S. Zainuddin

Improving Ballistic Performance of Polyurethane Foam by Nanoparticle Reinforcement

We report improving ballistic performance of polyurethane foam by reinforcing it with nanoscale particles. Particles were dispersed through a sonic cavitation process and the loading of particles was 3 wt% of the total polymer. Once foams were reinforced, sandwich panels were made and impacted with fragment simulating projectiles (FSPs) in a 1.5-inch gas gun. Projectile speed was set up to have complete penetration of the target in each experiment. Test results have indicated that sandwich with nanophased cores absorbed about 20% more kinetic energy than their neat counterpart. The corresponding increase in ballistic limit was around 12% over the neat control samples. The penetration phenomenon was also monitored using a high-speed camera. Analyses of digital images showed that FSP remained inside the nanophased sandwich for about 7 microseconds longer than that of a neat sandwich demonstrating improved energy absorption capability of the nanoparticle reinforced core. Failure modes for energy absorption have been investigated through a microscope and high-speed images.

Processing and characterization of epoxy nanocomposites with Mwcnt's/Cnf's using thinky and 3-roll shear mixing techniques

In this work, thinky mixing method was used to disperse multi-walled carbon nanotubes (MWCNTs) and carbon nanofibers (CNFs) in SC-1 epoxy either in isolation or in combination with 3-roll shear mixing. To achieve better dispersion, MWCNT mixing with SC-1 resin directly or pre-mixed with a solvent and then mixed with SC-1 resin after evaporating the solvent. Dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), flexural tests, electrical conductivity tests and micrographic analysis were performed on neat, 0.2 and 0.4wt% MWCNT/CNF infused SC-1 epoxy to observe the loading effect on thermo-mechanical properties of composites. DMA results indicated improvement on storage modulus and glass transition temperature, Tg, while flexural results exhibited enhanced flexural strength and modulus with up to 0.4wt% MWCNT/CNF infused epoxy resin over neat. TGA results revealed improved residue content but almost constant decomposition temperature for nanophased resin compared to neat. However, these enhancements were observed only up to 0.2 wt. % loading after which the properties were seen to either reduce or not significantly improve. These results indicate that the methods used for dispersion is suitable for low weight percent loading only.

Enhanced tensile performance of epoxy and E-glass/epoxy composites by randomly-oriented amino-functionalized MWCNTs at low contents

Effect of amino-functionalized multi-walled carbon nanotubes (NH2-MWCNTs) on the tensile performance of epoxy and E-glass/epoxy composites was investigated. Low weight percentages (0.3 and 0.4 wt%) of NH2-MWCNTs were dispersed into a DGEBA epoxy resin using combination of sonication and three-roll milling methods. Composites with plain weave E-glass fabrics were fabricated by compression molding process. Tensile test results showed a significant enhancement in strength, modulus and toughness of epoxy and E-glass/epoxy composites at 0.3 wt% loading of NH2-MWCNTs. Micrographs of NH2-MWCNTs-incorporated epoxy and E-glass/epoxy composites revealed better dispersion of nanotubes in epoxy, better bonding between nanotubes and polymer and improved interfacial adhesion between fiber/matrix at 0.3 wt% loading. Micromechanical models were used to predict the tensile properties and compared with the experimental results. An improved dispersion and hence an enhanced crosslink interaction between NH2-MWCNTs and epoxy lead to the improvements in the tensile properties of the epoxy nanocomposites close to predicted values at 0.3 wt% loading. A similar rationale applies for the increase in properties of E-glass/epoxy nanocomposites.

Effects of ultraviolet radiation and condensation on static and dynamic compression behavior of neat and nanoclay infused epoxy/ glass composites

Effects of ultraviolet radiation and condensation on the static and dynamic compressive properties of composites with and without nanoclay were investigated. Specimens were exposed to ultraviolet radiation (UV), and alternate ultraviolet radiation and condensation (UC) conditions for 5, 10, and 15 days, respectively. Compression test results showed an increase in strength and modulus with increase in strain rate and nanoclay weight percent loading. However, properties degraded upon conditioning with nanoclay infused systems showing less degradation. Scanning electron micrographs of fractured samples show better interfacial bonding in nanoclay infused composites in 2 wt. % system showing best properties.

Enhancing fatigue performance of sandwich composites with nanophased core

We report fatigue performance of sandwich composites with nanophased core under shear load. Nanophased core was made from polyurethane foam dispersed with carbon nanofiber (CNF). CNFs were dispersed into part-A of liquid polyurethane through a sonication process and the loading of nanoparticles was 1.0 wt%. After dispersion, part-A was mixed with part-B, cast into a mold, and allowed to cure. Nanophased foamwas then used to fabricate sandwich composites. Static shear tests revealed that strength and modulus of nanophased foams were 33% and 19% higher than those of unreinforced (neat) foams. Next, shear fatigue tests were conducted at a frequency of 3 Hz and stress ratio (R) of 0.1. S-N curves were generated and fatigue performances were compared. Number of cycles to failure for nanophased sandwich was significantly higher than that of the neat ones. For example, at 57% of ultimate shear strength, nanophased sandwich would survive 400,000 cycles more than its neat counterpart. SEM micrographs indicated stronger cell structures with nanophased foams. These stronger cells strengthened the sub-interface zones underneath the actual core-skin interface. High toughness of the sub-interface layer delayed initiation of fatigue cracks and thereby increased the fatigue life of nanophased sandwich composites.

A study of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) biofilms’ thermal and biodegradable properties reinforced with halloysite nanotubes:

The aim of this study is to investigate and optimize the performance of a promising biopolymer, poly (3-hydroxybutyrate-co-3-hydroxyvalerate) which can potentially replace non-biodegradable synthetic polymers derived from toxic petroleum products. Poly (3-hydroxybutyrate-co-3-hydroxyvalerate) biofilms were prepared using solvent casting method, and its thermal properties were determined using thermogravimetric and differential scanning calorimetry techniques. Also, the durability and biodegradability of these films were studied by keeping the samples in water and Alabama soil conditions for various lengths of time. Our results showed that the thermal and moisture resistance of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) biopolymer can be enhanced significantly with the addition of low halloysite nanotubes concentrations. Also, the biodegradation process of the poly (3-hydroxybutyrate-co-3-hydroxyvalerate) films was faster with the addition of halloysite nanotubes attributed to the accelerated microbial microorganism reaction in the soil. This study led to cognize that the PHBV biopolymers added with halloysite nanotubes can be successfully used for various biomedical, industrial and structural applications, and then decompose at a desired faster rate afterward.

Thermoset resin sandwich structures

Abstract In this study, the impact performance of sandwich composites fabricated using nanophased foam cores and thermoset epoxy–nanoclay reinforced face sheets was investigated. First, nanophased foam cores were prepared by adding 0.5–1% Nanocor® I-28E nanoclay in liquid polyurethane. Sandwich panels were then fabricated using these foam cores and 1–2% by nanoclay added SC-15 epoxy reinforced plain weave carbon fabric face sheets. In addition, neat sandwich panels (without nanoclay) were also fabricated for baseline comparison. The specimens cut from these panels were subjected to low-velocity impact loading and their response was recorded and compared in terms of peak load, absorbed energy, time, and deflection at peak load. The tested samples were then sectioned into two halves and failure pattern was investigated using scanning and microscopic techniques. Nanophased sandwich composites samples sustained higher loads and had lower damage areas in comparison to neat counterparts. Also, the nanophased foam cores exhibited brittle fracture.

Properties of Polyhydroxy Butyrate Polyvalerate Biopolymeric Nanocomposites Reinforced with Natural Halloysite Nanotubes

In this study, the properties of bacterial fermentation based poly(hydroxybutyrate-co-hydroxyvalerate) –PHBV thermoplastic biopolymer was investigated by reinforcing natural halloysite nanotubes (HNTs). At first, HNTs were added to PHBV polymer by melt processing technique. The modified PHBV resin was then used to fabricate films using compression molding process. X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and tensile tests were performed. XRD results showed mixed intercalated and exfoliated behavior of HNTs in PHBV matrix with an increase in interplanar spacing and decrease in peak intensity. DSC analysis showed that the crystallinity of PHBV resin increased with the increase in HNTs concentration. Also, the DSC endotherm curve showed dual melting peaks indicating formation of different crystalline phases. Higher melting and recrystallization temperature was found in nanophased samples in comparison to the pure PHBV counterpart. The thermal stability, activation energy, tensile and viscoelastic properties of nanophased samples were also increased with an optimum at 3 wt. % HNTs loading. Scanning electron micrographs (SEM) revealed river like pattern in neat films indicating a brittle failure in contrast to rougher surfaces observed in nanophased samples.

Recovery of Low-Velocity Impact Properties of Glass Fiber Reinforced Composites Through Self-Healing Technique

In this study, we report the self-healing of e-glass/epoxy composites achieved through embedding self-healing agents (SHA) filled hollow glass fibers (HGFs). At first, catalytic technique was used to fill bonded HGFs with SHA. The HGFs were then laid on e-glass fibers and the laminates were fabricated using vacuum assisted resin molding (VARIM) technique. Low-velocity impact tests at two different energy levels were conducted multiple times in the closest proximity to determine the healing efficiency. Optical microscopic study was done to see the changes in the SHA filled HGFs samples before and after impact. Results showed significant recovery of impact properties with 4.47% lost in peak load after second impact in SHA samples whereas it was 27.7% in control samples. The loss in energy to peak load was 20.44% in SHA filled samples, whereas 41% in control samples. Optical microscopy images showed filling of cracks produced after impact with SHA reflecting the significant recovery of impact properties.Copyright

Effects of Ultraviolet Radiation and Condensation on Static and Dynamic Compressive Behavior of Nanophased Glass/Epoxy Composites

Increased use of fiber reinforced polymeric composites in an outdoor environment has led to questions concerning their environmental durability, particularly as related to ultraviolet (UV) radiation, moisture, and temperature exposure. This chapter describes the effects of UV and UV radiation + condensation (UC) on the static and dynamic compressive properties of unidirectional glass/epoxy composites. The samples were manufactured using an infusion process with and without nanophased epoxy and exposed to UV radiation and UC conditioning for 5, 10, and 15 days respectively. Nanophased epoxy was prepared with 1 wt%and 2 wt% nanoclay. Static compression tests were carried out using MTS test system under displacement control mode at a crosshead speed of 1.27 mm/min. Dynamic compression tests were carried out using modified Split Hopkinson Pressure Bar (SHPB) at different strain rates. The compressive strength and stiffness were evaluated as functions of strain rate. Results of the study showed that samples lost weight when exposed to UV radiation, whereas they gained weight when exposed to UC conditioning. Weight gain or loss was lower for nanophased composites when compared to neat samples. Static and high strain compressive properties reduced for all the nanophased samples when compared with room temperature samples. However, the loss in compressive properties was lowest in nanophased composites with 2 wt% nanoclay.