Morphology and tensile properties of unreinforced and short carbon fibre reinforced Nylon 6/multiwalled carbon nanotube-composites

The morphology and the tensile properties of unreinforced and short carbon fibre (SCF) reinforced Nylon 6/multiwalled carbon nanotube (MWCNT)-composites are investigated. The morphology analysis shows that MWCNT and SCF are randomly oriented in the composites. Furthermore, the SCF fail due to fibre pull-out, while the MWCNT fail due to fracture. Young's modulus and tensile strength of SCF reinforced Nylon 6 and Nylon 6/MWCNT-composites increase with increasing total filler volume content. Replacing SCF by MWCNT further enhances Young's modulus and the tensile strength. An additive modelling approach leads to better results at low MWCNT-volume contents, while at higher MWCNT loadings a multiplicative modelling approach results in a better approximation of the experimental data. Thus the SCF reinforced Nylon 6/MWCNT-composites behave at low MWCNT-volume contents like a polymer composite containing two different types of fillers, while at higher MWCNT loadings a behaviour of a short fibre reinforced nanocomposite is observed.     

Mechanisms of fracture and prediction of the strength of unidirectional carbon-fibre-reinforced plastics

The principal difference in the mechanisms of fracture of unbound carbon fibres and reinforcing filler in unidirectional carbon-fibre-reinforced plastics does not allow predicting the strength of composites using Weibull distribution parameters and the average strength of the fibres on a standard testing base. An alternative approach that allows estimating the limiting strength of carbon fibres and the degree of its realization in a composite was repeatedly tested. The dependence of the strength realization coefficient of a reinforcing fibre on its volume content, the scaling effect of the strength, and the modulus of elasticity is given. The information required for predicting the strength of composites could be obtained from testing composites with a single fibre (SFC tests). __________ Translated from Khimicheskie Volokna, No. 1, pp. 51–57, January–February, 2006.     

Physicomechanical Properties of Carbon-Containing Film Composite Materials

Addition of 5 to 20% carbon filler to film composite material (FCM) decreases its strength and mechanical modulus of elasticity. Addition of porous carbon fillers (Aktilen fibre, industrial carbon, activated carbon) decreases the physicomechanical properties of FCM even at a low content, under 5%. FCM made from a liquid composition and containing carbon fibres exhibit anisotropy of the mechanical properties due to orientation of the filler; the strength and modulus of elasticity are higher in the longitudinal than in the transverse direction. A hypothesis is advanced concerning the presence of defective regions on the polymer—filler interface and stress concentration on the ends of the fibres, which probably also causes the decrease in the mechanical properties of the FCM. Acoustic studies suggested the existence of contacts between the carbon fibres at a content in FCM of 10% and higher. __________ Translated from Khimicheskie Volokna, No. 4, pp. 52–55, July–August, 2005.     

Mechanical behavior of nylon composites containing talc and kaolin

Particulate reinforced thermoplastic composites are designed to improve the properties and to lower the overall cost of engineering plastics. In this study, the influence of adding talc and kaolin fillers on the mechanical properties of nylon 6 was investigated. Fillers, either singly or mixed by various weight ratios between 10 and 30 wt %, were added to nylon 6. Test samples of the composite material were prepared by the injection‐molding process. Uniaxial tensile and Izod impact tests were carried out. Tensile strength, elongation at break, modulus of elasticity, and impact energy were obtained. The results showed that the tensile strength and modulus of elasticity of nylon 6 composite increased with the increase in filler ratio, whereas the impact strength and maximum elongation decreased with the increase in filler ratio. The optimal nylon composite was determined with the addition of a 10 to 15 wt % filler ratio. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1694–1697, 2003     

Hemp fibre as alternative to glass fibre in sheet moulding compound Part 1 – influence of fibre content and surface treatment on mechanical properties

Abstract

Hemp fibre mat reinforced unsaturated polyester composites were fabricated using a conventional sheet moulding compound process. The influence of fibre and CaCO₃ filler content on strength and stiffness of these hemp fibre reinforced sheet moulding compounds is reported and compared with data for chopped glass fibre reinforced sheet moulding compounds. In addition the influence of alkaline and silane treatments of the hemp fibres is evaluated. The experimental data are compared to modified versions of the Cox–Krenchel and Kelly–Tyson models, supplemented with parameters of composite porosity to improve the prediction of composite tensile properties. A good agreement was found between the modified models and experimental data for strength and stiffness. The results indicate that hemp fibre reinforced sheet moulding compounds are of interest for low cost engineering applications that require high stiffness to weight ratios.     

Evaluation of dynamic elastic properties of wood‐filled polypropylene composites

Dynamic modulus of elasticity (MoE) and shear modulus of wood‐filled polypropylene composite at various filler contents ranging from 10% to 50% was determined from the vibration frequencies of disc‐shaped specimens. Wood filler was used in both fiber form (pulp) and powder form (wood flour). A novel compatibilizer, m‐isopropenyl‐α,α‐dimethylbenzyl‐isocyanate(m‐TMI) grafted polypropylene with isocyanate functional group was used to prepare the composites. A linear increase in dynamic MoE, shear modulus, and density of the composite was observed with the increasing filler content. Between the two fillers, wood fiber filled composites exhibited slightly better properties. At 50% filler loading, dynamic MoE of the wood fiber filled composite was 97% higher than that of unfilled polypropylene. Halpin‐Tsai model equation was used to describe the changes in the composite modulus with the increasing filler content. The continuous improvement in elastic properties of the composites with the increasing wood filler is attributed to the effective reinforcement of low‐modulus polypropylene matrix with the high‐modulus wood filler. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1706–1711, 2006     

Effect of alkali treatment on properties of unidirectional isora fibre reinforced epoxy composites

Abstract

Unidirectional isora fibre reinforced epoxy composites were prepared by compression moulding. Isora is a natural bast fibre separated from Helicteres isora plant by retting process. The effect of alkali treatment on the properties of the fibre was studied by scanning electron microscopy (SEM), IR, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Mechanical properties such as tensile strength, Young's modulus, flexural strength, flexural modulus and impact strength of the composites containing untreated and alkali treated fibres have been studied as a function of fibre loading. The optimum fibre loading for tensile properties of the untreated fibre composite was found to be 49% by volume and for flexural properties the loading was optimised at ～45%. Impact strength of the composite increased with increase in fibre loading and remained constant at a fibre loading of 54·5%. Alkali treated fibre composite showed improved thermal and mechanical properties compared to untreated fibre composite. From dynamic mechanical analysis (DMA) studies it was observed that the alkali treated fibre composites have higher E' and low tan δ maximum values compared to untreated fibre composites. From swelling studies in methyl ethyl ketone it was observed that the mole percentage of uptake of the solvent by the treated fibre composites is less than that by the untreated fibre composites. From these results it can be concluded that in composites containing alkalised fibres there is enhanced interfacial adhesion between the fibre and the matrix leading to better properties, compared to untreated fibre composites.     

Resonant frequency study of tensile and shear elasticity moduli of carbon fibre reinforced composites (CFRC)

The dynamic elastic properties are important characteristics of composite materials. They control the vibrational behaviour of composite structures and are also an ideal tool for monitoring of the development of CFRCs’ mechanical properties during their processing (heat treatment, densification). The present studies have been performed to explore relations between the dynamic tensile and shear moduli and some structural features (viz., fibre fraction, fibre type, porosity, weave pattern of woven reinforcement) of various unidirectional or bi-directional fibre reinforced carbon/carbon composites, made out of PAN- or pitch-based fibres as reinforcements and phenolic resin or coal tar pitch as matrix precursors. The dynamic tensile and in-plane shear moduli were determined from resonant frequencies of a beam with free ends. The longitudinal dynamic Young’s modulus of unidirectional CFRC composites – besides its dependence on the original fibre modulus and fibre volume contents – also reflects changes induced in matrix and fibres by heat treatment. The in-plane shear modulus does not depend on the fibre type but there exists its distinct tendency to increase with increasing fibre fraction. For bi-directionally reinforced composites, the longitudinal tensile modulus is more sensitive to the fabric weave pattern than to the fibre type. Tensile modulus of diagonally cut specimens and in-plane shear modulus of longitudinally cut ones are mutually correlated and, therefore, simultaneously controlled by densification steps and graphitisation heat treatment.     

Tensile behavior of unidirectional polyethylene fibers PMMA and glass fibers—PMMA composite laminates

Unidirectional (UD) composite laminates based on glass fibers (GF) and high‐performance polythylene fibers (PEF) were prepared with partially polymerized methyl methacrylate (MMA) at room temperature, followed by heating at 55°C (well below the softening point of PEF) for 2 h. The tensile strength, modulus of elasticity, fiber efficiency and strength efficiency of both the composite laminates, loaded parallel to the fibers, at the same volume fraction range, were investigated. All the properties were compared between the two composite laminates. It was observed that the measured tensile strength and modulus of elasticity deviated from the values calculated from the Rule of Mixture (ROM). The deviation was minimal at the lower volume fraction of fibers, and increased with the fiber volume. An interesting feature that was observed was that the efficiencies of PEF‐reinforced composite was higher than that of the GF‐reinforced composite at the same volume fraction of the fibers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1489–1493, 2000     

Thermal and mechanical properties of aluminum powder-filled high-density polyethylene composites

Thermal conductivity and mechanical properties such as tensile strength, elongation at break, and modulus of elasticity of aluminum powder-filled high-density polyethylene composites are investigated experimentally in the range of filler content 0–33% by volume for thermal conductivity and 0–50% by volume for mechanical properties. Experimental results from thermal conductivity measurements show a region of low particle content, 0–12% by volume, where the particles are distributed homogeneously in the polymer matrix and are not interacting with each other; in this region most of the thermal conductivity models for two-phase systems are applicable. At higher particle content, the filler tends to form ag-glomerates and conductive chains resulting in a rapid increase in thermal conductivity. The model developed by Agari and Uno estimates the thermal conductivity in this region. Tensile strength and elongation at break decreased with increasing aluminum particles content, which is attributed to the introduction of discontinuities in the structure. Modulus of elasticity increased up to around 12% volume content of aluminum particles. Einstein's equation, which assumes perfect adhesion between the filler particles and the matrix, explains the experimental results in this region quite well. For particle content higher than 30%, a decrease in the modulus of elasticity is observed which may be attributed to the formation of cavities around filler particles during stretching in tensile tests. © 1996 John Wiley & Sons, Inc.     

Viscoelastic and mechanical characterization of graphene decorated with graphene quantum dots reinforced epoxy composites

The article explores viscoelastic and mechanical property analysis of graphene decorated with graphene quantum dots (GDGQD) reinforced epoxy composite. Tensile, nanoindentation, and nano-dynamic mechanical analysis (DMA) tests were conducted on the composite with 0 to 1 wt% filler variation (an interval of 0.25 wt% maintained). The hardness and elastic modulus for two different loading conditions under a frequency range of 10 to 250 Hz were performed. The viscoelastic properties described through loss tangent and storage modulus graphically and the various factors such as modulus and depth of penetration were influenced by force frequency and mobility of the molecular chain. The results revealed the role of GDGQDs as filler material for enhancing the nanomechanical and tensile properties of the epoxy matrix. The differences in the properties can be ascribed to the filler interfacial bonding with the polymer matrix at the molecular level. The macro-level properties like tensile properties following the same trend as that of the micro-level properties like nano-indentation and nano-DMA results. Further, with the GDGQD aspect ratio, and assuming three-dimensionally filled randomly orientation of filler, the Halpin-Tsai model was satisfied with the experimental tensile modulus values.     

Effect of aging on the compressive yielding of PAN-based carbon fiber/polycarbonate composites

The compressive yield behavior and the effect of aging in boiling water on the mechanical properties of polycarbonate composites reinforced with PAN-based carbon fibers were studied at different filler contents and over a range of strain rates. The Young's modulus, yield stress, and yield strain are reported as a function of aging time. Other mechanical parameters such as the activation energy and volume of the yielding process were determined through the Eyring theory. The increase of both Young's modulus and yield stress with aging in boiling water is explained by structural changes. The mechanical properties of the composite were correlated with the morphology and its glass transition temperature.     

Mechanical properties and morphology of nylon‐6 hybrid composites

In this investigation, the influence of filler type and filler content on the mechanical properties of nylon‐6 is investigated. The mineral fillers were selected on the basis of their shape and size: flake‐like kaolin and talc, spherical glass beads or fibrous wollastonite. These fillers were added to nylon‐6 individually or in mixed combinations. They were added at different percentages varying between 10 and 30% w/w. Samples of the composites were prepared by the injection moulding process. Uniaxial tensile, Izod impact and flexural tests were carried out. Tensile strength, elongation at break, modulus of elasticity and impact energy were obtained and compared. In case of single fillers the results showed that the tensile strength, modulus of elasticity and their flexural values for nylon‐6 composite improve with the increase in filler content while mixed compounds showed no significant changes above 15% + 15% w/w filler. However, for single and mixed filler up to 10% w/w, the impact strength and maximum elongation at break showed significant decrease. In general, the maximum improvement in mechanical the addition of 10–15% w/w filler. Copyright © 2003 Society of Chemical Industry     

The effect of reinforcement volume fraction and particle size on the mechanical properties of β-tricalcium phosphate–high density polyethylene composites

The mechanical properties of the tricalcium phosphate–high density polyethylene (β-TCP/HDPE) composite samples have been investigated by looking at the effect of particle size and volume fraction of tricalcium phosphate on the fracture strength, modulus of elasticity and failure energy in the composite samples. A decrease in both the fracture strength and failure energy was observed with an increase in the volume fraction of the tricalcium phosphate. Both properties decreased further with the use of larger β-TCP particles. Increase in the tricalcium phosphate content led to an increase in the modulus of elasticity values in the composite samples. However, a lesser increase in modulus of elasticity was observed when larger β-TCP particles were used in the preparation of the composite samples. SEM analysis of the fractured surfaces showed a transition from ductile to brittle type of failure as the volume fraction of the tricalcium phosphate increased in the samples.     

Development of Silicon Carbide Reinforced Jute Epoxy Composites: Physical,Mechanical and Thermo-mechanical Characterizations

The aim of the present study was to investigate the physical and thermo-mechanical characterization of silicon carbide filled needle punch nonwoven jute fiber reinforced epoxy composites. The composite materials were prepared by mixing different weight percentages (0–15 wt.%) of silicon carbide in needle punch nonwoven jute fiber reinforced epoxy composites by hand-lay-up techniques. The physical and mechanical tests have been performed to find the void content, water absorption, hardness, tensile strength, impact strength, fracture toughness and thermo-mechanical properties of the silicon carbide filled jute epoxy composites. The results indicated that increase in silicon carbide filler from 0 to 15 wt.% in the jute epoxy composites increased the void content by 1.49 %, water absorption by 1.83 %, hardness by 39.47 %, tensile strength by 52.5 %, flexural strength by 48.5 %, and impact strength by 14.5 % but on the other hand, decreased the thermal conductivity by 11.62 %. The result also indicated that jute epoxy composites reinforced with 15 wt.% silicon carbide particulate filler presented the highest storage modulus and loss modulus as compared with the unfilled jute epoxy composite.     

Mechanical properties of polypropylene composites reinforced with long glass fibres and mineral fillers

Abstract

The mechanical behaviour of long discontinuous glass fibre (LGF) reinforced polypropylene (PP) composites filled with talc or calcium carbonate fillers was studied. Sample specimens were processed by injection moulding, after which tensile and impact properties were analysed. In addition, scanning electron microscopy was used to analyse the morphology of the fracture surfaces. The results showed that the use of talc as a hybrid filler in LGF reinforced PP leads to a better tensile strength and toughness than in a corresponding hybrid composite based on calcium carbonate. Furthermore, it was observed that the matrix had a dominant role at low fibre content, whereas at high fibre loading, the effect of fibres was more evident.     

Curing Characteristics and Mechanical Properties of Oil Palm Wood Flour Reinforced Epoxidized Natural Rubber Composites

Abstract

The paper reports on the curing characteristics and mechanical properties of oil palm wood flour (OPWF) reinforced epoxidized natural rubber (ENR) composites. Three sizes of OPWF at different filler loadings were compounded with a two roll mill. The cure (t ₉₀) and scorch times of all filler size decrease with increasing OPWF loading. Increasing OPWF loading in ENR compound resulted in reduction of tensile strength and elongation at break but increased tensile modulus, tear strength and hardness. The composites filled with smaller OPWF size showed higher tensile strength, tensile modulus and tear strength. Scanning electron microscope (SEM) micrographs showed that at lower filler loading the fracture of composites occurred mainly due to the breakage of fibre with minimum pull-out of fibres from the matrix. However as the filler loading is increased, the fibre pull-out became very prominent due to the lack of adhesion between fibre and rubber matrix.     

Reinforcement effect of biomass carbon and protein in elastic biocomposites

Biomass carbon (BC) and soy protein (SP) were used to reinforce natural rubber (NR) biocomposites. The particle size of BC was reduced and characterized with elemental analysis, X‐ray diffraction, infrared spectroscopy, and particle size analysis. The rubber composite reinforced with the BC/SP and the composite reinforced with the BC of higher carbon content show useful tensile properties at an optimum filler fraction. The model analysis of the stress–strain behaviors provides insight into filler network characteristics. For the highly filled composites, the BC have less constraint on the polymer chains as shown by the temperature and frequency dependent modulus as well as the model analysis of stress softening effect. The presence of NR protein improves the filler–polymer adhesion for the composites reinforced with BC/SP. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Elasticity and structure of weak graphite nanoplatelet (GNP) networks in polymer matrices through viscoelastic analyses

The elasticity and structure of graphite nanoplatelets networks in polymer matrices are studied through linear viscoelastic analyses. GNPs-filled polystyrene nanocomposites at different filler content are prepared through a combination of solution and melt mixing techniques. Electrical volume conductivity experiments prove that a continuous path of conductive nanoplatelets builds up across the matrix above a critical filler content. GNP networks, however, are too tenuous to be detected through conventional dynamic-mechanical spectroscopy in the melt state. Nevertheless, we are able to estimate their elasticity by exploiting the predictive feature of a simple two-phase rheological model. Our approach, validated through the building of a master curve of the elastic modulus of samples at different composition, allows to isolate the elastic contribution of the bare GNP network, whose dynamics reveal that its elasticity follows critical behaviour as predicted by percolation theory.     

Bio‐polyester–date seed powder composites: Morphology and component migration

Biodegradable polyesters poly‐l ‐lactide (PLA) and poly(butylene adipate‐co‐terephthalate) (PBAT) were reinforced with varying amount of date seed powder (DSP) with an aim to utilize the date seed waste as well as to achieve composites with improved properties. The PLA composites exhibited increase in the elastic response over the viscous response as a function of filler fraction, whereas the PBAT composites retained the viscous dominance irrespective of DSP content. The tensile modulus of the PBAT composites had enhancement of more than 300% in the composite with 40% filler content. The PLA composites also enhanced the modulus marginally till 20% filler content, however, it was still significant because of the very high modulus of PLA as compared to PBAT. Thermal analysis also indicated the stability of the composite, thus, confirming the usefulness of DSP as filler for the polymers. The TEM and light microscopy characterization revealed presence of voids in the composites which were present around the filler particles as well as dispersed in the polymer matrix. Such features were confirmed through TGA‐MS to be resulting from the escape of water vapor bound in DSP. The composites with 10% DSP content had lower extent of such voids and the morphology remained relatively unchanged with time. In the composites with 30% DSP content, in the seasoned sample, a soft and sticky phase resulting from the surface migration of date seed oil was also observed. The generation of the soft phase was also a slow process as 24 h were not enough to generate this phase. The migration of the oil to the surface was also confirmed by the IR and X‐ray diffraction studies. After embedding in compost soil, the PLA composite with 40% filler content had nine times more biodegradation after 120 days as compared to pure polymer, whereas it was 11 times for PBAT composite with same filler content. It confirmed that the addition of DSP did not lead to any thermal and mechanical degradation of the bio‐polyesters and resulted in enhanced mechanical and biodegradation behavior along with oil migration. The controlled component migration can lead to potential generation of commercially important self‐lubricating composite materials. POLYM. ENG. SCI., 55:877–888, 2015. © 2014 Society of Plastics Engineers