Research in Polymer Chemistry using Local Raw Materials

An inaugural lecture delivered at the University of Malaya, 11 Febuary 2004

Applications of Microcapsules in Self-Healing Polymeric Materials

Self-healing polymeric materials have a great potential to be explored and utilized in many applications such as engineering and surface coating. Various smart materials with self-healing ability and unique self-healing mechanisms have been reported in recent publications. Currently, the most widely employed technique is by embedding microcapsules that contain a healing agent into the bulk polymer matrix. When cracks develop in the polymer matrix, the curing agent is released from the microcapsules to cross-link and repair the cracks. Microencapsulation of the healing agent in the core can be achieved by in situ polymerizing of shell material. This chapter presents a general review on self-healing materials, and particularly, self-healing of epoxy matrices that includes epoxy composite and epoxy coating by microencapsulation technique. Microencapsulation processes, including types of resin used, processing parameters such as core/shell ratio, concentration of emulsifiers, viscosities of aqueous and organic phases and stirring rate are discussed

A review of natural fiber reinforced poly(Vinyl alcohol) based composites: application and opportunity

Natural fibers are fine examples of renewable resources that play an important role in the composites industry, which produces superior strength comparable to synthetic fibers. Poly(vinyl alcohol) (PVA) composites in particular have attracted enormous interest in view of their satisfactory performance, properties and biodegradability. Their performance in many applications such as consumer, biomedical, and agriculture is well defined and promising. This paper reviews the utilization of natural fibers from macro to nanoscale as reinforcement in PVA composites. An overview on the properties, processing methods, biodegradability, and applications of these composites is presented. The advantages arising from chemical and physical modifications of fibers or composites are discussed in terms of improved properties and performance. In addition, proper arrangement of nanocellulose in composites helps to prevent agglomeration and results in a better dispersion. The limitations and challenges of the composites and future works of these bio-composites are also discussed. This review concludes that PVA composites have potential for use in numerous applications. However, issues on technological feasibility, environmental effectiveness, and economic affordability should be considered

Production of Medium Chain Length Polyhydroxyalkanoates From Oleic Acid Using Pseudomonas Putida Pga1 by Fed Batch Culture

Bacterial polyhydroxyalkanoates (PHAs) are a class of polymers currently receiving much attention because of theirpotential as renewable and biodegradable plastics. A wide variety of bacteria has been reported to produce PHAsincluding Pseudomonas strains. These strains are known as versatile medium chain length PHAs (PHAs-mcl) producersusing fatty acids as carbon source. Oleic acid was used to produce PHAs-mcl using Pseudomonas putida PGA 1 bycontinuous feeding of both nitrogen and carbon source, in a fed batch culture. During cell growth, PHAs alsoaccumulated, indicating that PHA production in this organism is growth associated. Residual cell increased until thenitrogen source was depleted. At the end of fermentation, final cell concentration, PHA content, and productivity were30.2 g/L, 44.8 % of cell dry weight, and 0.188 g/l/h, respectively

PRODUCTION OF MEDIUM CHAIN LENGTH POLYHYDROXYALKANOATES FROM OLEIC ACID USING Pseudomonas putida PGA1 BY FED BATCH CULTURE

Bacterial polyhydroxyalkanoates (PHAs) are a class of polymers currently receiving much attention because of theirpotential as renewable and biodegradable plastics. A wide variety of bacteria has been reported to produce PHAsincluding Pseudomonas strains. These strains are known as versatile medium chain length PHAs (PHAs-mcl) producersusing fatty acids as carbon source. Oleic acid was used to produce PHAs-mcl using Pseudomonas putida PGA 1 bycontinuous feeding of both nitrogen and carbon source, in a fed batch culture. During cell growth, PHAs alsoaccumulated, indicating that PHA production in this organism is growth associated. Residual cell increased until thenitrogen source was depleted. At the end of fermentation, final cell concentration, PHA content, and productivity were30.2 g/L, 44.8 % of cell dry weight, and 0.188 g/l/h, respectively.Keywords: Biodegradable plastics, medium-chain-length polyhydroxyalkanoates (PHAs-mcl), oleic acid, Pseudomonasputida PGA 1, fed batch fermentatio

Hexa-μ2-acetato-κ12 O:O′-μ3-oxido-tris­[aqua­chromium(III)] nitrate acetic acid solvate

In the crystal structure of the title salt, [Cr3(C2H3O2)6O(H2O)3]NO3·CH3CO2H, the trinuclear [Cr3(CH3CO2)6O(H2O)3] cluster cation has an oxide O atom that is connected to three water-coordinated CrIII atoms, the three metal atoms forming the points of an equilateral triangle. Each of the six acetate carboxyl­ate groups bridges a Cr–O–Cr fragment. The cluster cation inter­acts with the nitrate counter-ion and solvent mol­ecules through O—H⋯O hydrogen bonds, forming a three-dimensional hydrogen-bonded network

Effects of PTFE micro-particles on the fiber-matrix interface of polyoxymethylene/glass fiber/polytetrafluoroethylene composites

Reinforcing polyoxymethylene (POM) with glass fibers (GF) enhances its mechanical properties, but at the expense of tribological performance. Formation of a transfer film to facilitate tribo-contact is compromised due to the abrasiveness of GF. As a solid lubricant, for example, polytetrafluoroethylene (PTFE) significantly improves friction and wear resistance. The effects of chemically etched PTFE micro-particles on the fiber-matrix interface of POM/GF/PTFE composites have not been systematically characterized. The aim of this study is to investigate their tribological performance as a function of micro-PTFE blended by weight percentage. Samples were prepared by different compositions of PTFE (0, 1.7, 4.0, 9.5, 15.0 and 17.3 wt.%). The surface energy of PTFE micro-particles was increased by etching for 10 min using sodium naphthalene salt in tetrahydrofuran. Tribological performance was characterized through simultaneous acquisition of the coefficient of friction and wear loss on a reciprocating test rig in accordance to Procedure A of ASTM G133-95. Friction and wear resistance improved as the micro-PTFE weight ratio was increased. Morphology analysis of worn surfaces showed transfer film formation, encapsulating the abrasive GF. Energy dispersive X-ray spectroscopy (EDS) revealed increasing PTFE concentration from the GF surface interface region (0.5, 1.0, 1.5, 2.0, 2.5 µm)

Optimization of microencapsulation process for self-healing polymeric material

A series of poly(urea-formaldehyde) (PUF) microcapsules filled with dicyclopentadiene (DCPD) was successfully prepared by in situ polymerization. The effect of diverse process parameters and ingredients on the morphology of the microcapsules was observed by SEM, optical microscopy (OM) and digital microscopy. Different techniques for the characterization of the chemical structure and the core content were considered such as FT-IR and 1H-NMR as well as the characterization of thermal properties by DSC. High yields of free flowing powder of spherical microcapsules were produced. The synthesized microcapsules can be incorporated into another polymeric host material. In the event the host material cracks due to excessive stress or strong impact, the microcapsules would rupture to release the DCPD, which could polymerize to repair the crack

Microcapsules Filled with a Palm Oil-Based Alkyd as Healing Agent for Epoxy Matrix

One of the approaches to prolong the service lifespan of polymeric material is the development of self-healing ability by means of embedded microcapsules containing a healing agent. In this work, poly(melamine-urea-formaldehyde) (PMUF) microcapsules containing a palm oil-based alkyd were produced by polymerization of melamine resin, urea and formaldehyde that encapsulated droplets of the suspended alkyd particles. A series of spherical and free-flowing microcapsules were obtained. The chemical properties of core and shell materials were characterized by Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and proton nuclear magnetic resonance spectroscopy (1H-NMR). Differential scanning calorimetry (DSC) analysis showed a glass transition around −15 °C due to the alkyd, and a melting temperature at around 200 °C due to the shell. Thermogravimetric analysis (TGA) results showed that the core and shell thermally degraded within the temperature range of 200–600 °C. Field emission scanning electron microscope (FESEM) examination of the ruptured microcapsule showed smooth inner and rough outer surfaces of the shell. Flexural strength and microhardness (Vickers) of the cured epoxy compound were not affected with the incorporation of 1%–3% of the microcapsules. The viability of the healing reactions was demonstrated by blending small amounts of alkyd with epoxy and hardener at different ratios. The blends could readily cure to non-sticky hard solids at room temperature and the reactions could be verified by ATR-FTIR