Nur Farizah Ayub, Shahrir Hashim and Nadia Adrus Faculty of Chemical Engineering, Universiti Teknologi Malaysia, UTM Skudai, Johor, MALAYSIA
INTRODUCTION
Research Background: Hydrogels Three dimensional network which voids consist of water [1]. Hydrogels tend to swell and retain water within its network [2]. Biomedical applications, such as drug carrier, tissue engineering and actuators [3].
Conventional Polymerization: Hydrogels is usually prepared by chemical crosslinking of acrylamide (AAm) and N,N - methylenebisacrylamide (MBAAm) in an aqueous solution [4, 5].
UV Light Source UVA system based on mercury light source was mainly used for photopolymerizationin previous study. However, it does has limitations such as Follows [6]: High energy consumption Heat generation Takes time to warming up
UV LED Systems Spectrum emission of UV LED light source was narrow. Emits wavelength at 365 nm [6]. Elimination of the harmful mercury and ozone extraction friendly technology [7]. Efficient in reducing cost associated to the maintenance and repair as well.
Photoinitiators Photoinitiator is the substance that converted to free radical when exposed to UV light [8]. Water soluble photoinitiator was needed for this development of UV LED systems. Chivacure 300 is slightly water soluble photoinitiators [9]. Chemical Structure of Photoinitiators Wavelength (nm) Solubility in water 300 400 <0.5wt% at 25 C
Objectives of the Study Synthesize polyacrylamide (PAAm) hydrogels using water soluble photoinitiator based on optimized photopolymerization conditions obtained for UVA system. To characterize the monomer conversion, of PAAm hydrogels.
METHODOLOGY
Chemicals and materials AAm (Acros Organics) n-hexane (Fisher scientific) MBAAm (Sigma-Aldrich) Chivacure 300 (Chitec,Taiwan)
Flow Chart of Methodology 7.5 g of AAm and 50 ml of distilled water and stirred. 5 wt% of MBAAm was added. 2 wt% of Chivacure 300 was used for polymerization process. The mixture was exposed to UV LED lights source for 15 min The hydrogels was characterized using TOC
RESULTS & DISCUSSIONS
Results Table 1: Conversion from TOC and physical properties of PAAm hydrogels with various ratio of water/thf in photoinitiator solution
Discussions The ratios of water/thf were varied from 9.5:0.5 to 2:1 for preparation of photoinitiator solution. Ratio 9.5:0.5 photoinitiator solution -the pre-gel mixture was almost transparent. The mixture became more cloudy and white as the ratio increased up to 2:1. AAm chains collapsed and precipitated when THF was added act as an precipitation agent. All compositions in water/thf with almost complete monomer conversion (> 80 %) was achieved (Table 1).
Increasing ratio of water/thf in photoinitiator solution from 4:1 to 2:1 -decrease in the monomer conversion. PAAm hydrogels with 9.5:0.5 water/thf was transparent and homogenous conventional hydrogel. High ratio of water/thf, hydrogels appeared to be cloudy. Transparent and homegenous, higher monomer conversion of hydrogels.
Conclusions PAAm hydrogels yielded a conversion of > 80% using UV LED curing system Purely water soluble photoinitiator in photopolymerization was expected to produce high monomer conversion of hydrogels with transparent appearance. UV LED system demonstrated efficient photopolymerization of PAAm hydrogels.
Acknowledgements The author thanks Ministry of Higher Education Malaysia and Universiti Teknologi Malaysia for Research University Grants (Vot. No: 08J22 and 06H99), ERGS (Vot. No: 4L142) and Zamalah Institutional Scholarship provided by UTM.
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