Stimuli-responsive Hydrogele und Poren-gefüllte Hydrogel Kompositmembranen

Classical bulk temperature-responsive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels were prepared via free radical polymerization in the presence of N,N’-methylenebisacrylamide (MBAAm) as a crosslinker. Two different initiation methods were studied: redox and photoinitiation. It was demonstrated that the desired final properties of resulting hydrogels, i.e., high monomer conversion and adjustable swelling were only achieved by selecting best suited initiation conditions. For redox polymerization, this was done by tuning the ratio of accelerator N,N,N',N'-tetramethylenediamine to initiator ammonium persulfate. The key parameters for achieving optimum photopolymerization conditions were photoinitiator concentration and UV irradiation time. With the help of in situ rheological measurements, optimum conditions could be further verified and quantified by monitoring the liquid-to-gel transition. Overall, photoinitiated crosslinking copolymerization was postulated to offer better options for in situ preparation of tailored functional hydrogels. Therefore the classical photopolymerized bulk PNIPAAm hydrogels were characterized in more details (swelling and mesh size, swelling recovery, volume expansion factor relative to synthesis state, morphology and partitioning of test solutes) as compared to redox hydrogels (swelling and mesh size). Rheology was also used to investigate the hydrogel after ex situ preparation, revealing “perfect” soft-rubbery behaviour. A good correlation between the mesh sizes determined from swelling and rheology was also found. Rheology has been found to be a powerful tool because it provides valuable data on polymerization and gelation kinetics as well as information about the hydrogels microstructure based on their viscoelastic character. The resulting optimum conditions from this part were utilized towards preparation and characterization of smart hydrogels that can respond to multiple stimuli and also functional pore-filling composite membranes. Temperature-responsive PNIPAAm hydrogels were imprinted with lysozyme via in situ photoinitiated crosslinking copolymerization. The three-dimensional network of the hydrogels was tailored by tuning the ionic content through methacrylic acid (MAA) as template-binding comonomer while keeping the ratio between crosslinker (MBAAm) and N-isopropylacrylamide (NIPAAm) fixed. The rheological data demonstrated that the onset of gelation was delayed with increasing MAA content. Moderate salt concentrations (0.3 M NaCl) were found to be suited for template removal without phase separation of the hydrogel. Swelling and protein (lysozyme and cytochrome C) binding were investigated for molecularly imprinted (MIP) and non-imprinted polymers (NIP) gels at temperatures below and above the lower critical solution temperature of PNIPAAm (32 °C). MIP gels showed a much higher affinity, selectivity and binding capacity for lysozyme compared to the NIP reference materials. Protein binding capacity was strongly reduced above 32 °C, to zero for NIP and to small values for imprinted gels. Most important, specific lysozyme binding to the MIP gels caused a large concentration dependent deswelling. This effect was much smaller for NIP gels, and the response could be modulated by the content of the comonomer methacrylic acid. It is envisioned that the alteration of swollen state of stimuli-responsive MIP hydrogels as functions of specific protein or temperature may govern the recognition-ability and binding-specificity towards establishment of novel biomimetic materials. A copolymer of PNIPAAm and 4-vinylbenzo-18-crown-6 (vCE) was synthesized via redox-initiation polymerization. The influence of vCE content on the copolymerization efficiency and also on the ion-recognition properties was investigated. The copolymerization was relatively efficient in a more loosely crosslinked network (rheology and Fourier transform infrared analyses). The swelling of PNIPAAm-co-vCE at 37 °C was higher in the presence of cations; i.e. Ba2+ > K+ than in pure water. The hydrogel copolymers were more sensitive at the higher ion concentration (0.02 M). The cation recognition and selectivity were further enhanced by the increase of vCE content in the hydrogel copolymers. Overall, this approach is interesting for the development of novel sensors or materials for controlled release applications. Hydrogel pore-filled composite membranes (HPFCM) based on polyethylene terephthalate (PET) track-etched membranes with pore diameters between 200 and 5000 nm and temperature-responsive PNIPAAm hydrogels were successfully prepared. A prefunctionalization of the pore walls by grafted linear PNIPAAm lead to stable anchoring of crosslinked PNIPAAm prepared in a subsequent step. Proper tuning of photopolymerization conditions resulted in desired microstructure of the hydrogels and thus tailored barrier properties of the composite membranes. The very interesting separation performance of HPFCM was due to diversification of the hydrogel network as function of its composition that caused adjustable sieving properties via synthesis conditions and also largely switchable barrier properties in response to the temperature. The interplay between the immobilized hydrogel and various pore sizes of the membrane support was also investigated. The base membrane provides mechanical support and confines the hydrogel within its pores, and it thus allows using the hydrogel mesh size for size-selective solute transport. Completely stable and selective HPFCM were only obtained with base pore sizes of about 2 µm or smaller. The size-selectivity (molecular weight cut-off) of the same HPFCM was higher under diffusive than under convective flow conditions; this is presumably mainly caused by elastic deformation of the hydrogel network. The cut-off from diffusion experiments was well correlated to mesh-size of the hydrogel determined from the Darcy model applied to permeability data obtained under convective flow conditions. Upon temperature increase beyond 32 °C, flux increased and rejection decreased very strongly; this remarkable change between macromolecule-size selective ultrafiltration and microfiltration/filtration behaviour was fully reversible. The smart performance of HPFCM could be interesting for the separation of multi-component mixtures or for controlled release due to the tunability of the sieving coefficient by changing the temperature

Lignin-coated polystyrene/trichloromethylsilane absorbent for oil spill cleanup

The study was conducted to determine the effectiveness of lignin-polystyrene/ trichloromethylsilane (TL-PS) absorbent in removing oil spillage from wastewater. Lignin powder obtained from the delignification of oil palm empty fruit bunch (OPEFB) was coated with PS emulsion (PSE) at various concentrations (2, 4, 6, & 8 mL) in order to bind the powder into an aggregated form. Later, L-PS was exposed to trichloromethylsilane (TCMS) via chemical vapour deposition method (CVD) at fixed 7.5 min exposure time to form TL-PS absorbent. The wettability of TL-PS was determined by conducting water contact angle (WCA) measurement and oil sorption capacity. It was found that TL-PS4 sample (immersed in 8 mL PSE) had the highest WCA value (134.10°) and oil sorption capacity (52%) in comparison with L-PS4 (immersed in 8 mL PSE without TCMS) with WCA value of 99.10° and oil sorption capacity of 40%. Meanwhile, the disappearance of hydroxyl group (OH) at peak 3429 cm-1 and appearance of siloxane bonds (R-Si-O) at peak in range of 1000 - 1100 cm-1 and 3.9 - 4.0 ppm had confirmed the substitution occurred between these groups, as shown by the spectra obtained from attenuated total reflectance-Fourier transform infrared (ATR-FTIR) and nuclear magnetic resonance (NMR). Thermal stability of TL-PS4 (onset degradation temperature at 252 °C) was higher when compared with lignin (onset degradation temperature at 40 °C), as showed by the thermogravimetric analysis (TGA). Meanwhile, the surface of absorbent had change from smooth (L-PS4) to rough (TL-PS4) corresponding to the deposition of silane particles onto the surface of L-PS after the exposure with TCMS, as shown by the scanning electron microscopy (SEM). The results suggested that TL-PS has a promising potential to be used as an absorbent for oil spill cleanup

Pineapple peel based biocomposites for green packaging

In this research, pineapple peel fiber (PAPF) based low density polyethylene (LDPE) biocomposites for green packaging was studied. The PAPF was first being treated with alkali before compounded with LDPE. Then, the mixture was compounded using twin screw extruder and the test samples were prepared using hot press machine. The compatibility of the PAPF as biocomposites was observed through the characterization and biodegradation analysis. Melt flow index (MFI) analysis was conducted to determine the process ability of the biocomposites. As the fiber loading in the biocomposites increases, the MFI values were decreased. The amount of water absorption was increased with the increases of PAPF loading due to the higher cellulose content. The biocomposites was buried in the soil for a month for biodegradation analysis and the highest PAPF/LDPE loading biocomposites degraded the most

UV LED curing of hydrogel modified textiles with high anti fouling resistance

The hydrogel grafted polyethylene terephthalate (PET) textiles were envisioned to have oil-repelling properties due to the synergistic of combining hydrophilic hydrogel onto PET textiles surfaces. In this work, PAAm hydrogels were grafted i.e. via immersion or dipping methods onto pristine (PPET) and alkaline treated (APET) PET textile surfaces using UV LED light source. The obtained samples were then characterized based on the degree of grafting (DG), Fourier transformed infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), surface wettability by contact angle and oil fouling test. APET was found to be more efficient for grafting compared to the PPET due to the surface modification made after the alkaline treatment. APET surface turned to be more hydrophilic than PPET due to the presence of hydroxyl group (-OH) as proven in the FTIR. In addition, the PAAm hydrogel was confirmed to be successfully grafted onto the APET textile via immersion or dipping methods with the optimum DG obtained was at 20 minutes of UV time. This finding has also proven the potential of UV LED as a promising technology to replace the conventional UVA for hydrogel curing. Higher DG was obtained for immersed grafting sample (PAAm-g-APETimm; DG=160 wt%) when compared to the dipped sample (PAAm-g-APETdip; DG=60 wt%) which indicates that higher mass fraction of PAAm could be attached to the surface of PAAm-g-APETimm. Apart from that, PAAm-g-APETimm shows lower water contact angle (WCA) with WCA=60.90° as compared to PAAm-g-APETdip with WCA=83.15° which could be due to higher thickness of hydrophilic layer that resulted in slower rate of oil fouling performance. To summarize, the PAAm hydrogel grafted onto PET textiles were significantly improved and possessed excellent surface towards oil staining performance. By comparing both textile modifications, grafting via dipping was more preferable. Even though the DG obtained was slightly lower, its thin layer of hydrogel grafted on the APET textile surface was sufficient to de-stain oil from the textile surface at a faster rate (~0.60-0.70 seconds). To some extent; the hydrogel modified textiles via UV LED curing has bright vision in the near future as promising tools for oil/water separation

The effect of alkaline treatment onto physical, thermal, mechanical and chemical properties of lemba leaves fibres as new resources of biomass

The main purpose of this paper is to investigate the effect of alkaline treatment on the physical, thermal, mechanical and chemical properties of pristine lemba leaves fibres (LeLeFs). LeLeFs were treated with 6, 8, and 10 wt% sodium hydroxide (NaOH) solution at room temperature for 24 h. In order to determine the functional group presence after the alkaline treatment, LeLeFs were analyzed using Fourier Transform Infrared (FTIR) Spectroscopy. The density of LeLeFs treated with 10 wt% NaOH solution recorded the highest density with 1.168 g/cm3. Morphology study showed that the diameter of fibre reduced with the increment of NaOH concentration. The removal of lignin and hemicellulose could be observed in the thermogravimetric analysis (TGA). Alkaline treatment enhanced the tensile properties of fibre and 10 wt% alkaline treated fibre resulted in the highest tensile strength, modulus and elongation of the fibre at 511.10 MPa, 11.76 GPa and 3.69% respectively. Chemical resistance analysis found that the treated fibre had better chemical resistance compared to untreated fibre. Therefore, it is substantiated that alkaline treatment affects the properties of LeLeF

Molecularly imprinted stimuli-responsive hydrogels for protein recognition

Temperature-responsive poly(N-isopropylacrylamide)-based (PNIPAAm) hydrogels were imprinted with lysozyme via in situ photo-initiated crosslinking polymerization. The three-dimensional network of the hydrogels was tailored by tuning the ionic content through methacrylic acid as template-binding comonomer while keeping the ratio between crosslinker (N,N'-methylenebisacrylamide) and N-isopropylacrylamide fixed. Moderate salt concentrations (0.3 m NaCl) were found to be suited for template removal without phase separation of the hydrogel. Swelling and protein (lysozyme and cytochrome C) binding were investigated for imprinted and nonimprinted gels at temperatures below and above the lower critical solution temperature of PNIPAAm (32 °C). Imprinted gels showed a much higher affinity, selectivity and binding capacity for lysozyme compared to the nonimprinted reference materials. Protein binding capacity was strongly reduced above 32 °C, to zero for nonimprinted and to small values for imprinted gels. Most important, specific lysozyme binding to the imprinted gels caused a large concentration dependent deswelling. This effect was much smaller for nonimprinted gels, and the response could be modulated by the content of the comonomer methacrylic acid. Overall, this approach is interesting for the development of novel sensors or materials for controlled release applications

Separation functions of poly(N-isopropylacrylamide) hydrogel

Conference Objectives include; 1. To provide opportunities for researchers in field of polymeric materials to share and exchange ideas with each other. 2. To establish relationship and foster cooperation between academicians, scientist, researchers and engineers from various disciplines of polymer science and technology to form strategic R&D for a win-win situation. 3. Share and discuss the results of the study, knowledge, information and activities related to the phenomenon of polymeric materials and technology

Novel hydrogel pore-filled composite membranes with tunable and temperature-responsive size selectivity

Hydrogel pore-filled composite membranes (HPFCM) based on polyethylene terephthalate (PET) track-etched membranes with pore diameters between 200 and 5000 nm and temperature-responsive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels were successfully prepared. A premodification of the pore walls by grafted linear PNIPAAm led to stable anchoring of crosslinked PNIPAAm prepared in a subsequent step. Proper tuning of photopolymerization conditions resulted in a desired microstructure of the hydrogels and thus tailored barrier properties of the composite membranes. The very interesting separation performance of HPFCM was due to diversification of the hydrogel network that caused adjustable sieving properties via synthesis conditions and also largely switchable barrier properties in response to the temperature. The interplay between the immobilized hydrogel and various pore sizes of the membrane support was also investigated. The base membrane provides mechanical support and confines the hydrogel within its pores, and it thus allows using the hydrogel mesh size for size-selective solute transport. Completely stable and selective HPFCM were only obtained with base pore sizes of about 2 μm or smaller. The size-selectivity (molecular weight cut-off) of the same HPFCM was higher under diffusive than under convective flow conditions; this is presumably mainly caused by elasticity deformation of the hydrogel network. The apparent cut-off from diffusion experiments was well correlated to the mesh-size of the hydrogel determined from the Darcy model applied to permeability data obtained under convective flow conditions. Upon temperature increase beyond 32 °C, flux increased and rejection decreased very strongly; this remarkable change between macromolecule-size selective ultrafiltration and microfiltration/filtration behavior was fully reversible

The rubber elasticity of poly(n-isopropylacrylamide) hydrogel networks

We report here on the characterization of classical bulk poly(N-isopropylacrylamide) (PNIPAAm) hydrogel networks. The classical PNIPAAm hydrogels were prepared from Nisopropylacrylamide (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, ? 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)

Poly(N-Isopropylacrylamide) hydrogel networks and sieving characteristics

The three-dimensional of hydrogel networks within nm range can microscopically be considered as “porous”mesh. This feature may imply that hydrogel networks possess sieving characteristics; i.e. exclusion of solutes or molecules based on size. In this study the network and sieving characteristics of poly(N-isopropylacrylamide) (PNIPAAm) hydrogels were investigated. PNIPAAm hydrogels were prepared via free radical using N-isopropylacrylamide (NIPAAm) as main monomers and N,N‘-methylenebisacrylamide (MBAAm) as crosslinkers. As the composition of the hydrogels was varied, the mesh sizes of the resulting hydrogels were in the range of 4.0 to 11.0 nm. These data were obtained from swelling experiments. Dextrans as test solutes with molecular weight in the range of 4 to 2000 kg/mol were used in partitioning experiments to investigate the sieving of the hydrogel networks. The partitioning data indicated that of hydrogel networks excluded the solutes which were bigger than its mesh sizes. The experimental results not only show a good correlation of sieving coefficient on the size basis but also nicely fitted to the partition data estimated from the Ogston model. Undoubtedly, PNIPAAm hydrogel networks possessed sieving characteristics to separate molecules exclusively and selectively as a function of size