Thermomechanical properties and rheological behavior of biodegradable composites

The effect of type and content of fillers on the thermal, mechanical, and rheological behavior of the commercial biodegradable polyester product, Ecovio® (BASF) is analytically studied. Ecovio® is basically a blend of poly(butylene adipate‐terephthalate) (PBAT) copolyester (Ecoflex®, BASF) and polylactide (PLA). Two different types of fillers (nanosilica particles and micro‐sized wood‐flour), at various weight fractions were used for this purpose. The role of these fillers on the thermomechanical performance of Ecovio® was investigated in terms of several experimental techniques including scanning electron microscopy (SEM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), creep, tensile testing, and single cantilever bending. The rheological behavior has been systematically analyzed, providing additional evidence about the dispersion quality and the interfacial effects between nanofillers and matrix. One of the findings of this work is that the presence of PBAT in the blend (PLA/PBAT) enhances the compatibility of the polymer matrix with both fillers and their dispersion quality. POLYM. COMPOS., 35:1140–1149, 2014. © 2013 Society of Plastics Engineers     

Mechanical properties and densification behavior of β‐spodumene/anorthite composites

Although β‐spodumene/anorthite composites are interesting systems, little research work has been done to study their properties. This study aims at investigating the preparation and properties of β‐spodumene/anorthite composites containing β‐spodumene proportions ranging between 10 and 25 mass %. X‐ray diffraction analysis (XRD), Scanning electron microscopy (SEM), and the coefficient of thermal expansion (CTE) were used to characterize the effect of addition of β‐spodumene on the phase relations, microstructure, and thermal expansion behavior of resultant composites. The results show that the presence of β‐spodumene significantly reduces the porosity and reduces the densification temperature. It reduces thermal expansion and enhances the mechanical properties of anorthite‐containing composites.     

Mechanical properties and oxidation resistance of SiCf/CVI-SiC composites with PIP-SiC interphase

SiC coatings were successfully synthesized on SiC fibers by precursor infiltration and pyrolysis (PIP) method using polycarbosilane (PCS) as precursor. The morphology of as-fabricated coatings was observed by SEM, and its structure was characterized by XRD and Raman spectrum. The SiC fiber reinforced chemical vapor infiltration SiC (SiC_f/CVI-SiC) composites with PIP-SiC coatings as interphase were fabricated. And, the effects of PIP-SiC interphase on mechanical properties of composites were investigated. The experimental results point out that the coating is smooth and there is little bridging between fibers. The coating is amorphous with SiC and carbon micro crystals. The flexural strength of composites with and without PIP-SiC interphase is 220 and 100 MPa, respectively. And the composites with PIP-SiC interphase obviously exhibit a toughened fracture behavior. The oxidation resistance of composites with PIP-SiC interphase is much better than that of composites with pyrolytic carbon (PyC) interphase.     

MgO-SiC-C复合材料力学性能和抗热震性能研究

对MgO-SiC-C复合材料的力学性能和抗热震性能的研究结果表明SiC含量增加,材料的强度和抗热震性能提高。升温过程中结合剂结构的变化对MgO-SiC-C复合材料强度变化起重要作用。     

Thermosetting polyurethane‐multiwalled carbon nanotube composites: Thermomechanical properties and nanoindentation

In this study, composites based on a thermoset polyurethane elastomer (PU) and multiwalled carbon nanotubes (MWCNT) in the case of a PU of high elastic modulus (>200 MPa) are analyzed for the first time. As‐grown and modified nanotubes with 4 wt % of oxygenated functions (MWCNT‐ox) were employed to compare their effect on composite properties and maxima mechanical properties (elastic modulus and tensile strength) were reached at 0.5 wt % of MWCNT‐ox. Furthermore, by examining the morphology using optical and electron microscopies better dispersion and interaction of the nanotube‐matrix was observed for this material. DMTA data supports the observation of an increase in the glass transition temperature of ～20°C in the nanocomposites compared with the thermoset PU, which is an important result because it shows extended reliability in extreme environments. Finally, nanoindentation tests allowed a comparison with the conventional mechanical tests by measuring the elastic modulus and hardness at the subsurface of PU and the nanocomposites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41207.     

Pinecone particles filled polybenzoxazine composites: Thermomechanical and mechanical properties

In the current study, 1 wt%, NaOH treated pine cone (ATPC) particles composites with bisphenol-A aniline based benzoxazine (BA-a) matrix were prepared by isothermal compression method. Ultimate impacts of ATPC reinforcement on the thermomechanical, tensile, flexural, and impact properties of the composites were studied by using a dynamic mechanical analyzer (DMA), a Universal testing machine, and a Tinius-Olsen impact device, respectively. The thermal stability of ATPC particles was remarkably increased, TGA confirmed that particles will not be degraded during the curing. The DMA results of 30 wt% ATPC reinforced composites confirmed that the glass transition temperature, storage modulus, and loss modulus were 22 ° C, 2510, and 250 MPa higher than the neat matrix, respectively. In addition, the impact strength of the 30 wt% ATPC reinforced composites was nearly 3 times higher than the neat matrix, which confirmed that the matrix's brittleness is reduced, similar observation was confirmed by the Brostow and coworkers empirical model. Moreover, a gradual rise in the tensile and flexural properties was also recorded. We can easily conclude from the studied parameters that the ATPC particles can be used as a sustainable agro-waste in polymeric composites.     

Cellulose fiber-polyester composites with reduced water sensitivity (1)—chemical treatment and mechanical properties

Formaldehyde and di-methylomelamine were used to modify the surfaces of cellulose fibers. Composites were prepared with unsaturated polyester and treated cellulose as the reinforcing material. The tensile strength and the elongation of the cellulose fibers were determined in dry and wet conditions as well as the tensile strength and the tensile modulus of the cellulose-polyester composites. The water uptake of the composites was reduced by 46 to 52 percent. The wet strength of the composites was improved by more than 50 percent.     

Mechanical properties and foaming behavior of cellulose fiber reinforced high‐density polyethylene composites

This article investigates the effects of fiber length and maleated polymers on the mechanical properties and foaming behavior of cellulose fiber reinforced high‐density polyethylene composites. The results from the mechanical tests suggested that long fibers provided higher flexural and impact properties than short fibers. In addition, the maleated high‐density polyethylene increased flexural strength significantly, while the maleated thermoplastic elastormers increased notched Izod impact strength dramatically. On the other hand, the results from the extrusion foaming indicated that the composites with long and short fibers demonstrated similar cell morphology, i.e., a similar average cell size and cell size distribution. However, the addition of maleated high‐density polyethylene caused an increase of the average cell size and cell size distribution in the composites. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Thermo‐mechanical behavior of polyamide 12—polyamide 66 recycled fiber composites

Postconsumed polyamide 66 (PA66) short fibers derived from carpets were utilized as reinforcement in a commercial polyamide (PA12) matrix at different concentrations, ranging from 10 wt% to 30 wt%, in order to evaluate the effect of PA66 content on the mechanical and dynamic behavior of the resulting materials. DSC tests revealed that both melting and crystallization behavior of PA12 matrix was slightly affected by the presence of the fibers, showing a somewhat nucleation effect of PA66. Quasi‐static tensile tests evidenced that the introduction of PA66 fibers provided a slight stiffening effect on the resulting composites, increasing the elastic modulus with the filler content, especially at testing temperatures above T_g. On the other hand, the presence of agglomerated fibers led to an embrittlement of polyamide composites, showing a significant reduction of the tensile properties at break increasing the PA66 fibers content. Tensile dynamic tests confirmed the stiffening effect provided by the recycled fibers, increasing both dynamic moduli (E′ and E″) with PA66 content over the whole range of considered temperatures. Glass transition temperature of PA12 was substantially increased by the presence of the fibers, while the coefficient of linear thermal expansion above T_g was progressively reduced with the filler content. Interestingly, isothermal creep compliance of the material above T_g was substantially reduced by the presence of PA66 fibers. Morphological analysis on the cryofractured surfaces revealed a quite good fiber‐matrix interfacial adhesion, with the presence of some nucleating phenomena on the pulled out surfaces. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Mechanical properties of zirconia composite ceramics

Composite materials based on 8 wt% yttria partially stabilized zirconia, with additions of gadolinium zirconate, lanthanum lithium hexaaluminate, yttrium aluminum garnet and strontium zirconate were characterized. Samples were fabricated by hot-press sintering at 1550 °C. The effect of the secondary phase content on the mechanical properties of the composites was evaluated. Hardness, elastic modulus and fracture toughness of the fabricated composites were determined by means of depth-sensitive indentation testing. The fracture toughness of the samples as determined by the indentation method was found to increase with increasing YSZ content, reaching 3 MPa·m^0.5 for samples with 80 wt% YSZ. The fracture toughness appeared to be affected by thermal expansion coefficient mismatch, crack bridging and crack deflection.     

Mechanical and dielectric properties and crystalline behavior of multilayer graphite-filled polyethylene composites

As one of the duplicated cases of ultrathin polymer films, multilayer graphite/polymer composites are of great interests in various applications. Graphite/polyethylene (PE) composites with various layer numbers and graphite particle sizes were prepared by lamination. The mechanical and dielectric properties and crystalline behavior of the composites were investigated by scanning electron microscopy, differential scanning calorimetry, tensile test, and dielectric strength test. With the same amount of graphite addition, the tensile strength of the composites increases with decreasing layer thickness, but decreases with increasing graphite particle size. The longitudinal tensile strength is greater than the transverse one. The tensile strength of the 3⁶-layer composites with a particle size of 15 μm has enhancements of 34.76 and 68.39% in the longitudinal and transverse directions compared with that of the single-layer pure PE film. The dielectric constant of the composites nonlinearly increases with decreasing layer thickness, while the dielectric loss is independent of this factor. The dielectric constant of the 3⁶-layer composites with a particle size of 15 μm is about two times as large as that of the single-layer pure PE film. The crystalline peak temperature and the crystallinity of the composites increase with the decrease in layer thickness. Coarse-grained molecular dynamics simulations were also carried out to understand the experimental observations by getting an insight into the microstructure of the multilayer composites. This work would be helpful for the production of optimized of multilayer graphite/polymer composites by lamination for electric energy storage. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48131.     

Castor oil‐based polyurethane–polyester nonwoven fabric composites: Mechanical properties,chemical resistance,and water sorption behavior at different temperatures

Castor oil‐based polyurethane (PU)–polyester nonwoven fabric composites were fabricated by impregnating the polyester nonwoven fabric in a composition containing castor oil and diisocyanate. The effects of different diisocyanates such as toluene‐2,4‐diisocyanate (TDI) and hexamethylene diisocyanate (HMDI) on the mechanical properties have been studied for neat PU sheets and their composites with polyester nonwoven fabric. Chemical resistance of the PU composites has been assessed by exposing the specimens to different chemical environments. Percentage water absorption of composites and neat PU sheets has been determined both at room temperature and in boiling water. Both TDI‐ and HMDI‐based PU composites showed a marginal improvement in tensile strength retention at 100°C heat ageing. Water sorption studies were carried out at different temperatures, viz, 30, 50, and 70°C, based on immersion weight gain method. From the sorption results, the diffusion (D) and permeation (P) coefficients of water penetrant have been calculated. Attempts were made to estimate the empirical parameters such as n, which suggests the mode of transport (non‐Fickian), and K, a constant which depends on the structural characteristics of the polymer in addition to its interaction in boiling water. The temperature dependence of the transport coefficients has been used to estimate the activation energy parameters for diffusion (E_D) and permeation (E_p) processes from Arrhenius plots. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Mechanical behavior of CaCO3 particulate-filled β-crystalline phase polypropylene composites

β-crystalline phase polypropylene (PP) composites containing 5, 10, 20, 30, and 40% (by weight) of CaCO₃ filler were prepared by injection molding. The β-form PP was produced by adding a bicomponent β-nucleator consisting of equal amounts of pimelic acid and calcium stearate. The morphology, static tensile, and impact properties of these composites were investigated in this study. Scanning electron microscopy (SEM) observations revealed that the β-spherulites of the polymer matrix of the composites exhibit curved lamellae and sheaf-like structures. The fillers were observed to disperse within the inter-lamellar spacings of the β-PP composite containing 10% calcium carbonate addition. However, the filler particles tend to link together to form larger aggregates when the filler content reaches 20%. Static tensile measurements showed that the elastic modulus of the composites increases with increasing filler content but the yield strength decreases with increasing filler addition. The falling weight Charpy impact test indicated that the β-PP polymer exhibits the highest critical strain energy release rate (G_c) value. However, there was a drastic drop in G_c of the β-PP composites with increasing filler content. The results are discussed and explained in terms of materials morphology.     

Mechanical properties and impact toughness of talc-filled β-crystalline phase polypropylene composites

Injection molded β-crystalline phase polypropylene (PP) composites containing 5, 10, 20, 30 and 40% (by weight) of talc filler were studied by X-ray diffraction, scanning electron microscopy, static tensile and falling drop weight impact tests. The X-ray diffraction analysis showed that the talc filler suppresses the formation of β-form PP dramatically. As a result, the β-PP composites containing talc content ≥20 wt% consisted mainly of the α-form PP phase. The tensile test showed that the addition of talc filler up to 40 wt% leads to an increase in Young's modulus whereas little effect is observed on the yield strength of composites with the addition of talc up to 30%. This behavior can be attributed to the load bearing effect of talc particles with a platelike structure and to good interfacial bonding exists between the matrix and filler. The impact tests revealed that the critical stain energy release rate (G_c) of the β-PP polymers appears to increase initially with the addition of 5 wt% talc; thereafter it decreases significantly with increasing talc content.     

Mechanical behavior of carbon nanofibre‐reinforced epoxy composites

Epoxy resins are widely used in a variety of applications because of their high chemical and corrosion resistance and good mechanical properties. But few types of epoxy resins are brittle and possess low toughness which makes them unsuitable for several structural applications. In this work, carbon nanofibres have been dispersed uniformly into the epoxy resin at a very low concentration (0.07 vol. %). Improvement of 98% in Young modulus, 24% in breaking stress and 144% in work of rupture was achieved in the best sample. The emphasis is on achieving uniform dispersion of carbon nanofibers into epoxy resin using a combination of techniques such as ultrasonication, use of solvent and surfactants. The fracture surfaces of the specimens were studied under scanning electron microscope to see the fracture mechanism of nanocomposites under tensile load and correlate it to the enhancement in their properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Mechanical properties of nickel-powder–filled polypropylene composites

Mechanical properties such as tensile and flexural properties as well as impact behavior of nickel-powder–filled isotactic polypropylene composites were investigated in the composite composition range 0–3.5 volume % Ni. Tensile modulus, strength, and elongation-at-break decreased with increase in Ni content, which is attributed to the introduction of discontinuity in the structure. Analysis of tensile strength data indicated the introduction of stress concentration consequent upon addition of Ni into polypropylene. Izod impact strength at first increased up to a critical Ni content beyond which the value decreased inappreciably while flexural modulus and strength increased with filler concentration.     

Mechanical properties and ablation resistance of HfC nanowire modified carbon/carbon composites

Hafnium carbide nanowires (HfCnws) were in-situ grown in carbon/carbon (C/C) composites, and subsquently the preforms were densified by isothermal chemical vapor infiltration to obtain HfCnws modified carbon/carbon (HfCnws-C/C) composites. Morphology and microstructure of HfCnws were examined, and the effect of HfCnws on the mechanical property and ablation resistance of C/C composites were also investigated. Results show that introducing HfCnws refined the grain size of pyrolytic carbon (PyC). The out-of-plane compression, interlaminar shear and flexual strength of HfCnws-C/C composites increased by 120.80%, 45.60% and 94.65%, respectively compared with pure C/C, and the HfCnws-C/C shows good ablation resistance under oxy-acetylene flame ablation.     

Mechanical properties of modified biofiller‐polypropylene composites

This article reports the mechanical, thermal, and morphological properties of polypropylene (PP)‐chicken eggshell (ES) composites. Mechanical properties like tensile strength, tensile modulus, izod impact strength, flexural modulus of PP composites with normal (unmodified) eggshell and chemically treated ES [modified ES (MES) with isophthalic acid] have been investigated. PP–calcium carbonate (CaCO₃) composites, at the same filler loadings, were also prepared and used as reference. The results showed that PP composites with chemically MES had better mechanical properties compared to the unmodified ES and CaCO₃ composites. An increase of about 3–18% in tensile modulus, 4–44% in izod impact strength and 1.5–26% in flexural modulus at different filler loading was observed in MES composites as compared to unmodified ES composites. Scanning electron microscopy (SEM) micrographs of fractured tensile specimens confirmed better interfacial adhesion of MES with polymer matrix resulting into lower voids and plastic deformation resulting in improved mechanicals of the composites. TEM micrographs showed acicular needle shaped morphology for modified ES and have contributed to better dispersion which is the prime reason for enhancement of all the mechanical properties. At higher filler loading, the modulus of MES composite was found to be higher by 5% as compared to commercial CaCO₃ composites. POLYM. COMPOS., 35:708–714, 2014. © 2013 Society of Plastics Engineers     

Mechanical properties of particulate composites

The mechanical properties of glass bead (30 micron diameter glass spheres) filled epoxy and polyester resins have been studied as a function of volume fraction of filler and the strength of the interfacial bond. The bonding between glass and resin was varied by chemically surface treating the glass using a silicone mold release to prevent chemical bonding at one extreme and a silane coupling agent to maximize bonding at the other extreme. Theoretical predictions of the elastic modulus and tensile strength have been made utilizing a finite element method. Excellent agreement is obtained with the experimental results. Izod impact energies have been measured for these composites as a function of filler content and interface treatment.