Sahrim Hj. Ahmad

Electromagnetic and absorption properties of some microwave absorbers

Electromagnetic properties of a thermoplastic natural rubber (TPNR), a lithium–nickel–zinc (Li–Ni–Zn) ferrite and a TPNR–ferrite composite subjected to transverse electromagnetic (TEM) wave propagation were investigated. The incorporation of the ferrite into the matrix of the TPNR was found to reduce the dielectric loss but the magnetic loss increased. The absorption characteristics of all the samples subjected to a normal incidence of TEM wave were investigated based on a model of a single-layered plane wave absorber backed by a perfect conductor. It is evident from a computer simulation that the ferrite is a narrowband absorber, whereas the polymeric samples show broadband absorption characteristics. Minimal reflection of the microwave power or matching condition occurs when the thickness of the absorbers approximates an odd number multiple of a quarter of the propagating wavelength. This is discussed as due to cancellation of the incident and reflected waves at the surface of the absorbers. The Li–Ni–Z...

A facile thermal-treatment route to synthesize ZnO nanosheets and effect of calcination temperature

A facile thermal-treatment route was successfully used to synthesize ZnO nanosheets. Morphological, structural, and optical properties of obtained nanoparticles at different calcination temperatures were studied using various techniques. The FTIR, XRD, EDX, SEM and TEM images confirmed the formation of ZnO nanosheets through calcination in the temperature between 500 to 650°C. The SEM images showed a morphological structure of ZnO nanosheets, which inclined to crumble at higher calcination temperatures. The XRD and FTIR spectra revealed that the samples were amorphous at 30°C but transformed into a crystalline structure during calcination process. The average particle size and degree of crystallinity increased with increasing calcination temperature. The estimated average particle sizes from TEM images were about 23 and 38 nm for the lowest and highest calcination temperature i.e. 500 and 650°C, respectively. The optical properties were determined by UV–Vis reflection spectrophotometer and showed a decrease in the band gap with increasing calcination temperature.

Reinforced thermoplastic natural rubber hybrid composites with Hibiscus cannabinus, L and short glass fiber - Part I: Processing parameters and tensile properties

Hybrid composite of thermoplastic natural rubber (TPNR) reinforced with Hibiscus cannabinus, L fiber (kenaf fiber: KF) and short glass fiber (GF) were prepared via melt blending method using internal mixer, at various temperatures, speed and time. TPNR matrix is a blend of polypropylene (PP), liquid natural rubber (LNR) and natural rubber (NR) at a ratio of 70 : 10 : 20. Processing parameters were determined from the tensile strength based on fiber content with 50: 50 ratios of GF and KF. Using the optimum processing parameters, tensile test was carried out for reinforced TPNR—KF—GF hybrid composites (0—20% by volume), with and without addition of silane coupling agent and maleic anhydride grafted polypropylene (MAPP). The result of tensile strength has shown that the increasing in kenaf fiber content substantially reduced the tensile strength and modulus. Scanning electron microscopy (SEM) has shown that the composite, with coupling agent or compatibilizer, promotes better fiber—matrix interaction.

Development of zero ODP rigid polyurethane foam from RBD palm kernel oil

In recent years, the use of renewable resources has attracted the attention of many technologists as potential substitutes for petrochemicals, mainly from forest products. Palmeri oil, vernonia oil, castor oil and recently the cardanol oil are naturally synthesized with multiple functionality and are a new source of renewable resources which have a very bright future as an alternative to petroleum feedstock [1–3]. Since the invention of polyurethane by Bayer in 1937, the utilization of polyurethane is ubiquitous. Polyurethanes are block copolymers containing blocks of low molecular weight polyesters or polyethers covalently bonded by a urethane group (-NHCO=O). These polymers are synthesized by reacting three basic components consisting of polyisocyanate, polyhydroxyl-containing polymer (i.e. polyester or polyether polyols) and a chain extender, which is usually low molecular weight diols or diamines (i.e. 1,4-butanediol or 1,4-dibutylamine) [4]. Currently, there is a wide range of polyisocyanates, polyols and chain extenders commercially available and this has led to almost unlimited possibilities for polyurethane materials. Because of the inherent versatility on polyurethane syntheses, the properties of this class of polymers can be easily engineered to suit the applications required. Palm kernel oil is the focus of this study because it is available in abundance in Asia, especially Malaysia. In addition, it is produced from the production of palm fruit as much as 3.8 tons per hectare per annum [5], as well as offering very low market price. In this study, the RBD (refined-bleached-deodorized) palm kernel oil was derivatized using a new development in polyurethane technology by combination with polyethylene glycol under basic condition. Methods used in the process involved polycondensation and transesterification [6] where low reaction temperature and short reaction time as well as high percentage of yield are offered. The RBD palm kernel oil (Lee Oilmill, Klang) together with a reagent, which was a mixture of proprietary polyhydroxyl compound and basic catalyst were reacted at ratio of 80 : 20 to get the highest functionality value possible. The reaction was carried out in laboratory scale. The mixture was continuously stirred in a 2L-glass reactor and was maintained at 183± 2 ◦C for 20–30 min, with nitrogen blanket throughout the process. The reflux flask was connected to a condenser and the vacuum pump to withdraw the water from the system. The progress of the reaction was monitored by sampling at intervals. The samples were then analyzed. At the end of the reaction, the polyol produced was kept in a sealed cap glass container for analysis. 120 g of crude MDI (Cosmonate M-200, Cosmopolyurethane, Port Klang) was poured into 100 g of the mixture of the RBD palm kernel oil polyol with additives (surfactant, catalyst and water) and was mixed thoroughly using a standard propeller with speed of 3500 rpm for 10 s. The mixture was then poured into a waxed mold, covered and screwed tight. The foam was demolded after 10 min. It was then conditioned for 16 h at 23± 2 ◦C before characterization. Foams were characterized for their apparent densities, compression strength, dimensional stability and water absorption following the standard method BS 4370: Part 1: 1988 (Rigid polyurethane foam produced by the press injection method). The RBD palm kernel oil changed from a cloudy pale yellow solid (at 24–25 ◦C) before derivatization to a clear golden yellow liquid after reaction. It has a viscosity of 262.5 mpa s and density 948.2 kg/m3 at 25 ◦C. The moisture content was 0.12% and it had a pH value of about 9–10. The cloud point was observed at 13 ◦C. The hydroxyl number calculated was approximately in the range of 350–370 mg KOH/g sample. Through gel permeation chromatography (GPC), the molecular weight was calculated at the range of 430– 450, leading to functionality value of 2.8–3.0. The purity of the synthesized polyol was checked by thin layer chromatography and was confirmed to be reproducible. Fig. 1 show the two peaks used for monitoring the derivatization process. Peak B does not appear in the FTIR spectrum of underivatized RBD palm kernel oil. The ratios of the percentage transmittance of these two peaks are calculated and plotted against the reaction temperatures.

Tensile and impact properties of thermoplastic natural rubber reinforced short glass fiber and empty fruit bunch hybrid composites

Thermoplastic natural rubber (TPNR) hybrid composite with short glass fiber (GF) and empty fruit bunch (EFB) fiber were prepared via the melt blending method using an internal mixer type Thermo Haake 600p. The TPNR were prepared from natural rubber (NR), liquid natural rubber (LNR) and polypropylene (PP) thermoplastic, with a ratio of 20:10:70. The hybrid composites were prepared at various ratios of GF/EFB with 20% volume fraction. Premixture was performed before the material was discharged into the machine. The study also focused on the effect of fiber (glass and EFB) treatment using silane and maleic anhydride grafted polypropylene (MAgPP) as a coupling agent. In general, composite that contains 10% EFB/10% glass fiber gave an optimum tensile and impact strength for treated and untreated hybrid composites. Tensile properties increase with addition of a coupling agent because of the existence of adherence as shown in the scanning electron microscopy (SEM) micrograph. Further addition of EFB exceeding 10% reduced the Youngs modulus and impact strength. However, the hardness increases with the addition of EFB fiber for the untreated composite and decreases for the treated composite.

Effect of nickel-cobalt-zinc ferrite filler on electrical and mechanical properties of thermoplastic natural rubber composites

ABSTRACT Thermoplastic natural rubber (TPNR) as polymer matrix was prepared by the melt blending method. Nickel-cobalt-zinc (NiCoZn) ferrite as a filler was prepared by the double-stage sintering method in air. The filler was incorporated in the polymer matrix using a Brabender internal mixer. The filler content was varied from 0 to 30 wt.%. The morphological study of the fractured surface using a scanning electron microscope (SEM) shows the effects of strain. The X-ray diffraction (XRD) indicates the coexistence of both the ferrite and thermoplastic. Electrical properties were studied using a high frequency response analyzer (HFRA) at room temperature (298°K). The results show that resistivity (ρ) decreases, but the dielectric constant increases, with increasing filler content. The resistivity and dielectric constant for all the composites are in the range of 8.9 × 106–9.7 × 105 Ωm and 33–72, respectively. A sharp change in both quantities around 15 wt.% filler content is interpreted as due to the transition from a dispersed system to an attached system. The tensile study shows that the elongation at break point and the tensile strength of the composite at room temperature decrease with increasing filler content. The hardness of the samples decreases with increasing filler content.

Essential Work of Fracture and Acoustic Emission Study on TPNR Composites Reinforced by Kenaf Fiber

Kenaf fiber (KF) based thermoplastic natural rubber (TPNR) composite was produced by melt blending with polypropylene (PP). Kenaf fiber (15% by volume) and TPNR were mixed in as Haake 600p internal mixer. The fracture behavior of the TPNR matrix and of TPNR—kenaf (with and without maleic anhydride grafted polypropylene, MAPP) composites was evaluated using the essential work of fracture (EWF) method and double edge notched tensile (DENT) specimens. Various ligament lengths were employed ranging from 4 to 12 mm. The strain rate was fixed at 2 mm/min. The specific work of fracture (we) and plastic work (βwp) showed the highest energy for TPNR that corresponds to its ductility and allows the application of the EWF approach. It was found that the presence of kenaf fibers and MAPP reduced the toughness of TPNR and changed the ductile fracture to brittle behavior. SEM observation revealed that energy absorption mechanisms include matrix deformation, fiber pullout, and fiber breakage. Acoustic emission (AE) was employed to analyze the failure processes further. The signals emitted by composites were substantially higher than that of the TPNR matrix, reflecting that also the failure mechanisms were affected by the fibers incorporated.

Mechanical Properties of Kenaf–Thermoplastic Natural Rubber Composites

Kenaf–thermoplastic natural rubber (Kenaf–TPNR) composites were developed and evaluated in this study. The kenaf was blended with TPNR and maleic anhydride-grafted polypropylene (MAPP) as a compatibilizer in an internal mixer (Brabender). The mechanical properties of the composites were investigated by tensile, impact, flexural, and morphologic properties by scanning electron microscope (SEM). The incorporation of the kenaf fiber into the TPNR matrix resulted in an improvement in the tensile strength and Youngs modulus. However, the maximum strain and impact strength decreased with increased filler loading. The better performance was attributed to the addition of MAPP due to improvements in the wetting of the filler surface. The addition of MAPP produced composites with improved tensile strength, Youngs modulus, and flexural stiffness. SEM was employed to investigate the fiber surface, fiber pullout, and fiber–matrix interaction of composites.

Induction of apoptosis in cancer cells by NiZn ferrite nanoparticles through mitochondrial cytochrome C release

The long-term objective of the present study was to determine the ability of NiZn ferrite nanoparticles to kill cancer cells. NiZn ferrite nanoparticle suspensions were found to have an average hydrodynamic diameter, polydispersity index, and zeta potential of 254.2 ± 29.8 nm, 0.524 ± 0.013, and −60 ± 14 mV, respectively. We showed that NiZn ferrite nanoparticles had selective toxicity towards MCF-7, HepG2, and HT29 cells, with a lesser effect on normal MCF 10A cells. The quantity of Bcl-2, Bax, p53, and cytochrome C in the cell lines mentioned above was determined by colorimetric methods in order to clarify the mechanism of action of NiZn ferrite nanoparticles in the killing of cancer cells. Our results indicate that NiZn ferrite nanoparticles promote apoptosis in cancer cells via caspase-3 and caspase-9, downregulation of Bcl-2, and upregulation of Bax and p53, with cytochrome C translocation. There was a concomitant collapse of the mitochondrial membrane potential in these cancer cells when treated with NiZn ferrite nanoparticles. This study shows that NiZn ferrite nanoparticles induce glutathione depletion in cancer cells, which results in increased production of reactive oxygen species and eventually, death of cancer cells.

Performance of rubberwood fiber-thermoplastic natural rubber composites

Rubberwood fiber–thermoplastic natural rubber (RWF–TPNR) composites were prepared and evaluated in this study. The RWFs were supplied in the form of thermomechanical pulp (TMP) from the Hume Fiberbord Company in Malaysia. The fibers were screened to 0.5–1 mm sizes and blended with TPNR and maleic anhydride–grafted polypropylene (MAPP) as a compatibilizer in the internal mixer of Brabender Plasticorder machine. The mechanical, thermal properties and morphology of the composites were investigated by tensile, impact, flexural, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and scanning electron microscope (SEM). The results showed that the tensile strength and Youngs modulus increased, while tensile strain and impact strength decreased with increasing of fiber loading. Thermogravimetric analysis showed an increasing degradation temperature of the samples with RWF. On the other hand, SEM micrographs showed good adherence between fibers and matrix with the presence of MAPP.