Jamarosliza Jamaluddin

New UV LED curing approach for polyacrylamide and poly(N-isopropylacrylamide) hydrogels

When a UV LED was used, the energy generated from its light source triggered photopolymerization to directly convert acrylamide and N-isopropylacrylamide monomers to polyacrylamide and poly(N-isopropylacrylamide) hydrogels, respectively. As compared to UV mercury lamps, a UV LED has more concentrated energy at its monochromatic wavelength (i.e. 365 nm), which can offer more efficient photopolymerization. In this study, a feasible photoinitiator was synthesised in parallel with the development of a UV LED water based hydrogel curing system. This is because the commercially available water soluble photoinitiator has no overlap in emission with the absorption wavelength of the UV LED. The water soluble photoinitiator (WSPI) was obtained from complexation of 2,2-dimethoxy-2-phenyl acetophenone and methylated-β-cyclodextrin. The results presented in this work suggested that WSPI was an excellent choice of photoinitiator for the UV LED system to achieve hydrogels with high monomer conversion (>90%). These findings give a promising alternative for hydrogel curing in various applications, including contact lenses and dental materials.

Grafting Efficiency of Lignin-Grafted-Polyacrylic Acid

Agriculture biomasses have been successfully converted into value-added products such as biocomposite plastics, furniture, papers and textiles. However, only the cellulose parts of these lignocellulosic materials are being used while other components such as lignin and wax are discarded. For a tropical country like Malaysia, banana stem is one of the sources of biomasses. Like other biomasses-based products, only cellulose part of banana stem is used while the lignin portion is discarded due to overly hydrophilic character. This water-loving property of lignin can be manipulated into specific application such as water absorbent for waste treatment. This research is aimed to synthesis water absorbent-based lignin from banana stem. The lignin had been extracted from banana stem using Kraft process prior to grafted with acrylic acid monomer (AA) in order to increase its water absorbency. The reaction was carried out via free radical polymerization in the presence of hydrogen peroxide (H2O2) as initiator and ammonium iron (II) sulfate hexahydrate as catalyst. The reaction temperature was set at 60°C. Grafting efficiency of polyacrylic acid (PAA) onto lignin backbone was determined by varying the amounts of AA monomer, lignin and initiator. The highest grafting percentage was acquired at 60% with the amount of 6ml acrylic acid, 2ml initiator and 0.2g lignin respectively.

Pineapple Leaf Fibers Coated with Polyacrylamide Hydrogel

Pineapple leaf fibers (PALF) have several advantages such as low cost, eco-friendly, and high specific strength. However, the brittleness of PALF limits its application. To overcome this limitation of PALF, it is essential to synergize the advantages of PALF with elastic properties of hydrogel. In this study, PALF was coated with polyacrylamide (PAAm) hydrogel under direct UV light exposure (UVA>300nm). Prior to this coating, PALF was alkali treated to introduce more OH group on PALF fiber. The main purpose of this study was to investigate the effect of untreated/treated PALF coated PAAm hydrogel on the flexibility of the fiber using tensile measurements. From the results, treated PALF coated PAAm hydrogel showed better results in tensile properties compared to untreated PALF due to the alkali treatment which improved the interfacial adhesion between PAAm hydrogel and fiber surface. In general, this study is precursor for further development in natural fiber coating technology.

Properties of UV-curable solvent-free pressure sensitive adhesive

In this study, the effects of methyl methacrylate (MMA), trimethylolpropane triacrylate (TMPTA), difunctional silicone urethane acrylate oligomer, and UV-dose on the adhesive properties of UV-curable pressure-sensitive adhesives (PSAs) were investigated, for further optimizing the adhesive properties to meet the requirements on high holding power and low peel strength. The results illustrated that increasing the MMA content decreased the peel strength and improved the holding power. The variation of TMPTA content from 1 to 10 wt% significantly enhanced the holding power from 1 h to above 120 h. The gel fraction increased with increasing TMPTA content. This increment was caused by the cross-linking of TMPTA after UV exposure. The peel strength of UV-curable PSAs was reduced to zero when oligomer content was more than 40 wt%, whereas the holding power was significantly enhanced from 5 h to above 120 h as the oligomer content increased up to 70 wt%. When the UV-dose increased, the peel strength decreased and the holding power increased. Therefore, UV-curable PSAs with very low peel strength and high holding power above 120 h were successfully synthesized and they possessed desirable features which could be fabricated to meet the specific requirements for industrial applications.

Structural, Thermal, Mechanical and Rheological Properties of Polylactic Acid/Epoxidized Soybean Oil/Organoclay Blends

Plastics are manufactured from non-degradable polymers such as polystyrene, polyethylene and many more, in which their light weight and long-lasting property are causing terrible environmental pollution. To overcome the problem, researchers are exploring on biodegradable materials that can substitute conventional polymers. Among the biodegradable polymers, polylactic acid (PLA) is a biodegradable aliphatic polyester derived from lactic acid, which can be obtained from the fermentation of starchy materials (Mehta et al., 2006). In spite of many attractive properties of PLA, such as biodegradability, high strength and modulus, PLA shows lower flexibility and higher cost, thus limiting the applications of PLA (Rasal et al., 2010). Epoxidized soybean oil (ESO) is an epoxidized derivative of a mixture of esters of glycerol with various saturated and unsaturated fatty acids. In previous study, ESO has been used as a plasticizer in PLA with 38% increase in elongation at break with 20 parts per hundred (phr) ESO loading (Ali et al., 2009). However, the tensile strength, yield stress and modulus of PLA decreased with addition of plasticizer. It has been reported that addition of plasticizer generally increases the elongation at break but decreases the strength and modulus. Thus, one method that can be used to improve the properties of polymer matrix is by incorporating fillers such as clay (Pluta et al., 2006a; Najafi et al., 2013). Incorporation of clay into PLA exhibited improvement in water vapor barrier and antimicrobial properties (Rhim et al., 2009; Castro-Aguirre et al., 2018). There are two methods that can be used to disperse the clay in polymer matrices: solution blend and meld blend. In the solution blend method, solvent is used in large amount to dissolve the polymers thus, improving the intercalation of polymer chains and clay platelets (Ozdemir et al., 2016). Whereas, for melt blend method, the layered silicate is mixed with the polymer matrix at the melting temperature of the polymer. This method is mostly used as it is more environmental friendly and polymers can be melt processed. It has been reported that the PLA/​clay nanocomposites were prepared by melt blending of PLA with sepiolite and halloysite clays (Russo et al., 2014). The addition of oligo(є-caprolactone) as compatibilizer has improved the dispersion of silicate layers in nanocomposites (Ray et al., 2002). Enhancement of properties such as crystallization rate (Pluta et al., 2006b), tensile, impact strength, modulus (Najafi et al., 2015), gas permeability, water barrier property (Şengul et al., 2017) and biodegradability (Castro-Aguirre et al., 2018) were observed in PLA/​clay nanocomposites. Dispersion of clay is very crucial in obtaining homogeneously dispersed filler in polymer matrix, in which, dispersion of clay in PLA matrix using electric effect was reported by Geun et al. (2016). Thus, this study aimed to prepare PLA blend using ESO as a plasticizer and Cloisite 30B as an organoclay. The PLA/​ESO/​organoclay nanocomposites were melt mixed with different ratios of organoclay and then investigated the structural, thermal, mechanical and rheological properties of the nanocomposites.

Preliminary study on degree of conversion of uv curable maleinated acrylated epoxidised palm oil pressure sensitive adhesives synthesised with isobornyl methacrylate monomer via FTIR-ATR analysis

UV curable PSA of maleinated acrylated epoxidised palm oil (MAEPO) from palm oil via UV LED lamp has been introduced with the existence of Chivacure 300 as photoinitiator. By involving the isobornyl methacrylate (ISBMA) as a monomer in the PSA formulation, the degree of conversion recorded low percentage of conversion, which was below 50 % although the loading of photoinitiator has been raised to 5 parts per hundred (phr). The ISBMA has affected to the slow curing speed on the maleinated PSA and restricted the conversion of C=C to more than 50 % even though the curing time and photoinitiator loading has been increased up to 300 min and 5 phr. It is expected that the double bonds are still present in the synthesised of PSA which indicated that most molecules were bonded at one end of another in methacrylate group. In the present study, real-Time FTIR-ATR spectroscopy was used to follow the crosslinking process of the adhesive and the adhesive properties of the cured coatings.

Mechanical Properties of the ‘Stretchable’ Polyacrylamide-Gelatin Double Network Hydrogel

Double network (DN) hydrogels have drawn considerable attention as innovative materials possessing both high water content as well as improved mechanical properties. In this study, DN hydrogels were formed from a combination of two hydrogel networks. The first network composed of acrylamide (AAm) and N’,N’-methylenebisacrylamide (MBAAm). AAm and MBAAm were covalently crosslinked via photopolymerization simultaneously with/without the presence of the second network pre-gel mixture; physically crosslinked gelatin-calcium carbonate (GCa). The mechanical properties characterization of the hydrogels revealed that tensile strength, Young’s modulus and elongation at break increased with the increasing amount of second network component; i.e. GCa. These data could confirmed that the polyacrylamide (PAAm)-GCa DN hydrogels possessed ‘stretchability’ character. Overall, PAAm-GCa DN hydrogels had shown better mechanical strength than the PAAm single network hydrogels. We foreseen that DN hydrogels are highly potential to be developed as artificial muscles.

Curing Properties of UV-Cured Pressure Sensitive Adhesives

In this study the effect of trimethylopropane triacrylate (TMPTA) content as a crosslinking agent on curing properties of UV-cured pressure sensitive adhesives (PSAs) was investigated. The curing properties were studied using gel fraction determination, photo-differential scanning calorimetry (photo-DSC) and Fourier transform infraredattenuated total reflection (FTIR-ATR) spectroscopy. Gel fraction sharply increased after expose to UV irradiation and increased with increasing TMPTA content. Moreover, the addition of TMPTA as crosslinking agent induced an earlier onset of auto acceleration and relative concentration of the C=C was not zero because they were trapped in the PSAs network.