Fiber-Matrix Interfacial Adhesion Improvement in Carbon Fiber-Bisphenol-A Polycarbonate Composites by Polymer Grafting

Fiber-matrix interfacial adhesion in thermoplastic composites is generally poor due to the lack of formation of strong covalent and/or ionic bonds between the generally inert thermoplastic resins and the surface of the reinforcing fiber. Adhesion can be improved by forming covalent linkages between the fiber and the matrix by grafting a polymer of appropriate compatibility, molecular weight, and sufficient density onto the surface of the fiber. We have grafted low molecular weight polycarbonate and polymethyl methacrylates onto the surface of carbon fibers and measured an improvement in the level of adhesion ranging from 25% to100% over the ungrafted composites. It was also observed that the level of improvement in adhesion appears to be independent of the molecular weight of the grafted polymer. Examination of the fracture surface of these composites reveals that the failure is cohesive in the matrix for the polymer grafted fiber composites, while it is adhesive for the ungrafted composites.     

Production of leather-like composites using short leather fibers. II. Mechanical characterization

Leather-like composites were prepared by addition of chemically modified short leather fibers (SLF) into a plasticized polyvinyl chloride (pPVC) matrix. The fibers were subjected to chemical modification by emulsion polymerization to achieve good interfacial adhesion between SLF and the pPVC matrix. The SLF with chemical modification were obtained from three different reaction conditions where these SLF have different percentages of grafted and deposited PMMA polymer onto the fiber surface. The incorporation of the SLF into the thermoplastic matrix was carried out using a torque-rheometer and the composites obtained were molded by compression. Tensile and tear mechanical tests were performed on composite samples, and the morphology of the fractured surfaces was analyzed using scanning electron microscopy (SEM). The results show that the incorporation by grafting of polymethyl metacrylate (PMMA) onto the fibers produced a significant improvement of their interfacial adhesion to pPVC, promoting the compatibilization between the fiber surface and matrix. The findings are discussed and interpreted in terms of enhanced adhesion at phase boundaries. Overall, the results confirm that it is possible to produce modified leather composites based on a pPVC matrix, which exhibit relatively high tensile strength, tear resistance and flexibility. These composites are very suitable candidate materials for applications in the footwear industry.     

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).     

Catalytic grafting: A new technique for polymer/fiber composites. II. Plasma treated UHMPE fibers/polyethylene composites

In this paper, the catalytic grafting technique for preparation of polymer/fiber composites is extended to plasma treated ultra-high modulus polyethylene (UHMPE) fiber/high density polyethylene (HDPE) system. The OH groups introduced on the UHMPE fiber surface by oxygen plasma treatment were used to chemically anchor Ziegler-Natta catalyst which then was followed by ethylene polymerization on the fiber surface. The morphology and interfacial behavior, as well as the mechanical properties, of the HDPE composites reinforced by catalytic grafted or ungrafted UHMPE fibers were investigated by SEM, DSC, polarized light optical microscopy, and tensile testing. The experimental results show that the polyethylene grafted on the fibers acted as a transition layer between the reinforcing UHMPE fibers and a commercial HDPE matrix. The interfacial adhesion was also significantly improved. Compared with the composite reinforced by ungrafted UHMPE fibers, the composite reinforced by catalytic grafted UHMPE fibers exhibits much better mechanical properties.     

ESCA spectroscopy of poly(methyl methacrylate) grafted onto wood fibers

The incompatibility of hydrophilic wood fiber and hydrophobic polymers is the main difficulty with wood thermoplastic polymer composites. To overcome this issue, many researchers suggest grafting polymer onto wood fiber for improving the interfacial adhesion during mixing. A systematic ESCA study of chemi-thermo-mechanical pulp (CTMP) grafted fiber has been performed to provide chemical information about surface composition modification. The material analyzed included initial CTMP fiber, the pure polymer i.e., poly(methyl methacrylate) (PMMA) as reference material, and grafted fiber at different polymer loadings. Interest is focused on the carbon and oxygen spectra. Samples at high polymer loading or high grafting level have an O/C, C₁, C₂, C₄, O₁, and O₂ intensities much similar to those of the PMMA but a little different since some wood fiber sites have still not fixed the polymer. ESCA spectra provide information on about 1–5 nm depth. The ESCA technique allows the monitoring of grafting polymer onto wood fiber as a surface phenomenon.     

Enzyme‐mediated surface modification of jute and its influence on the properties of jute/epoxy composites

Surface modification of jute fibers is necessary to improve the adhesion and interfacial compatibility between fibers and resin matrix before using fibers in polymer composites. In this study, dodecyl gallate (DG) was enzymatically grafted onto the jute fiber by laccase to endow the fiber with hydrophobicity. A hand lay‐up technique was then adopted to prepare jute/epoxy composites. Contact angle and wetting time measurements showed that the surface hydrophobicity of the jute fabric was increased after the enzymatic graft modification. The water absorption and thickness swelling of the DG‐grafted jute fabric/epoxy composite were lower than those of the other composites. The tensile and dynamic mechanical properties of the jute/epoxy composites were enhanced by the surface modification. Scanning electron microscopy images revealed stronger fiber–matrix adhesion in composites with modified fibers. Therefore, the enzymatic graft modification increased the fiber–matrix interface area. The fiber–matrix adhesion was enhanced, and the mechanical properties of the composites were improved. POLYM. COMPOS., 38:1327–1334, 2017. © 2015 Society of Plastics Engineers     

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.     

Novel eco‐friendly biodegradable coir‐polyester amide biocomposites: Fabrication and properties evaluation

Biocomposites are prepared from a cheap, renewable natural fiber, coir (coconut fiber) as reinforcement with a biodegradable polyester amide (BAK 1095) matrix. In order to have better fiber‐matrix interaction the fibers are surface modified through alkali treatment, cyanoethylation, bleaching and vinyl grafting. The effects of different fiber surface treatments and fiber amounts on the performance of resulting bio‐composites are investigated. Among all modifications, cyanoethylated coir‐BAK composites show better tensile strength (35.50 MPa) whereas 7% methyl methacrylate grafted coir‐BAK composites show significant improvement in flexural strength (87.36 MPa). The remarkable achievement of the present investigation is that a low strength coir fiber, through optimal surface modifications, on reinforcement with BAK show an encouraging level of mechanical properties. Moreover, the elongation at break of BAK polymer is considerably reduced by the incorporation of coir fibers from nearly 400% (percent elongation of pure BAK) to 16‐24% (coir‐BAK biocomposites). SEM investigations show that surface modifications improve the fiber‐matrix adhesion. From biodegradation studies we find that after 52 days of soil burial, alkali treated and bleached coir‐BAK composites show significant weight loss. More than 70% decrease in flexural strength is observed for alkali treated coir‐BAK composites after 35 days of soil burial. The loss of weight and the decrease of flexural strength of degraded composites are more or less directly related.     

Promising approach to functionalisation of ground tyre rubber -photochemically induced grafting: Short Communication

Abstract

Ground tyre rubber (GTR) powder has been treated using a novel surface grafting process allowing the incorporation of various chemical functional groups onto the polymer surface. The GTR was functionalised with methacrylic acid by photoinitiated polymerisation. The process comprises two steps: UV irradiation of GTR in the presence of air, followed by grafting of methacrylic acid (MA) onto the GTR surface. The presence of reactive carboxy groups, which was confirmed by titration, provides the possibility of covalent linkage with reactive groups when the powder is blended with a suitable matrix polymer.

The effectiveness of the process was assessed by examining the tensile and Charpy impact properties of polyamide and epoxy compounds containing ungrafted and grafted GTR. A significant improvement in the tensile properties of polyamide was observed on adding methacrylic acid grafted GTR. The grafted GTR also worked as an impact modifier in epoxy compounds. The best results to date were achieved when methacrylic acid grafted GTR was added to polyurethane formulations.     

Copolymerization of polypropylene and functionalized linear α‐olefin onto glass fibers

This work deals with a novel glass fiber surface modification and subsequent metallocenic propylene polymerization onto it. Experimental results are presented on methylaluminoxane (MAO) fixation at the fiber surface, followed by propylene–α‐olefin graft copolymerization catalyzed by EtInd₂ZrCl₂/MAO. First results indicate that part of the produced polymer is chemically bonded to the glass fiber. Scanning electron microscopy, Fourier transform infrared spectroscopy, and X‐ray disperse energy microanalysis characterization confirm the permanence of a thin polymer layer as well as aluminum and oxygen (from the MAO) on the glass surface, even after a severe solvent extraction treatment. From these results, the copolymerization of hydroxy‐α‐olefin, grafted on MAO pretreated glass fiber, is foreseen as a possible way to improve fiber–matrix adhesion in glass fiber thermoplastic composites. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1266–1276, 2001     

The influence of fiber surface modification on the mechanical properties of coir‐polyester composites

Coir, an important lignocellulosic fiber, can be incorporated in polymers like unsaturated polyester in different ways for achieving desired properties and texture. But its high level of moisture absorption, poor wettability and insufficient adhesion between untreated fiber and the polymer matrix lead to debonding with age. In order to improve the above qualities, adequate surface modification is required. In our present work, fiber surface modification was effected through dewaxing, alkali (5%) treatment, aqueous graft copolymerization of methyl methacrylate (MMA) onto 5% alkali treated coir for different extents using CuSO₄ – NaIO₄ combination as an initiator system and cyanoexhylation with a view to improve the mechanical performance of coir‐polyester composites. Mechanical properties like tensile strength (PS), flexural strength (ES) and impact strength (IS) of the composites as a function of fiber loading and fiber surface modification have been evaluated. Composites containing z5 wt% of fiber (untreated) improved tensile and flexural strength by 30% and 27% respectively in comparison to neat polyester. The work of fracture (impact strength) of the composite with 25 wt% fiber content was found to be 967 J/m. The elongation at break of the composites exhibits an increase with the introduction of fiber, All types of surface modification result In improved mechanical properties of the composites. Significant improvement in mechanical strength was also observed for composites prepared from 5% PMMA grafted fiber.     

RFL coated aramid short fiber reinforced thermoplastic elastomer: Mechanical, rheological and morphological characteristics

Composite based on a new generation metallocene catalyzed thermoplastic elastomer ethylene-octene copolymer (EOC) and resorcinol formaldehyde latex (RFL) coated aramid short fiber was prepared by varying the short fiber loading from 1 to 10 phr. The mechanical, morphological and rheological characterizations were carried out. The impact of a low molecular weight maleic anhydride grafted 1, 2 polybutadiene (MA-g-PB) on various properties was also investigated. It has been observed that with increasing the short fiber content both the low strain modulus and modulus at 100% increase but the tensile strength and elongation at break decrease. The improvements in tensile strength coupled with elongation at break and good fiber dispersion particularly at high fiber loaded composite were achieved with the incorporation of MA-g-PB, which indicates that it acts as an interface modifier through compatibilization between the fiber and the EOC matrix as well as a good dispersing agent. The understanding of adhesion between the fiber and the polymer and the sticking of polymer traces on the tensile fractured fiber surface of the composite by scanning electron microscopic analyses further support the compatibilizing action of MA-g-PB. The melt rheological behavior such as storage modulus, loss modulus, complex viscosity and storage viscosity of the composites were investigated using a Rubber Process Analyser (RPA) under strain and frequency sweep mode.     

Improvement of interfacial adhesion of poly(m‐phenylene isophthalamide) short fiber–thermoplastic elastomer (SEBS) composites by N‐alkylation on fiber surface

A composite of short‐fiber, poly(m‐phenylene isophthalamide), and thermoplastic elastomer styrene (ethylene–butylene) styrene (SEBS), was investigated. The fiber surface was modified by N‐alkylation (heptylation and dodecylation) to improve their compatibility with a less polar SEBS matrix. Observation of fiber‐surface morphology by SEM revealed surface roughness after N‐alkylation. Nearly complete coating of the polymer matrix on the fiber was observed on a fractured surface of the composite, which is evidence for the improvement of fiber–matrix adhesion. It was found that the modulus of the composites grew with increasing fiber loading to approximately the same extent for both unmodified and modified fiber composites. Tensile strength of the modified fiber composites was found to improve significantly over that of the unmodified fiber composite. This suggests that the presence of the alkyl group on the fiber surface is responsible for an improvement of interfacial adhesion. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2414–2422, 1999     

Enhancement of PVC/ENR blend properties by poly(methyl acrylate) grafted oil palm empty fruit bunch fiber

Effect of oil palm empty fruit bunch (OPEFB) fiber and poly(methyl acrylate) grafted OPEFB on several mechanical properties of poly(vinyl chloride)/epoxidized natural rubber (PVC/ENR) blends were studied. The composites were prepared by mixing the fiber and the PVC/ENR blends using HAKEE Rheomixer at the rotor speed of 50 rpm, mixing temperature 150°C, and mixing period of 20 min. The fiber loadings were varied from 0 to 30% and the effect of fiber content in the composites on their ultimate tensile strength (UTS), Young's modulus, elongation at break, flexural modulus, hardness, and impact strength were determined. An increasing trend was observed in the Young's modulus, flexural modulus, and hardness with the addition of grafted and ungrafted fiber to the PVC/ENR blends. However the impact strength, UTS, and elongation at break of the composites were found to decrease with the increase in fiber loading. An increase in elongation at break and UTS and decrease in the flexural and Young's modulus was observed with the addition of PMA‐g‐OPEFB fiber compared to ungrafted fiber. This observation indicates that grafting of PMA onto OPEFB impart some flexibility to the blend. The morphology of cryogenically fractured and tensile fracture surfaces of the composites, examined by a scanning electron microscope shows that the adhesion between the fiber and the matrix is improved upon grafting of the OPEFB fiber. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Study on long fiber–reinforced thermoplastic composites prepared by in situ solid‐state polycondensation

Long glass fiber–reinforced thermoplastic composites were prepared by a new process, in situ solid‐state polycondensation (INSITU SSP). In this process reinforcing continuous fibers were impregnated by the oligomer of PET melt, and then the impregnated continuous fibers were cut to a desired length (designated prepreg); finally, the prepreg was in situ polymerized in the solid state to form the high molecular weight matrix. SEM, FTIR spectra, short‐beam shear stress test, flexural strength test, impact strength test, and the intrinsic viscosity measurement were used to investigate the wetting and interfacial adhesion, the mechanical properties of the composite, and the molecular weight of matrix resin in the composite. The results showed that the molecular weight of PET in the matrix resin and mechanical properties could be adjusted by controlling the SSP time and that the high level of interfacial adhesion between reinforcing fibers and matrix resin could be achieved by this novel INSITU SSP process, which are attributed to the good wetting of reinforcing fibers with low molecular weight oligomer melt as the impregnation fluid, the in situ formation of chemical grafting of oligomer chains onto the reinforcing fiber surface, and the in situ formation of the high molecular weight PET chains in the interphase regions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:3959–3965, 2004     

Effects of methyl methacrylate grafting and polyamide coating on the interfacial behavior and mechanical properties of jute‐fiber‐reinforced polypropylene composites

In recent years, environmentally friendly materials have become popular because of the growing environmental demands in human society. Natural fibers are now widely used as reinforcements in polymer matrix composites for their various advantages such as low cost, light weight, abundant resources, and biodegradability. However, the applications of these kinds of composites are limited because of their unsatisfactory mechanical properties, which are caused by the poor interfacial compatibility between the fibers and the thermoplastic matrix. In this paper, three methods, including (i) alkali treatment, (ii) alkali and methyl methacrylate (MMA) treatment, and (iii) alkali and polyamide (PA) treatment (APT), were used to treat jute fibers and improve the interfacial adhesion of jute‐fiber‐reinforced polypropylene (PP) composites (JPCs). The mechanical properties of the JPCs were tested, and their impact fracture surfaces were observed. Infrared spectral analysis showed that MMA was grafted and that PA was coated onto the surface of jute fibers. Mechanical tests indicated that the three kinds of pretreated composites presented better mechanical properties than untreated composites. Among them, the APT composite had the best comprehensive properties. Compared with untreated composites, the tensile strength, flexural strength, and flexural modulus of APT composite were increased by 24.8, 31.3, and 28.4%, respectively. Analysis by scanning electron microscopy showed that better interfacial compatibility between jute fibers and PP occured in this kind of composite. J. VINYL ADDIT. TECHNOL., 2012. © 2012 Society of Plastics Engineers     

Plasma-graft polymerization of vinyl monomers with reactive groups onto a surface of poly(p-phenylene terephthalamide) fiber

The mechanical properties of a fiber-reinforced plastic are influenced by the adhesion between a reinforcing fiber and a matrix resin. In this work we tried to obtain strong adhesion between Kevlar 49^TM yarn and a matrix resin through the formation of covalent bonds. Reactive groups were introduced onto a surface of the yarn by means of plasma-graft polymerization and then reacted with an epoxy resin/curing agent mixture as a matrix resin to form covalent bonds. Glycidyl methacrylate and acrylamide were used as mono-mers for plasma-graft polymerization. The degree of grafting was increased with increasing polymerization time. The grafted yarns enclosed with diglycidal ether of bisphenol-A/tri-ethylenetetramine 2.2 : 1 mixture were pulled out to obtain pull-out force after curing. The pull-out force increased with increasing degrees of grafting. The cóvalent bonds formed between the graft polymer and the matrix resin result in an increment of pull-out force. © 1996 John wiley & Sons, Inc.     

Enhanced mechanical properties of acrylate based shape memory polymer using grafted hydroxyapatite

In the present study, the effect of grafted and ungrafted hydroxyapatite (HAp) filler on the mechanical properties of acrylate based shape memory polymer (SMP) composite is reported. HAp is grafted with polyethylene glycol methacrylate (PEGMA) monomer to avoid agglomeration and the same is embedded as reinforcement in tBA – PEGDMA matrix (70 wt% tBA: tert-butyl acrylate +30 wt% PEGDMA: polyethylene glycol dimethacrylate). The grafting process improved the interfacial interactions of the particles, dispersed in the polymer system and subsequently enhanced the mechanical properties of the shape memory polymer composites. The morphology of HAp particles is investigated by field emission scanning electron microscopy. The mechanical properties of SMP composites are evaluated at room temperature and above glass transition temperature (Tg) with grafted and ungrafted HAp particles. The addition of grafted HAp significantly improved the tensile strength (40%) and shape recovery rate (25%) of the SMP composite when compared to the SMP composite containing ungrafted HAp. SMP composite containing grafted HAp exhibited higher cell viability compared to the neat SMP and the SMP composite containing ungrafted HAp.     

Novel application of chitosan: ameliorative effect of homogeneous and floccular chitosan on the interfacial property of carbon fiber/epoxy resin composites

A novel homogeneous floccular chitosan was directly grafted onto carbon fiber surface by a simple and controllable method. Scanning electron microscopy (SEM), single fiber strengths and interlaminar shear strength (ILSS) have been applied to characterize the fiber and the interface bonding. Compared with raw carbon fibers, the chitosan-treated ones demonstrate significant increases in the surface roughness and wettability. Particularly, about 21.21% increase in the mechanical properties of composites was obtained, which is attributed to good adhesion between functional carbon fiber and resin matrix in the interlaminar regions, as revealed by fracture surfaces.     

Maleic anhydride grafted linear low‐density polyethylene/waste paper powder composites with superior mechanical behavior

The present work aims to study the perspectives of an efficient utilization of waste products as fillers for the thermoplastic polymer. Maleic anhydride grafted linear low‐density polyethylene (LLDPE‐g‐ MA), without any compatibilizers, has been used as polymer matrix to prepare composites with different contents (0–50 phr) of waste paper powder (WPP). Mechanical properties assessment has shown up to 88% improvement in tensile strength and a huge increment of 409% in Young's modulus for the composites prepared at 30 phr WPP. The reinforcement effect of WPP in the polymer matrix was also assessed by Guth‐Gold and modified Guth‐Gold equations. Microstructural analysis of the fractured surfaces revealed good interfacial adhesion with fewer voids and fiber pull out up to 30 phr WPP loading. Interfacial interaction between maleic anhydride group of LLDPE‐g‐ MA and ? OH groups present dominantly in the cellulosic component of WPP was established through Fourier transform infrared spectroscopy. The thermal properties of prepared composites were analyzed by differential scanning calorimetry. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45167.