Inclusion of graphene on low-density polyethylene composite properties

Graphene (Gr) distribution in low‐density polyethylene (LDPE) and ethylene vinyl acetate (EVA) considerably increased thermal stability and mechanical properties of LDPE/Gr or EVA/Gr composites. Dynamic mechanical analysis (DMA) and strength testing machine were used to study mechanical properties. The high specific surface areas and superior properties of Gr improved thermal strength, storage modulus, and mechanical properties of composites. Outstanding distribution of Grs was accomplished and verified by atomic force microscopy. LDPE/Gr and EVA/Gr composites were characterized by transmission electron microscope (TEM), X‐ray diffraction, and thermogravimetric analyses to study the distribution morphology and thermal strength. Results display that the presence of filler does not create an alteration in the microscopic structure of polymers. Measurement of tensile properties shows that the tensile strength of composites contains Gr is significantly higher than similar values for pure EVA and LDPE. The DMA shows that the storage modulus of composites is much greater than that of pure EVA and LDPE. The thermal stability of the composite contains Gr is also considerably higher than that of pure EVA and LDPE. J. VINYL ADDIT. TECHNOL., 24:E177–E185, 2018. © 2018 Society of Plastics Engineers

The logical outline and assembly of structural–functional materials are progressive tendencies of materials knowledge. In this study, it was found that the homogenous graphene (Gr) spread in low-density polyethylene (LDPE) considerably increases the mechanical properties of LDPE/Gr composites. The high specific surface areas and superior properties of Gr improved thermal strength, conductivity, storage modulus, and mechanical properties of composites. Results display that the inclusion of Gr (0–3 wt.%) and frequency growth enhanced the viscosity, loss modulus, and storage modulus of LDPE/Gr composites significantly. The addition of Gr also augmented the Young’s modulus, Young’s strength, tensile modulus, and elongation modulus, but the tensile strength values of LDPE/Gr composites have not changed significantly. The elongation test displayed reduction values with further addition of Gr in LDPE/Gr composites. The effect of temperature rise caused the decrease in the storage modulus with Gr addition; however, further inclusion of Gr mitigated the trend of storage modulus reduction of the composites considerably. This study also presents that Gr inclusion leads to limit polymer chain mobility, which reduces maximum strain and increases the melt flow indexes during material processing.

Graphene (Gr) distribution in low-density polyethylene (LDPE) considerably increased thermal stability, thermal conductivity, mechanical properties, and flexural properties of LDPE/Gr composites. Addition of Grs to LDPE postponed the time for making the polymer brittle. High specific surface area and superior properties of Gr improved thermal stability, conductivity, storage modulus, and mechanical properties of composites. The electrical conductivity of LDPE/Grs composites upgraded owing to the thermal stability of Grs in LDPE matrix. In terms of rheology, the addition of Grs augmented viscosity of the LDPE matrix. Addition of Grs to LDPE nucleates crystallization by reducing the activation energy along with rising crystallization onset temperature. Adding Gr facilitated decreasing aggregation, expanded crystallinity, improved the local lattice order of LDPE/Grs, and advanced Grs contact with LDPE. Thus, on a macroscopic scale, Gr constrains mobility of polymer chains, causing a growth in stiffness and strength of the composite. The distribution of Grs in LDPE at micron size scale was verified by atomic force microscopy and other microscopic testers. With further Grs inclusions to LDPE, the activation energy reduced, Grs proceeded as nucleating agents throughout the crystallization of composites, and increased the enhancement of relative crystallinity of LDPE/Gr compounds. The percolation phenomenon of LDPE/Gr composite occurred about 0.5 wt% of Gr loading. Due to further addition of Gr to LDPE, the impermeability of oxygen through the conduit raised somehow the LDPE/Gr sample with 0.5 wt% Gr content, generated a sharp improvement, and dropped fuel permeation with about 37% in comparison with pure LDPE.

Recent years have witnessed a growing research interest in graphene-reinforced alumina matrix composites (Al2O3-G). In this paper, to better achieve the dispersion of graphene in composites, a ball milling method for adding raw materials step by step, called stepwise feeding ball milling, was proposed. The Al2O3-1.0 wt % graphene composites were prepared by this stepwise feeding ball milling and hot pressing. Then, the effects of sintering temperature and sintering pressure on the microstructure and mechanical properties of composites were studied. Results showed that the bending strength, fracture toughness and Vickers hardness of composites increased firstly and then decreased with increasing sintering temperature. The mechanical properties of composites were all at their maximum with the sintering temperature of 1550 °C. For example, the bending strength of composites reached 754.20 MPa, which was much bigger than 478.03 MPa at 1500 °C and 364.01 MPa at 1600 °C. Analysis suggested that the strength of composites was mainly related to the grain size, microflaw size and porosity.

Modern electronics not only require the thermal management ability of polymer packaging materials but also need anti-voltage and mechanical properties. Boron nitride nanosheets (BNNS), an ideal thermally conductive and high withstand voltage (800 kV/mm) filler, can meet application needs, but the complex and low-yield process limits their large-scale fabrication. Herein, in this work, we prepare sucrose-assisted ball-milled BN(SABM-BN)/polyetherimide (PEI) composite films by a casting-hot pressing method. SABM-BN, as a pre-ball-milled filler, contains BNNS and BN thick sheets. We mainly investigated the thermal conductivity (TC), breakdown strength, and mechanical properties of composites. After pre-ball milling, the in-plane TC of the composite film is reduced. It decreases from 2.69 to 2.31 W/mK for BN/PEI composite film at 30 wt% content; however, the through-plane TC of composites is improved, and the breakdown strength and tensile strength of the composite film reach the maximum of 54.6 kV/mm and 102.7 MPa at 5 wt% content, respectively. Moreover, the composite film is used as a flexible circuit substrate, and the working surface temperature is 20 ℃, which is lower than that of pure PEI film. This study provides an effective strategy for polymer composites for electronic packaging.

The massive accumulation of plastic waste has caused a serious negative impact on the human living environment. Replacing traditional petroleum-based polymers with biobased and biodegradable poly(l-lactic acid) (PLLA) is considered an effective way to solve this problem. However, it is still a great challenge to manufacture PLLA-based composites with high thermal conductivity and excellent mechanical properties via tailoring the microstructures of the blend composites. In the present work, a melt extrusion-stretching method is utilized to fabricate biodegradable PLLA/poly(butylene adipate-co-butylene terephthalate)/carbon nanofiber (PLLA/PBAT/CNF) blend composites. It is found that the incorporation of the extensional flow field induces the formation of multioriented microstructures in the composites, including the oriented PLLA molecular chains, elongated PBAT dispersed phase, and oriented CNFs, which synergistically improve the thermal conductivity and mechanical properties of the blend composites. At a CNF content of 10 wt %, the in-plane thermal conductivity, tensile strength, and elongation at break of the blend composite reach 1.53 Wm-1 K-1, 66.8 MPa, and 56.5%, respectively, which increased by 31.9, 73.5, and 874.1% compared with those of the conventionally hot-compressed sample (1.16 Wm-1 K-1, 38.5 MPa, and 5.8%, respectively). The main mechanism for the improved thermal conductivity is that the multioriented structure promotes the formation of a CNF thermal conductive network in the composites. The strengthening mechanism is attributed to the orientation of both PLLA molecular chains and CNFs in the stretching direction, restricting the movement of PLLA molecular segments around CNFs, and the toughening mechanism is due to the transformation of PLLA molecular chains from low-energy gt conformers to high-energy gg conformers induced by extensional flow field. More interestingly, after the extrusion-stretched samples are annealed, the oriented PLLA molecular chains form oriented crystal structures such as extended-chain lamellae, common "Shish-kebabs," and hybrid Shish-kebabs, which further enhance the thermal conductivity and heat resistance of the samples. This work reveals the effects of the orientation of the matrix molecular chains and crystallites on the thermal conductivity and mechanical properties of composites and provides a new way to prepare high-performance PLLA-based composites with high thermal conductivity, excellent mechanical properties, and high heat resistance.

Thermal conductivity, morphology and mechanical properties for thermally reduced graphite oxide-filled ethylene vinylacetate copolymers

Interesting fibers researched was taken from leaves of screw pine plant of species Pandanus Odoratissimus (PO fibers). In this research, effect of alkali treatments for various soaking time and effect of fiber content on mechanical properties of unsaturated polyester matrix composites was studied. Both cross-section area and moisture absorption of individual PO fibers before and after treatment with 5% NaOH solution for various soaking times show changing. The cross section area decreases continuously, since PO fibers were treated for long time. Untreated PO fibers has the highest moisture absorption and PO fibers treated by the longest soaking times has the lowest one. PO fibers treated by longest soaking time displays the largest damage of the fiber structure. PO fiber treated by various soaking time in 5% NaOH for 90 minutes gives effect significantly on increasing tensile strength and tensile modulus of polyester composite. Effect of various PO fiber content on mechanical properties of composite was also shown in this research. Fibers content of 40% displayed maximum tensile strength of composite. From observation with scanning electron microscope (SEM), some conditions of fracture surface of the composite was obtained.

Exfoliated graphite platelets (EGPs) have attracted extensive attention owing to their exceptional combinations of thermal conductivity and mechanical properties. Mechanical exfoliation is a facile and high-throughput approach to produce single-layer or few-layer graphite platelets. Herein, octadecylamine (ODA)-grafted EGP (ODA@EGP) and subsequent polyethylene/ODA@EGP (PE/ODA@EGP) composites with different contents of ODA@EGPs were successfully prepared via ball-milling and melt-mixing methods, respectively. The thermal conductivity, crystallinity, and mechanical properties of the composites were investigated using tensile tests, the hot-wire method, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis, and thermogravimetric analysis (TGA). The results demonstrated that the thermal conductivity, mechanical properties, and thermal stability of the composites can be improved by regulating the additive contents of ODA@EGPs. When the content of ODA@EGPs was 10 wt%, the thermal conductivity of the composite reached up to 1.276 W (m-1 K-1), which is 216% higher than that of bare PE, while the tensile strength of the composite was 38.4% higher than that of PE. Additionally, thermal decomposition temperature increased by 16.2 °C. Therefore, the PE/ODA@EGP nanocomposites have great application potential in thermal management.

Discontinuous-glass-fiber-reinforced plastic (GFRP) composite material is widely used in industrial fields, mainly because glass fiber improves the strength and stiffness of polymer and because it is much less expensive than carbon fiber. It is thought that the use of long fiber is important in more efficiently improving the strength and stiffness of composites. In our previous study [1], we reported that the fracture mode of the discontinuous-fiber-reinforced composite changes from the matrix-cracking mode to the fiberbreaking mode (Fig. 1), when the aspect ratio for the fiber length to the fiber radius exceeds about 150. We also demonstrated that the strength is dramatically improved compared to the strength of the short fiber-reinforced composites and that the global load-sharing (GLS) model can roughly predict the strength (Fig. 2). Recently, Thomason [2, 3] produced the long discontinuous-fiberreinforced composites where the aspect ratio was about 250 and reported the stiffness and strength of the composites. In this article, we applied the GLS model to his experiments and discuss the validity of our models. First, we discuss the strength of unidirectional (UD) discontinuous-fiber-reinforced composites, rUD, based on the GLS assumption [4, 5]. We applied two types of GLS approaches to predict the composite strength. The GLS model focuses on one fragmented fiber (i.e., discontinuous fibers), aligned in the fiber axial direction, and neglects the interaction among fibers in the fiber cross-sectional direction. It predicts the composite’s strength by simulating the fiber damage evolution in such a fiber. One approach is based on Monte Carlo simulation [6] for fragmentation in a fiber in the composites. The other is based on the analytical model by Duva et al. [5]. (Hereafter, we refer to this as the DCW model.) Monte Carlo simulation deals with a detailed fiber stress distribution and fragment distribution, though multiple calculations are required for the prediction because it is a probabilistic approach. In contrast, the DCW model assumes an approximate stress distribution and fragment distribution, but it predicts the composite strength analytically. In simulating the fiber-damage evolution, the first approach utilized Monte Carlo simulation with the elastic– plastic hardening shear-lag model given by Okabe and Takeda [7]. The schematic of the elastic–plastic shear-lag model is illustrated in Fig. 3. The axial length of the model was set to 25 9 lf (lf is the length of discontinuous fiber), and the axial length was divided into 10,000 segments. The fiber ends in discontinuous-fiber-reinforced composites were represented by setting some random segments to the initially broken segments. Thus, the averaged length lf of the discontinuous fibers was related to the density of the initially broken segments introduced in the model. The transverse length of the matrix shear region in the model

In this work, we reported a synergistic effect of boron nitride (BN) with graphene nanosheets on the enhancement of thermal conductive and mechanical properties of polymeric composites. Here, few layered BN (s-BN) and graphene (s-GH) were used and obtained by liquid exfoliation method. The polystyrene (PS) and polyamide 6 (PA) composites were obtained via solution blending method and subsequently hot-pressing. The experimental results suggested that the thermal conductivity (TC) of the PS and PA composites increases with additional introduction of s-BN. For example, compared with the composites containing 20 wt % s-GH, additional introduction of only 1.5 wt % s-BN could increase the TC up to 38 and 34% in polystyrene (PS) and polyamide 6 (PA) matrix, respectively. Meanwhile, the mechanical properties of the composites were synchronously enhanced. It was found that s-BN filled in the interspaces of s-GH sheets and formed s-BN/s-GH stacked structure, which were helpful for the synchronously improving TC and mechanical properties of the polymeric materials.

The mechanical performance of short randomly oriented banana and sisal hybrid fiber reinforced polyester composites was investigated with reference to the relative volume fraction of the two fibers at a constant total fiber loading of 0.40 volume fraction (Vf), keeping banana as the skin material and sisal as the core material. A positive hybrid effect is observed in the flexural strength and flexural modulus of the hybrid composites. The tensile strength of the composites showed a positive hybrid effect when the relative volume fraction of the two fibers was varied, and maximum tensile strength was found to be in the hybrid composite having a ratio of banana and sisal 4 : 1. The impact strength of the composites was increased with increasing volume fraction of sisal. However, a negative hybrid effect is observed when the impact strength of the composites is considered. Keeping the relative volume fraction of the two fibers constant, that is, banana : sisal = 0.32 : 0.08 (i.e., 4 : 1), the fiber loading was optimized and different layering patterns were investigated. The impact strength of the composites was increased with fiber loading. Tensile and flexural properties were found to be better at 0.40 Vf. In the case of different layering patterns, the highest flexural strength was observed for the bilayer composites. Compared to other composites, the tensile properties were slightly higher for the composite having banana as the skin material and sisal as the core material. Scanning electron micrographs of the tensile and impact fracture surfaces of the hybrid composites having volume fraction 0.20 and 0.40 Vf were studied. The experimental tensile strength and tensile modulus of hybrid composites were compared with those of theoretical predictions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1699–1709, 2005

The mechanical and electrical properties of polymer composites often degrade due to environmental factors and shorten their service life. This article presents the effect of high temperatures on the mechanical and electrical characteristics of glass fiber reinforced composites and from the measurements, an attempt is made to predict the service life. Electrical conductivity, impedance and resistance are studied with a short-term temperature effect at 30, 60, 120, and 180 °C. The effect of temperature exposure at 120 and 160 °C for 1000, 2000, and 3000 h has been investigated to assess the changes in flexural, compressive, and tensile properties and for prediction of service life. Morphological studies are carried out to support some of the experimental results. The mechanical properties of composites are observed to deteriorate with the duration of aging. Flexural, tensile, and compressive strengths reveal a reduction of 8, 10, and 9%, after aging at 3000 h at 160 °C. The tensile strength and tensile modulus at 120 °C aged for 3000 h exhibit minimal changes as compared to unaged composites. However, with an increase in temperature to 160 °C, there is a reduction in tensile strength and modulus of composites by less than 10%, and 6% compared to composites with nanofillers. The variations in compression strength at 120 and 160 °C is not significant. Based on the reduction of tensile strength with temperature, the service life of composites has been estimated. For a predicted service life of 20 years, composites with nanofillers would be able to retain tensile strength of 90% of tensile strength.

The improved mechanical properties of Al matrix composites reinforced with oriented β-Si3N4 whisker

Thermal conductivity and mechanical properties of boron nitride (BN)-filled epoxy composite as a function of filler content, mixing conditions, and BN agglomerate size were studied. Both thermal conductivity and mechanical properties of the composite were found to increase with increases in filler content, mixing speed, mixing time, and mixing temperature, but with decrease in BN agglomerate size. Sonication was found to be more effective in decreasing the BN agglomerate size than mechanical mixing. Viscosity of the BN—epoxy mixture was also studied under various mixing and sonicating conditions. A maximum thermal conductivity of 1.97 W/mK was obtained at 28 vol.% filler content and the mixing conditions of 80 rpm, 30 min, followed by sonication.