Soo Tueen Bee

Review of Nanocellulose Polymer Composite Characteristics and Challenges

ABSTRACT The nanosize cellulose has emerged in the last two decades as an efficient strategy to improve the structural and functional properties of polymer composite. This review focuses to explore the unique mechanical–thermal properties of cellulose-based nanocomposites particularly on the various reinforcing mechanisms of nanocellulose. The promising reinforcing capabilities of nanocellulose mainly lie in their intrinsic chemical natures, aspect ratio, and degree of crystallinity. In this article, the potential factors deteriorating the aspect ratio and crystallinity have been systematically reviewed. Some relevant suggestions/solutions were also widely exploited toward tailoring the generating problems. GRAPHICAL ABSTRACT

Electron beam irradiation of zinc borate flame retardant containing acrylonite-butadiene-styrene (ABS) composites

The effects of electron beam radiation and zinc borate on the mechanico-physical properties and flame resistivity of magnesium hydroxide (MOH)- acrylonitrile butadiene styrene (ABS) composites have been investigated. The increasing of irradiation dosages has gradually improved the tensile strength and gel content of all samples by inducing the degree of crosslinking networks formed in ABS matrix. Analysis shows that higher amount of zinc borate is desirable to achieve promising tensile strength because zinc borate can attach into the interfaces between MOH particles and ABS matrix. Moreover, the addition of zinc borate could also retard the flammability of ABS as evidenced by LOI results. The crosslinking networks formed could improve fire resistance by reducing the melt dripping phenomenon. This is expected because the crosslinking networks can effectively minimize the oxygen gas to penetrate through the polymer structure to participate actively in the combustion activity.

Evaluation performance of multiple plasticizer systems on the physicomechanical, crystallinity and thermogravimetry of polyvinyl chloride

Abstract The flexibility of polyvinyl chloride (PVC) materials is crucial in the production of urine bags and urinary tubing. However, the combination and concentration of plasticizers offers a variation of the plasticizing efficiency to the PVC matrix. In this study, several types of plasticizers, namely dioctyl adipate (DOA), diisononyl phthalate (DINP), dioctyl terephthalate (DOTP) and epoxidized soybean oil (ESO) were added into the PVC matrix to enhance the flexibility of PVC compounds. Increasing the plasticizer loading level improved elongation at break of PVC compounds, whereas the tensile strength, hardness and specific gravity deteriorated. In addition, DOA added to PVC compounds exhibited the highest plasticizing effect with the highest elongation at break results at lower percentages of plasticizer (≤50%). This is due to the linear chain of the DOA plasticizer promoting the slippage effect of polymer chains during stretching and thus imparting a higher flexibility. In addition, a higher loading level of plasticizer in PVC compounds also produced a marginal increment on the crystallinity and thermal stability of PVC compounds. Overall, DINP/DOA added to PVC compounds exhibited the highest flexibility effect (elongation at break) at higher percentages, but lowered tensile strength and crystallinity.

Interactions of montmorillonite and electron beam irradiation in enhancing the properties of alumina trihydrate–added polyethylene and ethylene vinyl acetate blends

This study aims at investigating the effects of electron beam irradiation on the montmorillonite and alumina trihydrate–added low-density polyethylene and ethylene vinyl acetate blends. The mechanical, flammability and electrical resistivity of the montmorillonite and alumina trihydrate–added low-density polyethylene and ethylene vinyl acetate blends were investigated. The addition of montmorillonite provided the reinforcing effect to the alumina trihydrate–added low-density polyethylene and ethylene vinyl acetate, whereby the tensile strength of 150 kGy and 250 kGy irradiated samples gradually increased with increasing of montmorillonite composition (i.e. 5 phr to 20 phr). Furthermore, the addition of montmorillonite into low-density polyethylene and ethylene vinyl acetate blends increased the limiting oxygen index and thermal decomposition temperatures of samples, thus improving the flame retardancy and thermal stability. The increasing of montmorillonite and irradiation dosage promoted the char formation during combustion. Besides, the increasing of montmorillonite loading levels gradually decreased the surface and volume resistivities of the polymer blends. The high irradiation dosages (i.e. 150 kGy and 250 kGy) were found to slightly decrease the electrical resistivity of the alumina trihydrate–added low-density polyethylene and ethylene vinyl acetate blends especially at high loading of montmorillonite. The irradiation effect improved the mobility of montmorillonite ions in polymer matrix, subsequently causing the reduction of the electrical resistivity of the polymer blends. The storage capacity of electrical charges of samples was slightly declined with the increasing of montmorillonite loading levels and irradiation dosages as shown by the dielectric constant results. The dielectric loss tangent of samples slightly increased at the increasing of montmorillonite loading level. However, the dielectric loss tangent was declined with increasing of irradiation dosages.

Roles of Calcium, Zinc, Copper and Titanium Compounds on the Degradation of Polymers

In this article, the influences of the metallic filler content upon the thermal degradability of polymer composites such as initial degradation temperature, maximum degradation temperature and char content have been critically reviewed using thermogravimetric analysis. Besides that, the review on the relationship between activation energies of polymer/metal composites, which was obtained from various degrade models, and the content of metallic fillers have also been defined. Other thermal properties such as glass transition temperature (Tg) and melting temperature (Tm) have also been reviewed based on the evaluation of differential scanning calorimetry (DSC) analysis. GRAPHICAL ABSTRACT

Interaction simulation and experimental physico-mechanical analysis of distinct polarity blends of polyethylene and polyvinyl alcohol

Abstract This paper aimed to investigate the interaction of distinct polarity polymer blends of polyethylene and polyvinyl alcohol (PVOH). Molecular mechanics and dynamics simulation were employed to determine the stability of polyethylene and PVOH complexes. It was found that the binding energies ΔE for all complexes of polyethylene and PVOH are negative values indicating that the interactions between both components are favorable to achieve a lower energy hierarchy. Such interactions are induced by the high polarity hydroxyl groups of PVOH which caused weak distortion to the dipole moment of inherently non-polar polyethylene. Furthermore, the molecular simulation results were compared with tensile strength, X-ray diffraction and morphology analyses. Tensile strength analysis revealed there was a reduction of magnitude for varying PVOH before achieving a maximum value. Adding small quantities of PVOH in polyethylene as the different polar elements would affect the ordered structure within the blends. Nevertheless, the reduction is insignificant due to the polarity of PVOH which has a slightly distorted polar network of polyethylene. The addition of PVOH (5–15 parts per hundred) into a polyethylene matrix has significantly reduced the crystallinity of the polyethylene matrix by disturbing the highly ordered arrangement structures.

Investigation of enhancing effect of nano-montmorillonite on fire-retardant added low-density polyethylene–ethylene vinyl acetate hybrid system

In this study, nano-montmorillonite (NMMT) was incorporated in alumina trihydrate (ATH) added low-density polyethylene–ethylene vinyl acetate (LDPE-EVA) for enhancing the mechanical and electrical properties of the hybrid blends. The Young’s modulus of 50 phr ATH added LDPE-EVA (LE) blends has improved significantly, when the NMMT loading level increased from 5 to 15 phr. This is because the intercalation of NMMT particles reduces the cavities while enhancing the interfacial adhesion between the particle surface and LE matrix as observed via morphology analysis. The good interfacial adhesion could effectively transfer the stress from polymer matrix to filler’s particles during straining and improved the mechanical properties. On the other hand, the volume resistivity of 5 phr added LE blends was gradually decreased as the loading level of ATH has increased from 50 to 150 phr. The surface and volume resistivity of LE blends exhibited that high polarity of ATH and NMMT molecules could increase the mobility of charges in passages through polymer matrix and surface. Thus, the incorporation of ATH and NMMT could reduce the electrical resistance of LE blends. In addition, the increasing of ATH loading level also improved fire resistivity of LE blends as indicated by the promising limiting oxygen index. This is because the endothermic reaction of ATH during combustion process could reduce the temperature of polymer blends while releasing water vapour and the formation of alumina char. Furthermore, the increasing of NMMT loading level in ATH-added LE blends was found to slightly increase the fire retardancy. This is due to the addition of NMMT that could promote the dripping characteristics and charring effect during combustion and subsequently improve the fire retardancy of ATH added LE blends.

Approaches to Improve Therapeutic Efficacy of Biodegradable PLA/PLGA Microspheres: A Review

ABSTRACT This review aims to provide a comprehensive overview about various innovative strategies that have been employed by recent researchers to overcome with the shortcomings associated with traditional microspheres. Essentially, optimization strategies from structural aspects have been widely investigated to improve the properties (e.g., enhanced hydrophilicity, reduced initial burst release, etc.) of the pristine microspheres. These include bulk alteration, surface modification as well as the formation of sophisticated microsphere design such as core-shell structures. Other than that, various microencapsulation techniques and novel technologies such as spray drying, supercritical fluid technique, membrane, and microfluidics emulsification also have been explored in this review. Additionally, the impact of formulation-related aspects on the drug encapsulation efficiency, particles size and particles size distribution during double emulsification method will also be discussed and reviewed extensively based on the recent literatures reported.

Mechanical Behaviour of the Polypropylene-Devulcanized Natural Rubber Compound upon Natural Weathering

This study aims to investigate the mechanical behaviour of the polypropylene/devulcanized natural rubber (PP-DeVulcNR) compound upon natural weathering. The DeVulcNR was used to improve the mechanical properties of the PP-DeVulcNR compound at the range of 0 – 20 phr. These samples were subjected to natural weathering test at a duration range of 0 – 6 months to further study the weatherability of the compound. It was found that with the addition of 5 phr DeVulcNR in PP has the highest weatherability as it has obtained the optimum value of the tensile strength after 6 months outdoor exposure. Besides that, there is more fibrils formation on the fractured surface due to better dispersion of DeVulcNR particles in PP matrix. The Youngs Modulus and elongation at break of the PP-DeVulcNR compounds reduced after 6 months outdoor exposure due to the embrittlement of the materials. The presence of the hydroxyl (O-H) and carbonyl (C = O) stretching vibration indicated that the photo-oxidation occurs in the compound during outdoor exposure.

Interactive effect of ammonium polyphosphate and montmorillonite on enhancing flame retardancy of polycarbonate/acrylonitrile butadiene styrene composites

The effect of two flame retardants [ammonium polyphosphate (APP) and montmorillonite (MMT)] was studied in relation to flame retardancy, mechanical properties and physical characteristics of polycarbonate (PC)/acrylonitrile butadiene styrene (ABS) blends. Moreover, the possible synergistic effect of these two flame retardant additives on the macromolecular blends was studied as well. Based on this research, it was revealed that APP- and MMT-raised loading has significantly increased the limiting oxygen index (LOI) of the resulting PC/ABS blends, which is due to the intumescence effect provoked by the incorporation of these flame retardant fillers. Incorporation of APP improved the LOI through intumescence effect while the addition of MMT led to intercalation of PC/ABS polymer matrix into the interlayer galleries of MMT particles. Besides, higher APP loading in PC/ABS blends has significantly promoted the formation of carbonaceous char residues as evidenced in TGA analysis, which indicates that addition of higher APP could improve thermal stability of PC/ABS blends. To improve the tensile strength and elongation-at-break, APP loading of 25 phr in PC/ABS blends together with various MMT loading would be suitable to ensure good dispersion and interfacial adhesion between the polymer chains and the additives. However, it is important to control the loading level of MMT as its excessive incorporation could result in flame-retarded PC/ABS blends with brittle behavior, showing weaker mechanical properties.