Impact of carboxylation and hydrolysis functionalisations on the anti-oil staining behaviour of textiles grafted with poly(N-isopropylacrylamide) hydrogel

Novel hydrogel-modified textiles have been prepared through photografting poly(N-isopropylacrylamide) (PNIPAAm) onto pristine and functionalised polyethylene terephthalate (PET) surfaces. In this work, two types of functionalisation, carboxylation (CPET) and hydrolysis (HPET), were performed to scrutinise the hydrogel grafting efficiency. Basic characterisation of the pristine, functionalised and grafted textiles was carried out via fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) analyses. Then, the functional characteristics of these samples were determined based on the oil staining performance. Functionalisation of the PET textiles via hydrolysis and carboxylation gives rise to different chemical reactivity and interactions on the PET surface. Impressively, the surface formed via hydrolysis functionalisation of PET was found to be more efficient compared to that formed via carboxylation, and the untreated one. The HPET surface was remarkably more hydrophilised and rougher than both the UPET and CPET surfaces. The accessibility of the -OH groups for hydrogen abstraction from HPET has a great impact on the hydrogel grafting onto the HPET surface. All the grafted textiles (PNIPAAm-g-UPET, PNIPAAm-g-CPET and PNIPAAm-g-HPET) demonstrated anti-oil staining behaviour at 27 °C. In particular, PNIPAAm-g-HPET textiles with a high degree of grafting (DG) exhibited the fastest rate for oil to de-stain from the surface. Moreover, the reversible transition of PNIPAAm hydrogels around the lower critical solution temperature (LCST) ~ 32 °C from hydrophilic to hydrophobic generates switchable surfaces of the textiles with regard to the oil wettability. Specifically, PNIPAAm-g-HPET textiles also displayed the highest degree of wettability switching as a result of having the highest DG. Taken together, the PNIPAAm hydrogels grafted onto PET textiles were significantly enhanced though hydrolysis functionalisation and possessed excellent switchable surfaces toward oil-staining, having great potential to be used for applications in oil and water separation as well as smart textiles

Biodegradable and temperature-responsive thermoset polyesters with renewable monomers

A series of biodegradable thermoset polyesters, poly(1,8-octanediol–glycerol–dodecanediaote)s (POGDAs), were synthesized with the polycondensation polymerization method without a catalyst and with different monomer molar ratios. Synthesis was confirmed with structural analysis via Fourier transform infrared spectroscopy. The effect of varying the monomer molar ratio on the material properties was illustrated in the gel content and swelling analysis, ultraviolet–visible spectroscopy, differential scanning calorimetry, X-ray diffraction, and degradation tests. Degradation tests were performed in phosphate-buffered solution at 37 °C for 60 days. Temperature-responsive behavior was revealed with POGDA (0.5 glycerol), and bending tests were performed to study the shape-memory effect. In vitro cytotoxicity tests and cell proliferation tests suggested that these POGDAs have potential applications in biomedical fields such as tissue engineering

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-ß-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

Optimization of pineapple leaf fibre extraction methods and their biodegradabilities for soil cover application

Cellulosic natural fibres from pineapple leaves are considered as a green alternative to the conventional polyethylene (PE) soil cover in agro-industry. The use of pineapple leaf fibres (PALFs) soil cover can overcome the disposal problem of the conventional plastic covers which take hundreds of years to degrade. This research was undertaken to study the effectiveness methods of extracting the PALFs. The mechanical method utilized ‘roller and bladder system’, where the chemical method involved the extraction with 6% NaOH, 20% aqueous acetone, and pineapple juice solution. The semi-mechanical method was a combination of “roller and bladder” system and a chemical retting process using 6% NaOH alkaline solutions. The characteristics of the extracted fibers were determined using X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Kappa number test of the fibres extracted with semi-mechanical method showed the lowest percentage of lignin (3.39%). Based on XRD results, the highest percentage of crystallinity was recorded when PALF was extracted using the semi-mechanical method. A remarkable change on the morphological surface the biodegraded PALF soil cover was observed after 90 days of soil burial test. Biodegradability of soil cover made from PALF was higher than the commercial degradable soil cover i.e. PE/starch (80 wt% PE/ 20 wt% starch). Meanwhile, the growing rate and the soil fertility of chili tree that used PALFs soil cover showed better results than the chili tree that used conventional PE/starch soil cover

A review on recent approaches to sustainable bio-based epoxy vitrimer from epoxidized vegetable oils

Epoxidized vegetable oil (EVO) – based epoxy vitrimer is a promising bio-based material to replace the non-recyclable and ever-increasing petrol-based thermoset. However, the low overall properties of EVO-based epoxy vitrimer are relatively unmatchable to petrol-based thermoset, retarding the substitution of EVO-based epoxy vitrimer into the application range of petrol-based thermoset. To fill the research gap, we review the recent approaches and important characteristics of EVO-based epoxy vitrimer, including the selection of EVO, classification of covalent adaptable network (CANs) and, material properties. Their potential applications and outlooks are discussed as an implication for future development. For EVO-based epoxy vitrimer, EVOs with higher mean epoxy values are suggested to be selected as epoxy monomer in order to produce a vitrimer with greater tensile properties and higher glass transition temperature, Tg. Types of CANs incorporated in EVO-based epoxy vitrimer are not yet fully explored as only 3 types of CANs (transesterification, Schiff base and disulphide exchange) have been reported currently. The mechanical properties and Tg of EVO-based epoxy vitrimer can be improved by using curing agent with rigid structure and avoid using aqueous-based curing agent during synthesis process. Thermal stability of EVO-based epoxy vitrimer is affected by crosslinking density and the structure of curing agent. It is envisaged that EVO-based epoxy vitrimer with greater properties can be developed to replace the traditional petrol-based thermoset, provided that effective EVO, appropriate CANs and suitable curing agent are selected

Methacrylic Acid Based Polymer Networks with a High Content of Unfunctionalized Nanosilica: Particle Distribution, Swelling, and Rheological Properties

The poor stability and tendency to agglomerate of unfunctionalized nano-SiO2 in the presence of ionic species presents a challenge for preparing poly(methacrylic acid)/nano-SiO2 nanocomposite (NC) hydrogels with desired strength and swelling capability. We proposed a facile and eco-friendly method for the preparation of PMAA/SiO2 NC hydrogels using unfunctionalized silica nanoparticles (NPs) in the form of a suspension. SEM and TEM analyses showed that the NP distribution in the polymer matrix highly depended on the particle concentration. At lower concentrations (up to 13.9 wt %), the NPs were uniformly dispersed as single nanoparticles. With an increase in NP concentration, homogeneously dispersed nanoscale aggregates were formed, while a further increase in the silica concentration led to the formation of homogeneous structures consisting of mutually interacting nanosilica particles coated with PMAA. Swelling experiments confirmed that the silica NPs behaved as adhesive fillers that interacted with PMAA chains, causing the formation of a thin polymer layer strongly adsorbed at the particle interface. The thicknesses of the adsorbed polymer layer, as well as the swelling kinetic parameters, were strongly influenced by nanoparticle size and concentration. Combining nanosilica and PMAA in the form of a soft hydrogel network provided stabilization of the NPs and ensured better mechanical properties of the obtained NC hydrogels compared to pure polymer matrix. The optimal loadings, necessary to ensure the most improved dynamical-mechanical properties, were found in the case of the formation of homogeneously dispersed, nanosized silica aggregates in a PMAA matrix