Papers by Author: Nadia Adrus

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Authors: Nur Farizah Ayub, Shahrir Hashim, Nadia Adrus
Abstract: Recent trends show that the UV LED light source can greatly reduce environmental effect without compromising performance as compared to conventional UV mercury-based lamp (UV Hg) system. In this study, the possibility of using UV LED technology for photopolymerization of polyacrylamide (PAAm) hydrogels is presented. This has strongly drives the needs for suitable water-soluble photoinitiator formulation. Specifically, the photoinitiator must possess characteristic wavelength within UV LED range as UV LED emits monochromatic light sources only (365 nm or 385 nm). Here, the commercially available photoinitiator Oligo [2-hydroxy-2-methyl-1-[4-(1-methylvinyl) phenyl] propanone] (Chivacure 300) was chosen. However, Chivacure 300 has limited solubility in water. Hence, addition of tetrahydrofuran (THF) at various ratios was required. The results demonstrated that 9.5:0.5 ratio of water/THF was the minimum ratio needed for the solubility of Chivacure 300. After the synthesis of PAAm hydrogels, almost complete conversion of hydrogels was achieved (> 80 %). The highest conversion was achieved with formulation of Chivacure 300 in 9.5:0.5 ratio of water/THF. At this ratio, the hydrogels obtained were transparent. With increasing ratio of THF in water, the appearance of hydrogels gradually changed to cloudy. Indeed, UV LED technology can be used to polymerize PAAm hydrogels with comparably high conversion to conventional UV Hg system.
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Authors: Nadia Adrus, Nur Farizah Ayub, Nurul Atika Mohd Amer, Jamarosliza Jamaluddin
Abstract: 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.
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Authors: Siti Khairunisah Ghazali, Nadia Adrus, Jamarosliza Jamaluddin
Abstract: 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.
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Authors: Nadia Adrus, Mathias Ulbricht
Abstract: We report here on the characterization of classical bulk poly (N-isopropylacrylamide) (PNIPAAm) hydrogel networks. The classical PNIPAAm hydrogels were prepared from N-isopropylacrylamide (NIPAAm) as a main monomer and N,N-methylenebisacrylamide (MBAAm) as a crosslinker. The viscoelastic character of bulk hydrogels was examined using rheological measurements under frequency sweep mode (20 °C). A range of frequency, ω from 0.1 to 100 rad/s, was employed as this is a typical range for rubber plateau. Within this range, almost frequency independent of storage moduli (G'; ~ 104 Pa as a function of hydrogel compositions were obtained. Indeed, the perfect soft-rubbery behaviour of PNIPAAm hydrogels could be confirmed and thus enabled the estimation of mesh size. Interestingly, the mesh size rubbery hydrogels determined from rheological data was in a good agreement to that from swelling experiments (~ 4 to 9 nm).
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Authors: Nur Farizah Ayub, Shahrir Hashim, Jamarosliza Jamaluddin, Roshafima Rasit Ali, Nadia Adrus
Abstract: Current studies showed that UV LED system is a green technology and highly efficient as compared to UV Mercury (UV Hg) system. In this study, the UV LED curing formulations of polyacrylamide (PAAm) hydrogels were developed. The formulations consisted of acrylamide (AAm) as a main monomer, N,N’-methylenebisacrylamide as a crosslinker and photoinitiator. UV LED emits monochromatic light sources only (365 nm or 385 nm). Thus, in order to developed formulation of UV LED curable hydrogels, a suitable water soluble photoinitiator (i.e. λ ~ 365 nm) has to be employed. A commercially available photoinitiator Oligo [2-hydroxy-2-methyl-1-[4-(1-methylvinyl) phenyl] propanone] under the trade name Chivacure 300 (λ ~ 330 nm) was chosen in the first formulations. However, due to limited solubility in water, addition of tetrahydrofuran (THF) at 9.5:0.5 ratio of water/THF was required for Chivacure 300. We also synthesized a photoinitiator based on 2,2-dimethoxy-2-phenyl acetophenone (DMPA) and methylated-β-cyclodextrin (MβCD) to be used in the second formulation. The complexation of DMPA and MβCD resulted in transparent and water-soluble supramolecular-structured photoinitiator (SSPI) (λ ~ 330 nm). Both formulations were irradiated using UV LED system (Hoenle AG, Germany, 365 nm) for 15 min. Synthesis of PAAm hydrogels with both photoinitiators has yielded almost complete conversion of hydrogels (> 80 %). Clearly, this study has revealed that enhanced formulation of UV LED curable hydrogels are due to appropriate choice of excellent water-solubility photoinitiators (Chivacure 300 and modified DMPA). We concluded that UV LED is an important tool for curing hydrogel formulations of various acrylate water-based monomers.
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