Polymer matrix influence on stability of wood polymer composites

The aim of the presented work is to show the influence of the various polymer matrices and the different amounts of the cellulose filler on the composites properties. Samples based on polypropylene, polystyrene, polyoxymethylene, acrylonitrile butadiene styrene, polyester resin, and polylactic acid with different contents of cellulose fibers were prepared by injection molding process. The mechanical and dielectric properties of these composites were studied in order to check whether investigated wood polymer composites fulfill requirements for their application in electrical devices. For all tested composites, a linear increase of modulus with cellulose content was observed. Addition of cellulose to the tested polymers significantly reduces strain at break. In the case of polypropylene and polyoxymethylene composites, the tensile strength increases with the content of the filler. For other materials, there is an inverse relationship, namely the addition of cellulose decreases the tensile strength. The electrical strength decrease was observed with increased cellulose content for the majority of the investigated composites. Polar groups incorporated by cellulose fibers have led to dielectric constant increase. Furthermore, aging of composites in mineral oil and evaluation of water uptake for wood–plastic samples were performed. Wood polymer composites have changed significantly after aging. The water diffusion coefficients were determined, and the significant influence of the amount of cellulose on the water absorption was shown. Copyright © 2015 John Wiley & Sons, Ltd.     

Study on mechanical properties of co-injection self-reinforced single polymer composites based on micro-morphology under different molding parameters

Self-reinforced single polymer composites (SRCs), which are fabricated by combining the same type of polymer with different properties into one body, have high specific strength, no interfacial heterogeneity, and ease of recycling. To better understand the relationship between the micro-morphology and mechanical properties of SRCs, the co-injection molding process was used in this study to process SRCs parts with different molding parameters and obtain the co-injection self-reinforced single polymer composites parts(CI-SRCs parts). Further, the micro-morphology of CI-SRCs parts were observed by polarizing microscope (PLM), scanning electron microscope (SEM), differential scanning calorimetry (DSC) and wide Angle X-ray diffraction (WAXD). From the results, it was found that the tensile properties of CI-SRCs parts with different molding parameters were improved by up to 23.94% compared with the conventional parts. Through PLM observation, it is found that the section shape of CI-SRCs parts perpendicular to the flow direction shows a double ‘skin-core’ structure, and the area ratio of skin layer was higher than that of conventional parts, with a maximum increase of 68%. The low-temperature and low-speed environment were conducive to the formation of skin layer, and the tensile property of CI-SRCs parts were positively correlated with the area ratio of skin layer. SEM was carried out on the skin layer near the fusion position of the interface, and the highly oriented ‘shish-kebab’ structure was observed. The 1D-WAXD pattern analysis shows that the crystallinity of CI-SRCs parts were lower than that of conventional parts, with a maximum reduction of 19.32%. The crystallinity of CI-SRCs parts were positively correlated with melt temperature gradient, and its tensile properties were negatively correlated with the change of crystallinity. The 2D-WAXD pattern analysis shows that the molecular orientation of CI-SRCs parts were higher than conventional parts, with the maximum increase of 37.44%. Low temperature and low speed can improve the molecular orientation of CI-SRCs parts, and the change of molecular orientations were positively correlated with the tensile properties of CI-SRCs parts. By means of response surface method, the molecular orientation obtained was the decisive factor affecting the performance of CI-SRCs parts. Furthermore, by means of the least squares minimization program, the dimensionless equations among molding parameters, micro-morphologies and mechanical properties were established. The prediction of mechanical properties of CI-SRCs parts based on micro-morphologies were realized, providing theoretical support for the ‘adjustability’ of CI-SRCs parts properties.     

E‐glass/DGEBA/m‐PDA single fiber composites: New insights into the statistics of fiber fragmentation

The interfacial shear strength is a critical parameter for assessing composite performance and failure behavior. This parameter is usually obtained from a single‐fiber fragmentation test that induces sequential fracture with increasing strain of a single embedded fiber with output being the distribution of fragment lengths. An exact analytical form for the expected fragment length distribution is still not known. Such data are often fit empirically to Weibull, shifted‐exponential, or lognormal distribution functions. In this report, new insights into the sequential fiber fracture process are provided by detailed analyses of the fiber break locations along the length of the embedded fiber. From this approach, the high degree of uniformity of the break coordinate loci strongly suggests that there can be no mechanistic rationale for the use of the Weibull, or lognormal, or exponential functions to fit the fragment lengths. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2301–2312, 2009     

Photothermal microscopy applied to the study of polymer composites

It is proposed to transfer the capabilities of a high sensitivity photothermal technique, developed by the group and widely used in the study of thermal properties of ceramics, metals and glass, to the study of polymer composites. The technique uses a sensing beam for the measurement of the thermal response of the sample due to local effects induced by heating with a modulated pump laser. With a simple spatial sweep of the beams on the sample surface, information on a micrometric scale of the thermal diffusivity of the material, distribution of phases and pores is obtained. Post-process analysis allows calculating average values of relevant properties such as thermal diffusivity, degree of crystallinity and distribution of aggregates. These measurements are performed at low laser powers (of the order of micro watts) avoiding the damage of the studied samples and turning this technique into a powerful tool of non-destructive characterization.     

Light scattering from swollen textured polymer network composites

Light scattering from a swollen textured heterogeneous polymer network is discussed using example of a network composite filled by spherical inclusions anisotropically distributed in the matrix. The dependence of the scattering intensity on the Fourier transform of the correlation function dry-state shear moduli fluctuations has been established. H_v scattering patterns from uniaxial textures and their ratio with the composite anisotropy parameter are analyzed. The sensitivity of the H_v scattering pattern on restrictions during the swelling is emphasized. © 1993 John Wiley & Sons, Inc.     

Preparation,characterization and properties of fiber reinforced composites using silicon‐containing hybrid polymers

A novel glass fiber reinforced composite was prepared by using silicon‐containing hybrid polymers, poly(methylhydrogen‐diethynylsilyene) (PMES) and poly(phenylethynyl‐silyloxide‐phenylborane) (APABS), as matrix resins. The curing behavior and rheological properties of the matrix resins were investigated by differential scanning calorimetry (DSC) and rotational rheometer. The dynamic viscoelastic properties, mechanical properties, and microstructures of the composites were studied by dynamic mechanical analysis (DMA), universal testing machine (UTM), and scanning electron microscopy (SEM), respectively. The results show that the composite can be well cured between 200 and 300 °C through reactive groups like Si‐H, N‐H, and C≡C units, the possible thermosetting mechanism is also proposed. The composites exhibit excellent mechanical properties with bending strength reach up to 261 and 178 MPa before and after heat‐treating, respectively. SEM analysis clearly indicates that crack in the matrix, matrix/fiber interface debonding, and fiber pull out are predominate failure mechanism for the composites which are heat‐treated in different temperatures. All these obtained results can give theoretical guiding reference for their further applications. Copyright © 2016 John Wiley & Sons, Ltd.     

New PP/PLA/cellulose composites: effect of cellulose functionalization on accelerated weathering behavior (accelerated weathering behavior of new PP/PLA/cellulose composites)

Polylactic acid (PLA) was used as partial replacement for conventional thermoplastic matrix, new composites comprising cellulose, polypropylene (PP), and PLA being realized. In order to obtain a compatible interface between cellulosic pulp and polymeric matrix, two chemical modifications of cellulose with stearoyl chloride and toluene di‐isocyanate (TDI) were performed, structural changes being evidenced by X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The composite materials were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, dynamic scanning calorimetry, impact, tensile and melt rheological tests, surface tension, and dynamic vapor sorption. Because promising results for impact strength and Young modulus were recorded when replacing 15% of PP with PLA in blends of PP with the same cellulosic pulp load, the aim of our study was to assess the behavior to accelerate weathering of composites comprising PP, cellulosic pulp, and PLA. Although the slight decrease in the mechanical properties was recorded after accelerated weathering, the use of functionalized cellulose successfully prevented the deterioration of surface materials, especially for composite comprising stearoyl chloride treated cellulose pulp. Copyright © 2015 John Wiley & Sons, Ltd.     

Mechanical hysteresis,interface and filler–filler structural breakdowns in ethylene vinyl acetate organoclay composites internally lubricated via radiolytically degraded PTFE microparticles

Inclusion of two or more distinct fillers (hybrid fillers) in a matrix is envisaged to entail synergetic advantages. This study reports synthesis and property evaluation of a novel hybrid filler‐based polymer composite containing two types of fillers with distinct attributes namely mechanical reinforcement and internal lubrication. Poly(tetrafluoroethylene) micro‐particles (PTFEMP) were synthesized via radiolytic‐mechanical degradation and used as an internal lubricant for organoclay (OC) reinforced ethylene vinyl acetate (EVA) matrix. Mechanical hysteresis, nonlinear and linear small amplitude oscillatory shear rheology, morphology, small angle X‐ray scattering (SAXS), dynamic coefficient of friction (DCoF), surface wetting and thermoxidative stability of binary and ternary composites were investigated. In EVA/OC composites, PTFEMP acted as an internal lubricant and reduced DCoF in a volume fraction‐dependent fashion. OC and PTFEMP both increased the mechanical hysteresis of EVA; though the magnitude of hysteresis was much less in PTFEMP. Intriguingly, PTFEMP reduced mechanical hysteresis of EVA/OC composites that is work done during loading and unloading stress–strain cycles was considerably reduced with the inclusion of PTFEMP in EVA/OC composites. SAXS results revealed mass fractals and the presence of an interfacial layer in EVA/OC composites but not in EVA/PTFEMP composites. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 509–519     

Influence of heat treatment on electromagnetic properties of polyimide/carbon black composites

A kind of absorbing materials was prepared by hot pressing method using polyimide as matrix and carbon black (CB) as filler. The mechanical properties, the electromagnetic properties, and the thermal stability of polyimide/CB composites were studied. The results showed that the complex permittivity increased from 6.82 + 1.38i to 18.69 + 9.47i, whereas the flexural strength decreased from 108 MPa to 77 MPa, respectively, when the CB content increased from 2 wt% to 8 wt%. The reflection loss curves shifted to low frequency with increase of the thickness at the same content. The reflection loss below ?10 dB could be obtained in the X band with 6 wt% CB content and did not display significant difference before and after the heat treatment at 400°C for 5 h. When the content of CB was 8 wt%, the decomposition temperature (at 5% weight loss) increased approximately 42°C compared with pure polyimide matrix. Copyright © 2014 John Wiley & Sons, Ltd.     

Mechanical property evaluation of glass–jute fiber reinforced polymer composites

The natural fibers such as jute, coir, hemp, sisal etc. are randomly used as reinforcements for composite materials because of its various advantages such as low cost, low densities, low energy consumption over conventional fibers. In addition, they are renewable as well as biodegradable, and indeed wide varieties of fibers are locally available. In this study, glass–jute fiber reinforced polymer composite is fabricated, and the mechanical properties such as tensile, flexural and impact behavior are investigated. The materials selected for the studies were jute fiber and glass fiber as the reinforcement and epoxy resin as the matrix. The hand lay‐out technique was used to fabricate these composites. Fractured surface were comprehensively examined in scanning electron microscope (SEM) to determine the microscopic fracture mode. A numerical procedure based on the finite element method was then applied to evaluate the overall behavior of this composite using the experimentally applied load. Results showed that by incorporating the optimum amount of jute fibers, the overall strength of glass fiber reinforced composite can be increased and cost saving of more than 30% can be achieved. It can thus be inferred that jute fiber can be a very potential candidate in making of composites, especially for partial replacement of high‐cost glass fibers for low load bearing applications. Copyright © 2016 John Wiley & Sons, Ltd.     

The direct architecture of carbon fiber‐carbon nanofiber hierarchical reinforcements for superior interfacial properties of CF/epoxy composites

A simple and efficient chemical method was developed to graft directly carbon nanofibers (CNFs) onto carbon fiber (CF) surface to construct a CF‐CNF hierarchical reinforcing structure. The grafted CF reinforcements via covalent ester linkage at low temperature without any usage of dendrimer or catalyst was investigated by FTIR, X‐ray photoelectron spectroscopy, Raman, scanning electron microscopy, atomic force microscopy, dynamic contact angle analysis, and single fiber tensile testing. The results indicated that the CNFs with high density could effectively increase the polarity, wettability, and roughness of the CF surface. Simultaneous enhancements of the interfacial shear strength, flexural strength, and dynamic mechanical properties as well as the tensile strength of CFs were achieved, for an increase of 75.8%, 21.9%, 21.7%, and 0.5%, respectively. We believe the facile and effective method may provide a novel and promising interface design strategy for next‐generation advanced composite structures.     

Development of flame retarded self-reinforced composites from automotive shredder plastic waste

Multilayered self-reinforced composites were developed from a density-separated light fraction of automotive shredder waste of high polyolefin content, which can fulfil the current technical, safety and environmental requirements of structural materials. The significantly enhanced mechanical properties of the recycled composites were ensured by polypropylene fabric reinforcement; meanwhile, reduced flammability was obtained by modifying the matrix layers, made of secondary raw materials, with phosphorous-containing flame retardant additive. The results of the new flame retarded composite systems allowed the discussion of a novel mechanistic observation. The mechanical and flammability properties of the prepared self-reinforced composites are compared to conventional glass fabric reinforced composites and to compounds without reinforcement.     

Surface modification of carbon fiber for improving the interfacial adhesion between carbon fiber and polymer matrix

In this study, the reinforcing mechanism of amine functionalized on carbon fibers (CFs) has been precisely discussed, and the differences between aliphatic and aromatic compounds have been illustrated. Polyacrylonitrile‐based CFs were functionalized with ethylenediamine, 4,4‐diaminodiphenyl sulphone, and p‐aminobenzoic acid (PAB), and CF‐reinforced epoxy composites were prepared. The structural and surface characteristics of the functionalized CFs were investigated using X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT‐IR), and scanning electron microscopy (SEM). Mechanical properties in terms of tensile and flexural strengths and moduli were studied. The FT‐IR results confirm the success in bonding amines on the CF surface. After treatment of CFs, the oxygen and nitrogen contents as well as the N/C ratio showed an increase. XPS results provided evidence of the chemical reaction during functionalization, rather than being physically coated on the CF surface. Chemical modification of CF with diamines led to considerable enhancement in compatibility of CF filaments and epoxy resin, and remarkable improvements were seen in both tensile and flexural properties of the reinforced composites. SEM micrographs also confirmed the improvement of interface adhesion between the modified CFs and epoxy matrix. Finally, it can be concluded that PAB is a promising candidate to functionalize CF in order to improve interfacial properties of CF/epoxy composites. Copyright © 2015 John Wiley & Sons, Ltd.     

Effect of thermal cycling and open-hole size on mechanical properties of polymer matrix composites

This paper investigates the effects of thermal cycling on mechanical degradation of polymer matrix composites (PMCs). Un-notched and open-hole specimens are tested using developed thermal cycling apparatus and tensile test machine. In addition, the hole-size effect of open-hole tension glass/epoxy composite laminates is investigated. The tensile strength, mass loss and surface degradation of the specimens were obtained during 250 cycles. Experimental results showed that the holes diameter is the main parameter to control the thermal cycling effects on open hole structure. Also, it is found that laminates with smaller holes have higher tensile strength variation than those with larger holes. The results showed that increment of the hole diameter and number of cycles decreases the tensile strength.     

Completely biodegradable composites of poly(propylene carbonate) and short,lignocellulose fiber Hildegardia populifolia

The composites of biodegradable poly(propylene carbonate) (PPC) reinforced with short Hildegardia populifolia natural fiber were prepared by melt mixing followed by compression molding. The mechanical properties, thermal properties, and morphologies of the composites were studied via static and dynamic mechanical measurements, thermogravimetric analysis, and scanning electron microscopy (SEM) techniques, respectively. Static tensile tests showed that the stiffness and tensile strength of the composites increased with an increasing fiber content. However, the elongation at break and the energy to break decreased dramatically with the addition of short fiber. The relationship between the experimental results and the compatibility or interaction between the PPC matrix and fiber was correlated. SEM observations indicated good interfacial contact between the short fiber and PPC matrix. Thermogravimetric analysis revealed that the introduction of short Hildegardia populifolia fiber led to a slightly improved thermooxidative stability of PPC. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 666–675, 2004     

Improved mechanical properties of epoxy‐based composites with hyperbranched polymer grafting glass‐fiber

A glass‐fiber, grafted by hyperbranched polymer with hydroxyl group (GF‐HBPH), reinforced epoxy‐based composite was evaluated for mechanical properties and compared with the neat epoxy and silanized glass‐fiber, GF‐APS. The epoxy/GF‐HBPH composites were studied by attenuated total internal reflectance infrared spectroscopy, ¹H nuclear magnetic resonance spectroscopy, thermal gravimetric analysis, mechanical properties analysis, and field emission‐scanning electron microscopy. The results showed that the incorporation of GF‐HBPH could simultaneously enhance the mechanical properties of the epoxy composites. Field emission‐scanning electron microscopy images of the fracture surfaces of the test specimens were used to support the results and conclusions. Copyright © 2016 John Wiley & Sons, Ltd.     

Dielectric properties and molecular mobility of organic/inorganic polymer composites

Microstructure-dielectric properties relationship and molecular mobility of organic/inorganic polymer composites (OIPCs), consisting of polyurethane (PU) and sodium silicate (NaSi), were investigated in this work. Broadband dielectric relaxation spectroscopy (DRS) and thermally stimulated depolarization current (TSDC) techniques were employed. Our interest was focused on the study of the glass transition mechanism and conductivity relaxation. The influence of the molecular weight of PU and inorganic phase content on the dielectric properties of the composites was of particular interest. Glass transition temperature shifts to higher temperatures with the addition of NaSi. The overall molecular mobility was found to increase in the composites, compared to the pure PU matrix. The results are more intense for the composites based on the PU with low molecular weight.     

Design of thermal hybrid composites based on liquid crystal polymer and hexagonal boron nitride fiber network in polylactide matrix

Development of high thermally conductive and electrically insulative composites is of interest for electronic packaging industry. Advancements in smaller and more compact electronic devices required improvements in packing materials, including their weight, thermal conductivity, and electrical resistivity. In addition, with the increasing environmental awareness, the usage of green (bio‐based) alternatives was equally important. In the present study a hybrid based on fibers of highly concentrated hexagonal boron nitride (hBN) in liquid crystal polymer (LCP) matrix were fabricated. These hybrids were formed by arranging hBN platelets into LCP fiber form to reach high filler concentration and then randomly mix it in polylactide (PLA) matrix. With appropriate filler interaction within the hybrid, thermal conductivity similar to that of pure fiber could be achieved. Filler interaction may be tailored by optimizing the fibers aspect ratio. This study demonstrated the effect of random fillers in fibers shape in increasing the overall thermal conductivity of PLA polymeric hybrid using hBN and LCP fibers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 457–464     

An approach to one‐dimensional conductive polymer composites

A substantial approach to one‐dimensional (1D) electrically conductive composites was proposed which was based on the thermodynamic analysis of electric‐field‐induced particle alignment in a nonpolar thermoplastic polymer matrix. The process condition window was based on the real‐time exploration of dynamic percolation under different electric fields with carbon black (CB)‐filled polyethylene as a model. The CB content was the main factor of the process condition. Its upper limit was set as the critical percolation concentration at the thermodynamic equilibrium state without an electric field to eliminate the possibility of conductive network formation perpendicular to the electric‐field direction, whereas its lower limit the critical percolation concentration at the thermodynamic equilibrium state under a critical electric field (E*). A composite with CB content in this window, isothermally treated in an electric field not less than E*, showed conductivity in the electric‐field direction about 10⁵ times larger than that in the perpendicular direction. A 1D cluster structure in the direction of the electric filed was confirmed with scanning electron microscopy morphology observations. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 184–189, 2005     

Nanocellulose reinforced as green agent in polymer matrix composites applications

Owing to their abundance, high strength and stiffness, and low weight and biodegradability, nanocellulose (NC) is regarded as a promising candidate for the preparation of green composites. The high reinforcing effect assigned to the mechanical percolation phenomenon of NC is due to the stiff continuous networks of cellulosic nanoparticles linked via hydrogen bonding. Compared to nanocrystalline cellulose, NC fibers result in more significant improvement to the modulus, stiffness, and strength as aspect ratio NC fiber is higher compared to NC crystal. Indeed, in the case of biopolymer composites, the reinforcement effect of NC is attributed to the NC‐polymer interactions and the reinforcing effect occurring through effective stress transfer at the NC‐polymer interface. The NC‐reinforced composites tend to become more brittle as the concentration of the reinforcing particles increase up to the saturated level, due to the reduction in surface adhesion between filler and matrix. Due to its promising mechanical and structural stability, NC composites have been used widely in many industrial applications such as food packaging, electronic applications, and tissue engineering.