All issues / Volume 15 (2021) / Issue 3 (March)
This is an editorial article. It has no abstract.
The effect of crack propagation management by using a fused deposition modeling (FDM) technique on the environmental stress cracking (ESC) behavior of neat polycarbonate (PC) and PC with 1 vol% SiO2 nanocomposites were investigated. The results demonstrate that the crack growth behavior of materials and their ESC resistance are strongly dependent on the printing direction. The ESC resistance and failure time of an FDM print-on injection-molded specimen exhibit the greatest values when the printing direction parallels to the load direction. Comparative analyses of the fracture surfaces reveal that the excellent stress cracking resistance can contribute to favorable stress and load distribution at the crack front area, where the printed continuous strands in alignment with the load can efficiently carry and transfer it. However, the degree of ESC improvement by managing the direction of craze/crack propagation via printing direction is more pronounced in neat PC than those of PC-SiO2 nanocomposites.
In this work, the mechanical and fracture performance of epoxy nanocomposites consisting of epoxide and imidazole functionalized silica nanoparticles has been studied. The post-synthesis grafting method was utilized to functionalized SiO2 nanoparticles with GPTMS (GGS) and used them as reinforcement (0–2 wt%) in epoxy resin. The cure behavior of nanocomposites demonstrated that the composite has excellent cure capability at 0.5 wt% of GGS. The composite containing 0.5 wt% of GGS exhibited significant improvement in tensile strength (~65 %) and modulus of toughness (~272 %), respectively. Additionally, the flexural strength, flexural modulus, and work of flexural were enhanced by ~48, ~50, and ~48%, respectively. Interestingly, the GGS showed its tremendous potential to improve the fracture toughness (K1C) and the fracture energy (G1C) of the nanocomposite by ~97 and ~292 %, which is also evident by the study of cure behavior. The fractography analysis endorsed the enhancement of material properties due to the use of GGS in the epoxy matrix. Failure investigation examined under FESEM elucidated forced the crack to move around the poles of the nanoparticles due to better interfacial adhesion. Hence, GGS nanoparticle has the potential to use as an excellent cost-effective reinforcement for the epoxy matrix to mitigate the brittle failure in epoxy composites.
Polymer composites were manufactured using biocarbon particles as a reinforcing filler to improve the mechanical and thermal properties. However, a detailed examination of dispersion and agglomeration of filler is essential to correlate the filler/matrix and the filler/filler interactions with the mechanical properties of the product. We investigated the variations of mechanical, agglomeration behavior of fillers, and thermal properties of polypropylene (PP)/coconut shell biocarbon (CSB) composites. PP/CSB composites were prepared by melt mixing process varying the CSB content (0 to 20 wt%) using a Brabender mixer. The nanomechanical mapping of the composites studied using Atomic Force Microscopy revealed an increase in Young’s modulus from 1.6 to 2.9 GPa when CSB loading increased from 0 to 20 wt%. The dispersion and agglomeration of CSB filler in the PP matrix were investigated using 3D reconstructed images with the help of X-ray micro-CT, and a dedicated 3D reconstruction software. The thermal stability of the PP/CSB composites also improved with an increase in CSB content in PP.
This study aims to investigate the effect of different carbonaceous fillers, carbon black (CB) biocarbon (BC), and a hybrid filler of both (BC-CB), in a natural rubber matrix. It was found that the addition of hybrid filler based on a sustainable biocarbon (BC) and carbon black (CB) revealed a significant effect on reducing the rolling resistance properties. Dried distillers’ grain with solubles (DDGS), a co-product from corn ethanol industry pyrolyzed at 900 °C, was used to produce the biocarbon. As compared to the carbon black, the particle size of the biocarbon was larger which was reflected in the tensile strength of the biocarbon composites. This observation was correlated using swelling studies and found to be proportional to their crosslink density. The thermal characterizations showed similar transitions and degradation mechanisms in all the composites, which confirmed a comparatively similar behavior of BC with CB. Moreover, these findings justify further tuning of biocarbon into nanosize and this could expand the scope in the utilization of this sustainable filler for the fabrication of various rubber products such as tires and hoses, etc.
The study scrutinizes the coincidental formation and stabilization of bio-based polyamide (PA) nanofibers within biodegradable polylactide (PLA) in a single stage. The results reveal that the formation of nanofibril-matrix morphology is dominated by viscosity and elasticity ratios of the dispersed component to the matrix. It is shown that there are upper and lower bounds for the ratios providing efficient in situ fibrils formation. For PLA/PA, critical values of viscosity and elasticity ratios are in the range of 0.3–2.8 and 2.0–15.0, respectively. As these parameters decrease, thinner and longer PA nanofibers form, and ultimately a network of nanofibrils develops. Below the lower boundary, formed very thin, less than 250 nm, nano - fibrils become unstable, and their flow is accompanied by breaking-up into sub-nanodroplets. Above the upper boundary, the viscosity of the polymer matrix is insufficient to arrange droplets to fibers transitions, and the presence of a compatibilizer can only lead to a partial formation of a fibrillar structure. The shear-induced crystallization is proposed for the stabilization of PA nanofibers immediately under applying a high shear rate without subsequent cooling. A higher effect (more significant increase in the crystallization temperature of PA and a narrower temperature range in which the crystallization process occurs) is achieved in the case of PA with a higher viscosity.
A nanostructuring approach was applied to epoxy/carbon fiber (CF) composite laminates to establish a short transport path between the CF of the adjacent laminates. This involved the utilization of carboxylic-plasma-functionalized multiwalled carbon nanotube (COOH-MWCNT) and carboxylic-plasma-functionalized graphene nanoplatelet (COOH-GNP) hybrids filled epoxy resin at various nanofiller hybrid ratios and concentrations. Novel Raman spectroscopy imaging and surface potential atomic force microscopy (AFM) mapping were employed to analyze the state of nanofiller dispersion on the laminate surfaces. The mixture of COOH-GNPs and COOH-MWCNTs in a ratio of 50:50 wt% at 4 phr was identified to synergetically improve their dispersion and the laminate electrical and mechanical properties. It offered optimal segregation of nanofiller hybrids. At this composition, the maximum electrical conductivity and the highest flexural strength were achieved in the composite laminate, which were approximately 75 S/cm and 675 MPa, respectively.
The article presents a detailed study of the curing process of liquid crystalline epoxy resin focused on selecting optimal crosslinking conditions allowing to achieve a highly anisotropic product. By the manipulation of time, temperature, and applied magnetic induction during the chemical reaction, leading to the formation of neat epoxy and carbon-epoxy composite, the desired conclusions were developed. During X-ray analysis, it was established that the most anisotropic network is created when the following parameters are chosen: low curing temperature, short time of curing, and high magnetic induction. These conditions, however, do not allow to synthesize fully cured products, so the two-stage process was proposed, which slightly deteriorates the level of anisotropy, giving maximum conversion in return. The level of order is described with a dependent on the intensity of peaks present on the X-ray scattering plots parameter called the orientation function OF. The introduction of a graphite-like nanofiller generally slightly decreases the anisotropy of the polymer network. The main finding of this article is the optimized process of curing, allowing to obtain highly anisotropic material. This optimization shows tendencies between material ordering and curing properties, so it can be useful in future studies allowing to reach optimal conditions a lot faster.