Iranian Polymer Journal
Year:2021 | Volume:30 | Issue:4|Papers Count:9

Zipper-like thermosensitive molecularly imprinted polymers (MIPs) based on konjac glucomannan (KGM) for metformin hydrochloride were prepared using KGM, a natural polysaccharide, as the matrix, acrylamide (AM) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) as the comonomers, N, N′,-methylenebis(acrylamide) as the cross-linking agent, ceric ammonium nitrate as the initiator, and metformin hydrochloride as the template molecule. The resultant MIPs were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectrometry (XPS), X-ray diffractometry (XRD), thermal gravimetric analyzing (TGA), and scanning electron microscopy (SEM). The interpolymer interactions between poly (AM) and poly (AMPS) were demonstrated by the results of ultraviolet spectrometry (UV), indicating that MIPs with zipper-like structure could be fabricated. The thermo-responsive MIPs with on/off-switchable characteristic were evaluated by the method of cyclic voltammetry (CV). The adsorption experiment showed that the target molecules could be controlled to be adsorbed/desorbed by changing the external temperature. The adsorption capacity at high temperature was higher than that at low temperature. Moreover, the adsorption capacity of MIPs was much higher than that of NIPs. The results of adsorption experiments showed that the MIPs could specifically recognize and adsorb metformin with excellent selectivity, repeatability, and stability. Langmuir equation and Freundlich equation were applied to fit the adsorption isotherms of MIPs and the results showed that the Langmuir equation fitted better than the Freundlich equation. The product is expected to serve as a novel adsorption and separation material.

A series of pH-sensitive semi-interpenetrating polymer network (semi-IPN) hydrogels poly(vinyl alcohol)/poly(hydroxypropyl methacrylate-co-methacrylic acid) (PVA/P(HPMA-co-MAA)) were synthesized by free-radical polymerization of HPMA and MAA in the presence of PVA. The physicochemical property of the obtained hydrogels was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analyses and scanning electron microscopy (SEM) measurements. The SEM photograph revealed the network formation with uniform pore distribution. The swelling behavior of each hydrogel in buffer solution showed a simultaneous sensitivity to pH and ionic strength: the swelling ratio of all hydrogels was higher in neutral environment than in acidic medium,besides, equilibrium swelling ratio of the hydrogels decreases as the ionic strength increases. Insulin was loaded into the PVA/P(HPMA-co-MAA) semi-IPN hydrogel. The in vitro insulin release experiment was carried out in buffer solutions at pHs 1. 2 and 6. 8. Results showed that the release of entrapped insulin was inhibited at pH 1. 2 but obviously increased at pH 6. 8. Cell viability revealed that the hydrogels were biocompatible. After oral administration of insulin-loaded hydrogel to streptozotocin-induced diabetic rats at 75 IU/kg, a sustained reduction in blood glucose level was observed. Therefore, the semi-IPN PVA/P(HPMA-co-MAA) hydrogels are potential vehicles for oral delivery of protein drugs.

Novel sulfonic acid-functionalized chitin nanowhiskers (sChW) with enhanced proton conductivity were prepared for fabricating green and environmentally friendly chitosan (CS)-based nanocomposite polymer electrolyte membranes (PEMs). The performance of sChW in the development of direct methanol fuel cell (DMFC) nanocomposite membranes was also assessed. The manufactured nanocomposite membranes were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), CHNS elemental analysis, X-ray diffractometry (XRD), ion-exchange capacity (IEC), water uptake, as well as proton conductivity and methanol permeability. The results showed that modification of chitin nanowhiskers (ChW) with sulfonic acid groups, as the proton-conducting sites, could enhance proton conductivity of the manufactured membranes, leading to a fall in methanol permeability, as a result of attractive interactions between the negatively charged sulfonic acid groups on the surface of sChW and the positively charged amine groups in the chitosan chains. Thus, the selectivity parameter (the ratio of the proton conductivity to methanol permeability) of the chitosan-based nanocomposite membranes significantly increased from 3900 for pristine chitosan PEM to 26, 888 S. s. cm−, 3 (ca. 6. 8 times) for a membrane with 5% (wt) sChW. The functionalization strategy used herein can pave the way for the development of efficient polyelectrolyte membranes for applications in direct methanol fuel cells.

Searching for lightweight, economic, bio-degradable, recyclable and eco-friendly material with high specific strength and high specific modulus to reinforce polymer composites finds a viable and potential solution in natural fiber. In the present work, zero cost plentifully accessible Coccinia grandis stem fiber (CGSF) with high cellulose content, specific mechanical properties and salient surface features to ensure good bonding with the polymer matrix is comprehensively characterized for its physical, chemical, thermal, mechanical, surface roughness and microstructural properties. Initially, CGSF is qualified and used as a reinforcement in the fabrication of composite with polyester resin (CGSFC). The critical length of fiber and the best percentage addition of fiber reinforcement were determined based on mechanical testing, which were found to be 40 mm and 40% (wt), respectively. Mechanical properties increased with amount of fiber up to 40% (wt), where fiber pullout, debonding and matrix failure occurred systematically to provide maximum load transfer capability to the composite. Thermal analysis of the fiber confirmed its thermal stability till 250 °, C, which is sufficient for any polymeric material. Tensile strength of about 50 MPa, better flexural strength, sufficient energy absorption capacity and hardness affirm the CGSF composite as an alternative structural material for various engineering applications.

Cross-linker plays a crucial role in monitoring water holding and drug release properties of a hydrogel system, an essential requirement for smart wound dressings. Present study is focused on the influence of cross-linkers poly ethylene glycol (PEG) and N, Nʹ,-methylene bisacrylamide (MBAAm) on the properties of poly (acrylamide-co-acrylic acid) hydrogel grafted over the cotton fabric to form composite for medicated dressings. Fourier transform infrared spectroscopy (FTIR) confirms the grafting of hydrogel on the cotton fabric. Uniform hydrogel layer on the cotton surface is obtained under scanning electron microscopy (SEM). Swelling of the composite prepared using PEG follow first-order kinetics at acidic and neutral pH whereas second-order kinetic model at pH 8. 5 while that prepared using MBAAm follow second-order kinetic equation at all the pHs studied. The swelling kinetics is also governed by Peppas model at all pHs. Release of gentamicin sulphate from both the composites are studied in phosphate buffers having pH 4. 5, 7 and 8. 5 at 37 , ±,  , 0. 1 °, C and observed that it is fastest in phosphate buffer having pH 7. On fitting drug release data into Peppas model, first and second-order kinetic equations, it is found that drug release is diffusion controlled and follows Fickian diffusion mechanism in case of the composite prepared by using PEG as cross-linker, whereas it is controlled by diffusion as well as chain relaxation in case of the composite prepared by using MBAAm. Mechanical testing using universal testing machine supports a higher mechanical strength of the hydrogel composite as compared to its film.

To study the properties of ethylene-tetrafluoroethylene (ETFE) copolymer materials in wings of unmanned aerial vehicles, electron beam irradiation was performed to prepare the corresponding irradiated ETFE for air atmosphere. All these irradiated samples were characterized by SEM, FTIR, TGA, DSC, flexural fatigue measurement and tensile test. The results revealed that the logarithm of the flexural fatigue of ETFE decreased with the irradiation dose increased, which could be explained by the growing effect of chain scission. The elongation-at-break decreased with the dose increase, while the tensile strength was kept constant. As shown in FTIR results, the scission of the macromolecular chains induced by irradiation resulted in the relative oxidation of groups, such as carbonyl groups. TGA analysis showed that the initial and maximum decomposition temperatures increased with dose increase due to the inherent cross-linking structures. Besides, the number of the crystalline regions with regular formation (such as crystallization temperature, crystallization degree and crystallization enthalpy) decreased with the dose increase as a result of the formation of unsaturated structures after the elimination of HF from the broken chains, which was confirmed by FTIR. It is expected that our findings can provide important information to promote the development of aircraft materials.

A series of catechol-modified epoxy resin biomimetic coatings (CE-X, X represents the weight fraction of catechol-modified epoxy resin, X , = , 0, 5%, 10%, 15%, 20%, 25%) with high adhesive strength on saturated concrete substrate were designed and synthesized. The chemical structures of the CE-X were confirmed by proton nuclear magnetic resonance (1H NMR), carbon-13 nuclear magnetic resonance spectroscopy (13C NMR), and Fourier transform infrared spectroscopy (FTIR). The thermal property of CE-X was characterized by thermogravimetric analysis (TGA). The adhesive properties were characterized by pull-off tests. Results showed that when the content of catechol–, epoxy resin was under 20% by weight, the adhesive strength could be further increased by forming hydrogen bonds and coordination complexes in the interface of coating and saturated concrete of the substrate. When the content of catechol–, epoxy resin was above 20% by weight, the pull-off tests showed cohesive failure, and the adhesive strength on saturated concrete substrate reached the maximum value of 4. 61 , ±,  , 0. 8 MPa, which was improved by , ~ , 3 MPa compared to that of the control sample. The adhesive properties of epoxy coatings on saturated concrete substrate could be improved by adding a proper amount of catechol groups. In addition, when it was immersed in water for 30 and 120 days, its adhesive strength was reduced by about 7. 8% and 22%, respectively. This work provides a new method for designing and synthesizing protective coatings with high adhesive strength on the saturated concrete substrate.

Nanocomposites based on thermoplastic polyurethane/polyvinyl chloride/multi-walled carbon nanotubes were prepared by a solution method and their shape memory properties were studied. The blend ratios were 70/30, 60/40, and 50/50 (w/w) of thermoplastic elastomer polyurethane/polyvinyl chloride. To improve the dispersion of multi-walled carbon nanotubes, at 0. 5% and 1% (wt), in polymer matrices, three-step chemical modifications were performed, including oxidation, chlorination and grafting of poly (ɛ,-caprolactone) diol. The occurrence of surface modifications in MWCNTs was monitored using Fourier transform infrared spectroscopy, elemental analysis, scanning electron microscopy and thermal gravimetric analysis techniques. SEM micrographs revealed a good dispersion of MWCNTs in the polymer matrix due to better matrix-filler interactions compared to filler–, filler interactions. The results showed that the main indices of shape memory behavior (shape fixity and shape recovery) of nanocomposite samples were affected by the polymer blend ratio, nanoparticle concentration and surface modification. Increasing the content of polyvinyl chloride led to reduced shape fixity and shape recovery, which was attributed to the lack of rigid structural nature of polyvinyl chloride. The presence of nanoparticles contributed to enhanced shape fixity and weaker shape recovery. This can be explained by lower polymer chain mobility in the presence of multi-walled carbon nanotubes. The reduction in chain mobility in nanocomposites reinforced by surface-modified multi-walled carbon nanotubes was more significant due to higher distribution efficiency of nano-scale fillers in the polymer matrix.

Novel highly porous cellulose triacetate (CTA)/cellulose acetate (CA) blends were fabricated as flat sheet membranes, for water desalination using the forward osmosis (FO) procedure. Maleic acid (MA) was used as a pore-forming additive and as a polymeric modifier in combined casting. The aluminum oxide nanoparticles (Al2O3) (NPs) were used for the modification of MA/CTA/CA membrane performances. The synthesized FO membranes are characterized by FTIR spectroscope, contact angle measurement, membrane porosity, SEM, AFM, and mechanical properties. The Al2O3/MA/CTA/CA nanocomposite (NC) modified membrane showed a higher water flux of 27. 1 L/m2 h, reverse solute flux of 10. 3 g/m2 h, and lower salt rejection of 99. 15% using 1 M NH4Cl water solution as the draw solution and 0. 1 M NaCl as feed solution. The Al2O3/MA/CTA/CA nanocomposite modified membrane shows a higher porosity (60. 3 , ±,  , 2), a lower contact angle (55°, ), and its reduced structural parameter (S) to 0. 87 mm. The results revealed that the Al2O3/MA/CTA/CA nanocomposite modified membrane showed the highest water flux using 1 M of the KCl and NH4Cl (20 L/m2 h),followed by (NH4)2SO4 (19. 7 L/m2 h) and K2HPO4 (17. 6 L/m2 h) as draw solutions (DS) under the FO approach and using natural groundwater sample collected from Al-Zafer village, Sidi Barrani Area, north-western coast of Egypt with salinity of 8536 mg/L as feed solution (FS). It was revealed that the synthesized Al2O3/MA/CTA/CA nanocomposite modified membrane has great potential for application of FO process in brackish water desalination. The current cost per m2 of an Al2O3/MA/CTA/CA nanocomposite modified membrane is AU$ 32/m2 when compared with the commercial FO membrane (AU$ 188/m2).