural fiber, isora, as reinforcement in unsaturated polyester resin. Isora fiber is separated from the bark of the Helicteres isora plant by a retting process. The short isora fiber surface was modified chemically by acetylation, benzoylation, silane and triton treatments to bring about improved interfacial interaction between the fiber and the polyester matrix. The modified surfaces were characterized by IR spectroscopy and SEM. The SEM studies were carried out to investigate the fiber surface morphology, fiber pull-out and fiber-polyester interface bonding. They showed the changes occuring on the fiber surface during chemical treatment. Properties like tensile strength, flexural strength and impact strength have been studied. The chemical modification of fiber improved fiber/matrix interaction as evidenced by the enhanced tensile and flexural properties. The lower impact properties of the composites, except triton-treated fiber composite, further point to the improved fiber/matrix adhesion, compared to the untreated fiber composites.     

Silane coupling agents in basalt-reinforced polyester composites

A new reinforcing mineral fibre, comparable in strength (3 MPa) and modulus (90 MPa) with E-glass fibres, has recently been produced from naturally-occurring basalt rock. Following earlier studies of basalt fibre/polymer matrix interactions by single fibre pull-out tests, the interfacial interaction in basalt/polyester composite systems has now been investigated. The effect of silane coupling agents applied under various conditions is reported here. The controlling effects of silane hydrolysis, condensation, orientation on the basalt surface and chemical bonding on the surface are revealed in corresponding variations in flexural strengths.     

低温等离子体对PBO纤维表面的改性

采用硅烷偶联剂处理聚对苯撑苯并双噁唑(PBO)纤维,利用常压射频低温等离子体对PBO纤维进行了表面处理,通过扫描电镜、红外光谱、光学显微镜等研究了处理时间对PBO纤维表面官能团和表面形貌的影响规律,通过单丝拔出实验测定PBO纤维基复合材料的界面剪切强度。结果表明:经过常压射频低温等离子体处理后,PBO纤维的表面形成了大量的极性基团,表面产生明显的凹坑,PBO纤维与树脂的粘接性能提高50%,纤维的拉伸强度下降5%。     

The influence of surface modifications of glass on glass fiber/polyester interphase properties

Unsized glass fibers and planar glass substrates were subjected to low temperature plasma or wet-chemical process to modify the fiber or substrate surface and thus influence the interphase properties of the glass/polyester system. Plasma-polymerized thin films (interlayers) of organosilicon monomers (hexamethyldisiloxane and vinyltriethoxysilane) were deposited in an RF helical coupling plasma system on the glass surface. Commercial silane coupling agent (vinyltriethoxysilane) was coated onto an unmodified glass surface from an aqueous solution. Bonding at the glass/interlayer interface was analyzed by employing a micro-scratch tester together with an optical polarizing microscope for the planar samples. The results revealed that the adhesion bonding could be controlled by plasma process parameters. Scanning electron and atomic force microscopies enabled characterization of the film surface morphology. Chemical composition and chemical structure of prepared interlayers were characterized using X-ray photoelectron and infrared spectroscopies. Microcomposites (macrocomposites) were tested to evaluate the interfacial shear strength (short-beam strength) of the glass fiber/polyester interphase using the microbond test (short-beam shear). Our study indicated that the most efficient interphase could be prepared by plasma polymerization or wet-chemical process using the vinyltriethoxysilane monomer. The short-beam strength was 110% higher than that for untreated fibers in both cases.     

Effect of surface treatment of ramie fiber on the interfacial adhesion of ramie/acetylated epoxidized soybean oil (AESO) green composite

Recently, many researchers have attempted to convert soybean oil into useful polymers. One of the ways to make soybean oil into a matrix of green composites is to modify its triglyceride structure to obtain the acrylated epoxidized soybean oil (AESO) through epoxidization and acrylation. In this study, the effects of ramie fiber surface treatments such as acetylation, silane, and peroxide treatments on the chemical, morphological, and interfacial adhesion properties of a ramie/AESO green composite were studied. Surface-treated fibers were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and dynamic contact angle analysis. The crystallinity and thermal stability of chemically treated fibers were investigated by wide angle X-ray diffraction and thermogravimetric analyzer. It was demonstrated that surface treatments lead to several morphological changes, including the formation of micro-cracks and removal of impurities by acetylation and peroxide treatment as well as surface smoothing by silane treatment. Surface energy of acetylated fiber decreased with treatment time and showed the lowest value for silane treated fiber. The interfacial shear strength (IFSS) of a fiber/AESO composite was investigated through the microbond test. The IFSS of silane treated ramie was higher than that of others. The result indicates that silane treated fibers improve the interfacial property, which is the most important characteristic for the end use of green composites.     

Polymerization of styrene-isoprene on glass cloth for use in composite manufacture

The evaluation of a new process for promoting the adhesion of thermosetting resins to a reinforcing fiber is described. In this process, termed admicellar polymerization, monomers are polymerized inside a surfactant bilayer adsorbed on a surface. Admicellar polymerization is essentially a surface analogue of emulsion polymerization. This technique can place a variety of polymers at the surface of the reinforcing agent, so that the interfacial layer can be tailored at will. In this study, a styrene-isoprene copolymer was polymerized on the surface of glass mats. Epoxy-matrix composites made with untreated cloth, silane-treated cloth, and admicellar-treated cloth were evaluated via three-point bend tests and single filament pull-out tests. The epoxy-matrix composites made from admicellar-treated and silane-treated cloth gave significantly higher strengths in three-point bend tests than composites made from untreated cloth. Single filament pull-out tests, which measure fiber-matrix adhesion directly, and scanning electron micrographs of the failure interface gave results consistent with three-point bend tests. This paper indicates that admicellar polymerization deserves further study as an alternative to silane coupling agents in structural composites.     

Role of silanes in adhesion. Part II. Dynamic mechanical properties of silane-treated glass fiber/polyester composites

—Glass fiber/unsaturated polyester composites, prepared by impregnating glass braid with varying thickness coatings (from 200 Å up to 1600 Å thick) of polyester resin, were tested with a DuPont Dynamic Mechanical Analyzer. The effects of the polyester resin thickness and silane treatments on the dynamic mechanical properties of the composites were evaluated. The results are supported by Fourier transform infrared spectroscopy of the composite materials. It is shown that both the concentration and the organo-functional group of the silane coupling agent influence the damping, storage, and loss moduli as well as the glass transition temperature (T_g) of the matrix resin in the closest vicinity to the glass/resin bondline. In the absence of a silane inner layer, a low T_g, 'soft' boundary layer exists due to inhibition of the polyester resin cure by the glass surface. It is noted that a reactive silane, such as γ-methacryloxypropyltrimethoxysilane, promotes the formation of a 'soft' or 'rigid' (high T_g) boundary layer, depending on the concentration of the silane in the treating solution. On the other hand, a non-reactive silane, such as methyltrimethoxysilane, produces a 'rigid' interphase in the entire range of concentrations of the silane solution. An attempt was made to correlate the dynamic mechanical properties of the boundary layer with the fiber/polymer interfacial shear strength. Upon pretreatment of glass fibers with silane coupling agents, the relative magnitude of the loss modulus, E", and the nature of the boundary layer (T_g) seem to be better indicators of efficient stress transfer from the polymer to the glass fiber in the composite system than tan δ. Efficient stress transfer is characterized by a low value of E" and 'soft' boundary layers. The results suggest that the mere presence of glass/polyester chemical bonding is insufficient to ensure effective stress transfer. A strong bond results from the synergistic effect of glass/silane/polymer chemical bonding and a 'soft' boundary layer.     

Synthesis and characterization of a rigid-rod dihydroxy poly(<Emphasis Type="Italic">p</Emphasis>-phenylene benzobisoxazole) fiber with excellent surface and axial compression properties

A series of dihydroxy poly(p-phenylene benzobisoxazole) (DHPBO) were prepared by introducing binary hydroxyl polar groups into poly(p-phenylene benzoxazole) PBO macromolecular chains and the effects of hydroxyl polar groups on surface wettability, interfacial adhesion and axial compression property of PBO fiber were investigated. Contact angle measurement showed that the wetting process both for water and for ethanol on DHPBO fibers were obviously shorter than that on PBO fibers, implying DHPBO fibers have a higher surface free energy. Meanwhile, single fiber pull-out test showed that DHPBO fibers had higher interfacial shear strength than that of PBO fibers. Scanning electron microscope proved that there was more resin remained on the surface of DHPBO fibers than on PBO fibers after pull-out test. Furthermore, axial compression bending test showed that the introduction of binary hydroxyl groups into macromolecular chains apparently improved the equivalent bending modulus of DHPBO fibers.     

Grafting starch nanocrystals onto the surface of sisal fibers and consequent improvement of interfacial adhesion in sisal reinforced starch composite

Starch nanocrystals (SNCs) were obtained by the hydrolysis of waxy starch and used to improve the interfacial adhesion of a composite of sisal fibers and starch. Sisal fibers were first treated with acrylic acid (AA), and the modified fibers were then reacted with SNCs to form ester groups. The grafted fibers were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The FTIR and XPS results showed that the SNCs were successfully grafted onto the surface of SF-AA, and an ester linkage was formed during the reaction of AA with the SNCs. The SEM analysis showed that the SNCs were distributed over the fiber surface. Tensile tests and pull-out tests were also performed utilizing a two-parameter Weibull distribution analysis to study the effect of the grafted SNCs on the mechanical and interfacial properties. Compared to the untreated fibers, the interfacial shear strength of the grafted SNCs fibers increased by 79.3%. Therefore, the structural similarity between starch and the SNCs contributed towards their compatibility and improved interfacial properties, with the introduction of SNCs being used as an alternative material for fiber surface modification. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47202.     

Effects of polyamide 6 incorporation to the short glass fiber reinforced ABS composites: an interfacial approach

The properties of 30 wt% short glass fiber (SGF) reinforced acrylonitrile-butadiene-styrene (ABS) terpolymer and polyamide 6 (PA6) blends prepared with extrusion were studied using the interfacial adhesion approach. Work of adhesion and interlaminar shear strength values were calculated respectively from experimentally determined interfacial tensions and short beam flexural tests. The adhesion capacities of glass fibers with different surface treatments of organosilanes were evaluated. Among the different silanes tested, γ-aminopropyltrimethoxysilane (APS) was found to be the best coupling agent for the glass fibers, possibly, because of its chemical compatibility with PA6. Tensile test results indicated that increasing amount of PA6 in the polymer matrix improved the strength and stiffness of the composites due to a strong acid–base interaction at the interface. Incorporation of PA6 to the SGF reinforced ABS reduced the melt viscosity, broadened the fiber length distributions and increased the toughness of the composites. Fractographic analysis showed that the incorporation of PA6 enhanced the interactions between glass fibers and the polymeric matrix.     

硅烷偶联剂改性芳纶工艺研究

采用KH550硅烷偶联剂处理芳纶,将处理温度、时间、硅烷偶联剂的质量分数作为3个因素进行分析,通过单因素分析法确定每个因素对处理前后芳纶与树脂的界面剪切强度的影响,结合扫描电镜观察处理前后纤维的表面结构变化,得到最佳处理的工艺为:处理时间9 h、温度45℃、硅烷偶联剂的质量分数为25%。