Unfilled Counterparts Research Articles

Carbon Fiber–Bismaleimide Composites Filled with Nickel‐Coated Single‐Walled Carbon Nanotubes for Lightning‐Strike Protection

AbstractMultifunctional carbon fiber composites are imperative for next‐generation lightweight aircraft structures. However, lightning‐strike protection is a feature that is lacking in many modern carbon fiber high‐temperature polymer systems, due to their high electrical resistivity. This work presents a study on processing, materials optimization, and property development of high‐temperature bismaleimide (BMI)–carbon fiber composites filled with nickel‐coated single‐walled carbon nanotubes (Ni‐SWNTs) based on three key factors: i) dispersion of Ni‐SWNTs, ii) their surface coverage on the carbon plies and, iii) the composite surface resistivity. Atomic force microscopy analysis revealed that coating purified SWNTs with nickel enabled improved dispersion which resulted in uniform surface coverage on the carbon plies. The electrical resistivity of the baseline composite system was reduced by ten orders of magnitude by the addition of 4 wt% Ni‐SWNTs (calculated with respect to the weight of a single carbon ply). Ni‐SWNT–filled composites showed a reduced amount of damage to simulated lightning strike compared to their unfilled counterparts, as indicated by the minimal carbon fiber pull‐out.

The effects of different silane crosslinking approaches on composites of polyethylene blends and wood flour

AbstractThough silane chemistry has been used to crosslink unfilled polyethylene for many years, such crosslinking has only been recently applied to wood plastic composites to improve properties such as creep resistance. However, the presence of wood significantly changes the silane chemistry and a greater understanding is necessary for optimal processing and performance. We investigated three different approaches of adding silane and peroxide during reactive extrusion of wood‐plastic composites were investigated and compared to their unfilled counterparts. Up to 2 grams of a 20:1 solution of vinyltrimethoxysilane and dicumyl peroxide by weight were added per 100 grams of plastic. Low density polyethylene, high density polyethylene, and a blend of the two were investigated as matrices in composites containing approximately 25% wood flour. The unfilled plastics crosslinked efficiently and little premature crosslinking occurred during processing. Though only modest improvements in tensile strengths were found in unfilled plastics, the notched Izod impact energy of unfilled HDPE improved nearly 600% when crosslinked. Unlike the unfilled plastics, most of the crosslinking of the composites occurred during processing. This resulted in high viscosities and processing difficulties, negating some of the advantages of a separate crosslinking step and limiting the amount of crosslinking possible. Some reinforcement of the plastics by the wood flour was achieved when sufficient crosslinking solution was added. Adding crosslinking solution also and greatly increased reverse‐notched impact energies. The differences between the approaches for preparing the crosslinked composites appeared to largely be a matter of efficiency in terms of the amount of crosslinking solution required to affect processing and performance. The most efficient approach was a two‐step procedure where the silane was first grafted to the plastic and then wood flour was compounded with the grafted silane in a second step. Published 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Microcellular Foaming of Layered Double Hydroxide−Polymer Nanocomposites

Microcellular foams of polystyrene (PS), poly(styrene-co-acrylonitrile) (SAN), and poly(methyl methacrylate) (PMMA) having organically modified layered double hydroxides (LDH) were prepared using a high-pressure CO2 dissolution foaming process and characterized both structurally and thermo-mechanically. The saturation concentration of CO2 was found to increase with the incorporation of LDH nanoparticles into the PMMA, while the opposite effect was observed in the PS and SAN nanocomposites with respect to the pure polymers. The CO2 desorption diffusion coefficient substantially decreased in the nanocomposites comparatively to the respective pure polymers. The incorporation of hydrotalcite (HT) into the polymers and subsequent foaming resulted in foams with finer and more isotropic cellular structures, related to a cell nucleation effect promoted by the particles. No significant differences were found among the several foamed nanocomposites. Both PS and SAN nanocomposite foams displayed higher glass transition temperatures than the respective unfilled ones, related to a higher amount of residual CO2 in the last, favoring plasticization. The contrary effect was observed in PMMA, attributed to a combined plasticizing effect promoted by the higher affinity of PMMA for CO2 and greater interaction with the organically modified HT platelets. Although no significant differences were found among the several nanocomposite foams and respective unfilled counterparts, the incorporation of HT limited the reduction observed in the specific storage moduli with foaming, related to a finer cellular structure induced by the HT particles.

Thermoplastic Composites Based on Renewable Natural Resources: Unplasticized PVC/Olive Husk

The current study explores the potential of eco-friendly biomaterials, namely olive husk (OH) as a reinforcing filler for PVC composite. Thus, composite-based unplasticized poly(vinyl chloride) (u PVC) and olive husk were mixed by a Brabender two-roll mill at 180°C and 25 rpm. The olive husk concentration was progressively varied from 0–20 phr. The fabricated samples were inspected with respect to their tensile properties, impact strength, thermal stability, and density and water uptake. It has been found that stress at peak increased with filler loading up to certain loading. This scenario was related to hydrogen bond formation due to polar-polar interactions. Evidence of the hydrogen bond formation between the polymer matrix and the olive husk was examined with the aid of attenuated reflectance infrared spectra (ATR-IR). Such interactions were cited to justify the improved performance of the composites. Fracture mode and filler dispersion of the composites were compared to the unfilled counterpart by scanning electron microscopy (SEM). The influence of olive husk on the thermal stability of the PVC composites was studied by differential scanning calorimeter (DSC). It has been found that the enthalpy of fusion was improved with OH loading. The observed trend was correlated with the phenolic hydroxyl group of the lignin component used as an antioxidant.

Deuterium NMR study of the microscopic deformation and chain dynamics of polybutadiene networks

2H NMR measurements on carbon-black-filled&crosslinked polybutadiene (PB) networks and unfilled counterpart reveal the strong uniaxial-elongation dependence of both the transverse relaxation rate (1/T 2) and the splitting distance (Δν) of NMR lineshape; furthermore, the fluctuating part, instead of the static residual part, of quadrupolar interaction is found to govern the transverse relaxation signal at large deformation ratios (e.g., λ extt1.5) or high filler loads (e.g., 25phr or higher). The comparison of the T 2's or Δν's in both unfilled and filled cases and in the cases of different λ ext's indicates that in filled cases, the rubber matrix does not undergo overstrain in a wide range of λ ext, and chain breakage is prevented. This is also supported by the environmental scanning electron microscopy evidence for the deformation of carbon black clusters/network. In contrast, the unfilled PB network tends to undergo inhomogeneous deformation as λ ext increases, as confirmed by more than one 2H NMR doublets.

Use of porcine renal capsule matrix as a full-thickness dermal wound-healing material in rats

To compare the utility of porcine renal capsule matrix (RCM) with porcine small intestinal mucosa (SIS) in a rat full-thickness skin wound model. Groups of rats had surgically-created wounds filled with either SIS or RCM. On each rat a contralateral wound was left unfilled (RCM-U or SIS-U). Wound diameter was measured 3, 7, 12, 17, 26 and 30 days after creation. Wound sites sampled 3, 7, 14, 28, 42 and 56 days after wound creation were numerically graded for degree of histologic change and for collagen content, based on intensity of trichrome staining. Wounds in all groups rapidly contracted to less than 50% of the original diameter within 12 days. There were no differences in wound diameter between RCM- and SIS-treated wounds at any time point, but these wounds had significantly greater (p < 0.001) diameters than their unfilled counterparts on days 7, 12 and 17. There were no differences in histologic scores or trichrome-staining scores between RCM- and SIS-treated wounds and their unfilled counterparts at any time point, except for a greater (p < 0.05) histologic score in SIS-treated wounds compared with unfilled controls on day 14. In both treatment groups an acute inflammatory response at the wound site was soon replaced by an influx of macrophages and fibroblasts. The results show that RCM is equivalent to SIS for the treatment of full-thickness wounds and that these materials may enhance wound healing in terms of wound-tissue collagenisation and maturation. These materials therefore merit further study in other wound-care models.