Rheological behavior of cycloolefin copolymer/graphite composites

More than just a beer - Brewers' spent grain, spent hops, and spent yeast as potential functional fillers for polymer composites

Beer is among the most popular beverages in the world, with the production distributed uniformly between the biggest continents, so the utilization of brewing by-products is essential on a global scale. Among their potential recipients, the plastics industry offers extensive range of potential products. Herein, the presented study investigated the application of currently underutilized solid brewing by-products (brewers' spent grain, spent hops, spent yeast) as fillers for highly-filled poly(ε-caprolactone)-based composites, providing the first direct connection between spent hops or spent yeast and the polymer composites. Comprehensive by-product characterization revealed differences in chemical composition. The elemental C:O ratio, protein content, and Trolox equivalent antioxidant capacity varied from 1.40 to 1.89, 12.9 to 32.4 wt%, and 2.41 to 10.24 mg/g, respectively, which was mirrored in the composites' structure and performance. Morphological analysis pointed to the composition-driven hydrophilicity gap limiting interfacial adhesion for high shares of brewers' spent grain and spent hops, due to high hydrophilicity induced by carbohydrate content. Phytochemicals and other components of applied by-products stimulated composites' oxidative resistance, shifting oxidation onset temperature from 261 °C for matrix over 360 °C for high spent yeast shares. Simultaneously, spent yeast also provided compatibilizing effects for poly(ε-caprolactone)-based composites, reducing complex viscosity compared to other fillers and indicating its highest affinity to poly(ε-caprolactone)due to the lowest hydrophilicity gap. The presented results indicate that the proper selection of brewing by-products and adjustment of their shares creates an exciting possibility of engineering composites' structure and performance, which can be transferred to other polymers differing with hydrophilicity.

Improving Thermal Conductivity of Injection Molded Polycarbonate/Boron Nitride Composites by Incorporating Spherical Alumina Particles: The Influence of Alumina Particle Size

In this work, the influences of alumina (Al₂O₃) particle size and loading concentration on the properties of injection molded polycarbonate (PC)/boron nitride (BN)/Al₂O₃ composites were systematically studied. Results indicated that both in-plane and through-plane thermal conductivity of the ternary composites were significantly improved with the addition of spherical Al₂O₃ particles. In addition, the thermal conductivity of polymer composites increased significantly with increasing Al₂O₃ concentration and particle size, which were related to the following factors: (1) the presence of spherical Al₂O₃ particles altered the orientation state of flaky BN fillers that were in close proximity to Al₂O₃ particles (as confirmed by SEM observations and XRD analysis), which was believed crucial to improving the through-plane thermal conductivity of injection molded samples; (2) the presence of Al₂O₃ particles increased the filler packing density by bridging the uniformly distributed BN fillers within PC substrate, thereby leading to a significant enhancement of thermal conductivity. The in-plane and through-plane thermal conductivity of PC/50 μm-Al₂O₃ 40 wt%/BN 20 wt% composites reached as high as 2.95 and 1.78 W/mK, which were 1183% and 710% higher than those of pure PC, respectively. The prepared polymer composites exhibited reasonable mechanical performance, and excellent electrical insulation properties and processability, which showed potential applications in advanced engineering fields that require both thermal conduction and electrical insulation properties.

Gas Barrier, Thermal, Mechanical and Rheological Properties of Highly Aligned Graphene-LDPE Nanocomposites

This contribution reports on properties of low-density polyethylene-based composites filled with different amounts of graphene nanoplatelets. The studied samples were prepared in the form of films by means of the precoating technique and single screw melt-extrusion, which yields a highly ordered arrangement of graphene flakes and results in a strong anisotropy of composites morphology. The performed tests of gas permeability reveal a drastic decrease of this property with increasing filler content. A clear correlation is found between permeability and free volume fraction in the material, the latter evaluated by means of positron annihilation spectroscopy. A strong anisotropy of the thermal conductivity is also achieved and the thermal conductivity along the extrusion direction for samples filled with 7.5 wt % of GnP (graphene nanoplatelets) reached 2.2 W/m·K. At the same time, when measured through a plane, a slight decrease of thermal conductivity is found. The use of GnP filler leads also to improvements of mechanical properties. The increase of Young's modulus and tensile strength are reached as the composites become more brittle.

Improved thermal and mechanical properties of carbon fiber filled polyamide 46 composites

The thermal and mechanical properties of polyamide 46 (PA46) filled with carbon fiber (CF/PA46) composites were studied. CF/PA46 was fabricated by the method of melt blending and injection molding. The results showed that thermal conductivity, tensile strength and impact strength of the composite increased with the increase of weight fraction of CF, however, the elongation at the break decreased as its weight fraction increased. The addition of CF had little effect on the melting temperature of composites, while the crystallization onset (To) and crystallization peak (Tp) temperatures of composites shifted to higher points. The scanning electron microscope images showed that when the weight fraction of CF was increased, the CF was more likely to form thermal chains and a network. When the CF weight fraction was 40%, thermal conductivity was 1.49 W/(m·K), approximately 5.54 times as high as that of the pure PA46, and the thermal diffusivity was 0.9755 mm2/s, 6.5 times higher than that of the pure matrix. Comparing the experimental data with the three expected thermal conduction models data, the Maxwell-Eucken thermal conduction model was considered more suitable for the PA46/CF composite, in which the weight fraction of the filler was <10% in the thermal conductive system.

Highly electrically conducting poly(L-lactic acid)/graphite composites prepared via in situ expansion and subsequent reduction of graphite

In this paper, highly electrically conductive polymeric composites were obtained by low-temperature expandable graphite (LTEG) filling poly(L-lactic acid) (PLLA) in the presence of ascorbic acid via an in situ exfoliation and subsequent reduction process during the melt blending. The electrical conductivity of the PLLA/reduced and expanded graphite (R-EG) composites was determined by a four-point probe resistivity determiner and compared with that of the PLLA/expanded graphite (EG) composites. The percolation threshold of PLLA/R-EG blends decreased from 11.2 wt% to 7.1 wt%, which illustrated the superiority of R-EG to the electrically conducting ability of PLLA composites. At the graphite concentration near the percolation threshold, the electrical conductivity of PLLA/R-EG composites was much higher than that of PLLA/EG composites. The effective in situ expansion and reduction of LTEG were crucial to the overall electrical conductivity of the blends, which was confirmed by Fourier transform infrared (FTIR) and X-ray diffraction (XRD) analysis. Dynamic rheology analysis confirmed that the connected networks that were the major cause of the rapid increase in electrical conductivity were much more easily formed for PLLA/R-EG blends than those of PLLA/EG blends. Thermogravimetric analysis (TGA) was applied to determine the decomposition and thermal stability of the PLLA/R-EG composites.

Enhancement in thermal conductivity and mechanical properties via large-scale fabrication of boron nitride nanosheets

In this study, a facial method of fabricating hexagonal boron nitride nanosheet (BNNS) was proposed. Isopropyl alcohol was employed as the solvent to obtain the BNNS via exfoliation of the pristine hexagonal boron nitride. The yield of the exfoliated BNNS with thickness less than 20 nm was as high as 0.17–0.2 mg mL−1. The BN- and BNNS-filled polyamide 6 (PA6) composites were subsequently prepared by melt blending, and a comparison of thermal conductivity and mechanical properties of the resultant composites were demonstrated. Results indicated that the PA6/BNNS composites showed superior mechanical and thermal conductive properties when compared with that of neat PA6 and PA6/BN composites. At a filler-loading fraction of 40 wt%, thermal conductivity of the PA6/BNNS composite reached 2.496 W mK−1, which was 21.8% higher than that of PA6/BN composites at the same filler-loading concentration. In addition, the tensile strength of PA6/BNNS composites was invariably higher than that of neat PA6, with a 6.23% increment at a filler concentration of 30 wt%. Based on the results of differential scanning calorimetry, a new crystallization peak ( TCC, 2) was observed at higher temperature region for the filler-containing composites and the position of the new peak gradually shifted to higher temperatures with an incremental loading concentration of BN and BNNS.