Atomistic Investigation on the Effects of Thermal Loading on Interfacial Adhesion of Dissimilar Materials

Heat transfer has a large effect on the adhesion and the corresponding failure at material interfaces. When a system becomes extremely small, the conventional finite element method is not capable of accurately capturing all the information, and precise modeling of interfacial properties is essential. In this paper, molecular dynamics (MD) simulations are used to investigate the effects of heat transfer on the adhesion properties of material interfaces. For Al–W and Cr–W interfaces, the interfacial strengths are calculated by MD simulations and are compared with the critical loads obtained from scratch tests. Both the results of MD simulations and experiments show that the interfacial strength of an Al–W interface is larger than that for a Cr–W interface; and furthermore, the Cr–W interface is more sensitive to thermal loading than the Al–W interface. In this work we concluded that the proposed MD model can be used to estimate interfacial adhesion under the effects of heat transfer.     

Surface modification of cellulose fibers. II. The effect of cellulose fiber treatment on the performance of cellulose–polyester composites

Cellulose fibers treated with different coupling agents based on trichloro-s-triazine have been evaluated in terms of their reinforcement effect on unsaturated polyesters. The treatment with coupling agents containing double bonds resulted in what we believe to be the formation of covalent bonds between fiber and matrix. This has been compared with a treatment, which can only lead to formation of close interfacial molecular contact by wetting. The tensile properties of composites prepared from treated and untreated fibers were studied before and after exposure to water. It was found that all types of fiber treatment decreased water absorption and the reduction of mechanical properties in wet conditions, but that the degradation at the fiber/matrix interface which occurs from immersion in water and drying could only be avoided through the development of covalent bonds between fiber and matrix. Scanning electron microscopy was used to study the adhesion between fiber and matrix. An explanation of the reduction of mechanical properties of cellulose-fiber reinforced polymers in wet conditions is proposed.     

Influence of surface treatment of carbon fibers on interfacial adhesion strength and mechanical properties of PLA‐based composites

In the present study C/PLA composites with different fiber surface conditions (untreated and with nitric acid oxidation for 4 h and 8 h) were prepared to determine the influence of surface treatment on the interfacial adhesion strength and mechanical properties of the composites. A chemical reaction at the fiber–matrix interfaces was confirmed by XPS studies. Nitric acid treatment was found to improve the amount of oxygen‐containing functional groups (particularly the carboxylic group, —COOH) on carbon fiber surfaces and to increase the surface roughness because of the formation of longitudinal crevices. The treated composites exhibited stronger interface adhesion and better mechanical properties in comparison to their untreated counterparts. There was a greater percentage of improvement in interfacial adhesion strength than in the mechanical properties. The strengthened interfaces and improved mechanical performance have been mainly attributed to the greater extent of the chemical reaction between the PLA matrix and the carbon fibers. The increased surface roughness also has had a slight contribution. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 367–376, 2001     

Effect of coupling agents on rice‐husk‐filled HDPE extruded profiles

Lignocellulosic composites are diversifying their applications into various fields as they can meet the requirements of the respective applications by changing the matrix, fiber resource and processing ingredients. In this research work we explored the potential of extruded rice‐husk‐filled high density polyethylene (HDPE) composite profiles for structural applications. The structure and the properties of the interface in fiber‐reinforced composites play a crucial role in determining the performance properties of the composites. An optimum degree of adhesion between the fiber and the matrix is required for efficient stress transfer from the matrix to the fiber. Generally, coupling agents are used to improve the adhesion between lignocellulosic filler and the polymer matrix in structural composite materials. In this study, four different coupling agents based on ethylene‐(acrylic ester)‐(maleic anhydride) terpolymers and ethylene‐(acrylic ester)‐(glycidyl methacrylate) terpolymers were used to enhance the performance properties of the composites. The results indicated that these coupling agents enhanced the tensile and flexural strength of the composites significantly, and the extent of the coupling effect depends on the nature of the interface formed. Incorporation of coupling agents enhanced the resistance to thermal deformation and the water absorption properties of the composite, whereas it reduced the extrusion rate significantly. Among the four coupling agents used, EGMA1—the one with a glycidyl methacrylate functional group and without any methyl acrylate pendant group on the polymer backbone—was found to be the best coupling agent for the rice‐husk‐filled HDPE composites. Copyright © 2004 Society of Chemical Industry     

Mullite‐glass and mullite‐mullite interfaces: Analysis by molecular dynamics (MD) simulation and high‐resolution TEM

The properties of mullite‐glass and mullite‐mullite interfaces have been investigated at 1800 K by molecular dynamics (MD) simulation and high‐resolution TEM. The simulation showed that mullite‐glass interfaces typically have much lower interfacial energies than mullite‐mullite interfaces, which results from the structural flexibility of the glass and associated accommodation of interfacial mismatch. The (110)‐glass interface has the lowest energy of all interfaces studied, which is consistent with the observed dominance of this interface in experimental mullite‐glass samples examined by TEM. The simulation shows that the interfacial energies of the (100)‐glass and (010)‐glass interfaces are higher than that those of the (001)‐glass interface, so [100] and [010] would be expected to be the dominant growth directions. However, the growth of mullite in glass occurs predominantly in the [001] direction. This apparent discrepancy can be explained by the fact that growth in the [100] and [010] directions is limited by the slow growth of (110) plane (i.e., [110] direction), which facilitates [001] growth, which is confirmed by the TEM data.     

界面改性方法对玻纤增强聚丙烯复合材料力学性能的影响

在对玻璃纤维的偶联剂处理,基体接枝改性的基础上,考察不同界面改性方法对玻纤增强聚丙烯力学性能的影响,并通过扫描电镜对玻纤增强聚丙烯的界面进行研究。结果表明,经偶联剂表面处理的玻纤与未经接枝改性的聚丙烯不能形成有效的界面粘结,力学性能较差,而与接枝改性的聚丙烯界面粘结较好,力学性能也有较大幅度的提高;经偶联剂处理的玻纤能与改性聚丙烯形成良好的界面粘结,改善复合材料的力学性能,偶联剂种类的变化在一定程度上能够改善复合材料的性能。     

Development of lightweight thermoplastic composites based on polycarbonate/acrylonitrile–butadiene–styrene copolymer alloys and recycled carbon fiber: Preparation,morphology, and properties

Thermoplastic composites of polycarbonate (PC)/acrylonitrile–butadiene–styrene copolymer (ABS) alloys reinforced with recycled carbon fiber (RCF) were prepared by melt extrusion through a twin‐screw extruder. The RCF was first cleaned and activated with a concentrated solution of nitric acid and was then surface‐coated with diglycidyl ether of bisphenol A as a macromolecular coupling agent. Such an approach is effective to improve the interfacial bonding between the fibers and the PC/ABS matrix. As was expected, the reinforcing potential of the RCF was enhanced substantially, and furthermore, the mechanical properties, heat distortion temperature, and thermal stability of PC/ABS alloys were significantly improved by incorporating this surface‐treated RCF. The composites also obtained a reduction in electrical resistivity. The morphologies of impact fracture surfaces demonstrated that the RCF achieved a homogeneous dispersion in the PC/ABS matrix due to good interfacial adhesion between the fibers and the matrix. In addition, the introduction of RCF into PC/ABS alloys also resulted in an increase in the storage moduli of the composites but a decrease in the loss factors. It is prospective that, with such good performance in mechanical data, heat resistance, and electrostatic discharge, the RCF‐reinforced PC/ABS composites exhibit a potential application in industrial and civil fields as high‐performance and lightweight materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The reinforcement mechanism of fiber-glass reinforced plastics under wet conditions: A review

Reinforcement mechanisms of fiber-glass reinforced plastics (FRP) under wet conditions are reviewed with emphasis on molecular structures of glass/matrix interfaces. Included are studies on glass surface, the glass/coupling agent interface, silane coupling agents on glass surfaces as well as in solution, the coupling agent/matrix interface, extending to the interphase of particulate-filled composites, and matrix resin. For a better understanding of wet strength of FRP, the structures under dry conditions are extensively, reviewed. The chemical bonding theory still dominates other reinforcement theories. The importance of other factors such as orientation of silane coupling agents and the restriction of matrix polymer conformations are also considered. Based on recent development in spectroscopy, molecular level research of the glass/matrix interfaces has been initiated in the past decade, yet only a few spectroscopic investigations on the function of water have appeared. It is concluded that the correlation between spectroscopic investigations and mechanical properties of a FRP is indispensable.     

GF/PP复合材料悬浮法工艺中偶联剂的应用及其对材料性能的影响

研究了悬浮法制备短玻璃纤维增强聚丙烯复合材料过程中不同偶联剂的适用性及其对材料性能的影响。根据悬浮法工艺的特点 ,提出了适用的偶联剂品种和添加方式。探讨了悬浮体系中偶联剂对复合材料微观结构的影响和偶联作用机理     

Influence of grafted polypropylene on the mechanical properties of mineral‐filled polypropylene composites

The purpose of this work was to study how mineral fillers would behave in a polypropylene (PP) matrix when PP modified with maleic anhydride (MA) and/or itaconic acid (IA) was used as a coupling agent in the preparation of mineral‐filled PP composites. The composites were characterized with tensile mechanical measurements and morphological analysis. The optimum amount of the coupling agent to be used to obtain composites with improved mechanical properties was established. The results indicated that these coupling agents enhanced the tensile strength of the composites significantly, and the extent of the coupling effect depended on the nature of the interface that formed. The incorporation of coupling agents enhanced the resistance to deformation of the composite. The behavior of IA‐modified PP as a coupling agent was similar to that of a commercial MA‐modified PP for the filled PP composites. Evidence of improved interfacial bonding was revealed by scanning electron microscopy studies, which examined the surfaces of fractured tensile test specimens; their microstructures confirmed the mechanical results with respect to the observed homogeneous or optimized dispersion of the mineral‐filler phase in these composites. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2343–2350, 2007     

Role of N-(β-amino ethyl) γ-aminopropyl trimethoxy silane as Coupling Agent on the Jute-polycarbonate Composites

New composites of jute fabrics and polycarbonate (PC) were prepared by compression molding. The surface of the composites was modified by coupling agents N-(β-amino ethyl) γ-aminopropyl trimethoxy silane (Z-6020) to improve the interfacial adhesion between jute and PC. Enhanced mechanical properties were produced by the modified jute composites. The treated and untreated jute surface as well as composites were characterized by Fourier-transform infrared spectroscopy (FTIR), environmental scanning electron microscopy (ESEM), and differential scanning calorimetry (DSC).     

Parameters regulating interfacial and mechanical properties of short glass fiber reinforced polypropylene

The performance of thermoplastic composites is known to depend on the intrinsic properties of the two composite components, the quality of the fiber–matrix interface, and the crystalline properties of their matrix. The objective of this work is to characterize the effect of the addition of modified polypropylene (PP) and silane coupling agent on the mechanical and interfacial properties of short fiber reinforced PP composites. Differential scanning calorimetry (DSC), single fiber composite fragmentation tests (SFC), and mechanical testing are used to understand the different parameters regulating the interfacial properties of composites. No influence of the modified PP on the level of crystallinity is observed. Some differences in the size of the spherulites are observed for acrylic acid grafted PP (PP‐g‐AA). Those samples also show lower mechanical properties in spite of good interfacial interactions. Maleic anhydride grafted PP (PP‐g‐MAh) leads to better mechanical performances than PP‐g‐AA. A high MAh content PP‐g‐MAh grade with low viscosity is the best polymeric additive used in the present work. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2047–2060, 2000     

Effects of interfacial adhesion on properties of polypropylene/Wollastonite composites

Wollastonite reinforced polypropylene (PP/CaSiO₃) composites were prepared by melt extrusion. A silane coupling agent and a maleic anhydride grafted PP (PP‐g‐MA) were used to increase the interfacial adhesion between the filler and the matrix. The increased adhesion observed by scanning electron microscopy (SEM) resulted in improved mechanical properties. A model was applied to describe the relationship between the interfacial adhesion and tensile properties of PP/CaSiO₃ composites. There is stronger interfacial adhesion between silane‐treated CaSiO₃ and polymer matrix containing PP‐g‐MA as a modifier. Results of dynamic mechanical thermal analysis (DMTA) showed that stronger interfacial adhesion led to higher storage modulus. The influence of CaSiO₃ particles on the crystallization of PP was studied by using differential scanning calorimetry (DSC). The introduction of CaSiO₃ particles does not affect the crystallization temperature and crystallinity of PP matrix significantly. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Wood‐fiber/high‐density‐polyethylene composites: Coupling agent performance

The coupling efficiency of seven coupling agents in wood–polymer composites (WPC) was investigated in this study. The improvement on the interfacial bonding strength, flexural modulus, and other mechanical properties of the resultant wood fiber/high‐density polyethylene (HDPE) composites was mainly related to the coupling agent type, function groups, molecular weight, concentration, and chain structure. As a coupling agent, maleated polyethylene (MAPE) had a better performance in WPC than oxidized polyethylene (OPE) and pure polyethylene (PPE) because of its stronger interfacial bonding. A combination of the acid number, molecular weight, and concentration of coupling agents had a significant effect on the interfacial bonding in WPC. The coupling agents with a high molecular weight, moderate acid number, and low concentration level were preferred to improve interfacial adhesion in WPC. The backbone structure of coupling agents also affected the interfacial bonding strength. Compared with the untreated composites, modified composites improved the interfacial bonding strength by 140% on maximum and the flexural storage modulus by 29%. According to the statistical analysis, 226D and 100D were the best of the seven coupling agents. The coupling agent performance was illustrated with the brush, switch, and amorphous structures. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 93–102, 2005     

Microstructure and fracture behavior of polypropylene/barium sulfate composites

The microstructure, mechanical properties, and fracture behavior of polypropylene (PP)/barium sulfate (BaSO₄) composites were studied. Four composite samples with different PP‐BaSO₄ interface were prepared by treating the filler with different modifiers. The fracture behavior of the composites under different strain rates was studied by means of Charpy impact tests and essential work of fracture (EWF) tests. It is shown that a moderate interfacial adhesion is favorable for toughening, which ensures that the particles transfer the stress and stabilizes the cracks at the primary stage of the deformation, and satisfies the stress conditions of plastic deformation for matrix ligaments subsequently via debonding. Very strong interfacial adhesion is not favorable for toughness, especially under high strain rate, because the debonding‐cavitation process may be delayed and the plastic deformation of matrix may be restrained. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1207–1213, 2006     

玉米秸秆增强废胶粉复合材料的制备及界面改性

采用共混法制备了玉米秸秆/废胶粉复合材料,并以4种不同偶联剂（硅烷偶联剂KH 550、KH 590、Si 69和钛酸酯偶联剂HY 101）分别对复合材料进行界面改性,探讨了玉米秸秆的增强及偶联剂改性对复合材料力学性能、界面形貌和组成结构及热稳定性的影响。结果表明,玉米秸秆的加入可有效提高复合材料的力学性能。偶联剂改性处理明显改善了玉米秸秆与废胶粉基质间的界面结合,进一步提高了复合材料的力学性能、热稳定性和相容性。综合来看,当玉米秸秆用量为25份（质量）时,在四种偶联剂用量均为玉米秸秆质量分数6%的条件下,采用Si 69的改性效果最佳,KH 590次之,HY 101和KH 550的改性效果则较为一般。     

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     

Use of silanes and copolymers as adhesion promoters in glass fiber/polyethylene composites

Two organofunctional silanes and three functionalized copolymers were used as adhesion promoters in glass fiber/polyethylene‐reinforced composites. The performance of the coupling agents was investigated by mechanical property measurements, scanning electron microscopy, and dynamic mechanical analysis. Coupling achieved with the poly(ethylene‐g‐maleic anhydride) copolymer proved to be the most successful compared with the other copolymers (ethylene/vinyl alcohol, ethylene/acrylic acid) and silane agents (γ‐methacryloxypropyltrimethoxy, cationic styryl). The combined coupling performance of the silanes and copolymers examined in this study appears to be controlled by the coupling performance of the copolymer. Effective coupling was reflected in increased mechanical properties. Increased fiber/matrix adhesion is not always associated with effective coupling because structural changes occurring at the interface region can result in a deterioration of the material property. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2877–2888, 2001     

Effect of Adhesive Thickness on Joint Strength: A Molecular Dynamics Perspective

Recent studies suggest that adhesion in thin joints depends on several factors including temperature, interface toughness, strain rate, surface roughness of adherends, bondline thickness of adhesives, and many others. Influence of thickness on joint properties is surprising but experimentally well documented without reasonable explanations. In this study, we attempt to address the mechanical behavior of polymer adhesives by molecular dynamics (MD) simulation. We show that interfacial strength of the joints in tensile, shear, or combined loading significantly depends on the coupling strength between adhesives and adherends. Failure of joints is always at the interface when coupling strength is weaker. With stronger interfaces, cohesive failure occurs by cavitation or by bulk shear depending on the loading condition. When joints are loaded in tension, it requires an exceedingly stronger interface to realize pure shear failure, otherwise failure is through interface slip. Under a mixed mode condition, interface slip is difficult to avoid. As long as failure is not at the interface alone, the yield strength of joints improves significantly with the reduction of thickness. Increase in bulk density and change in polymer configurations with the reduction of adhesive thickness are believed to be the two key factors in improving mechanical behavior of adhesives.     

On adhesion mechanisms and interfacial strength in acrylonitrile–butadiene–styrene/wood sawdust composites

Adhesion mechanisms and interfacial strengths of acrylonitrile–butadiene–styrene (ABS) copolymer/wood sawdust composites containing two different silane coupling agents [3-Methacryloxypropyl trimethoxysilane (KBM503) and N-2(aminoethyl)3-aminopropyl trimethoxysilane (KBM603)] were studied using the Fourier Transform Infrared (FTIR) technique and mechanical testing. The results suggested that increasing wood sawdust content tended to increase the modulus of the composites, but decreased the strength of the composites. Concentrations of 1.0 wt% KBM503 and 0.5 wt% KBM603 were recommended for the optimization of the mechanical properties of the composites, respectively. Up to the recommended dosages, KBM603 was more effective in terms of the improved interfacial strength of the composites. The adhesion mechanism performed by KBM503 involved dipole–dipole interaction at the ABS/sawdust interface, whereas that by KBM603 was associated with covalent chemical bonds at the interface. The improved interfacial strength of the composites was reduced by the increased amounts of wood sawdust particles.