دو ماهنامه علوم و تکنولوژی پلیمر
سال سی و ششم شماره 1 (پیاپی 183، فروردین و اردیبهشت 1402)

Today, the specialists’ attention on polyurethanes is increasing day by day due to easy synthesis, available raw materials, favorable mechanical properties, biocompatibility, and the possibility of providing different products, such as water-based polyurethanes, foams, hydrogels and glues. Chitosan is a natural polymer that is extracted from the deacetylation of chitin and contains glucosamine and N-acetyl glucosamine units. This non-toxic natural polymer has very useful properties such as antimicrobial activity, biocompatibility, biodegradability, and tissue repair and regeneration effects. One of the weaknesses of chitosan is its poor solubility and processability due to its strong intra- and intermolecular hydrogen bonding. Therefore, chitosan has been used mainly in modified form or in combination with other polymers in various applications. The combination of synthetic polymers with natural polymers is of particular importance because natural polymers such as chitosan can show some properties such as biocompatibility, biodegradability, low toxicity, high cell viability, and internal tissue growth; while the synthetic polymers have other characteristics such as favorable processing, mechanical and physical properties, and appropriate chemical and thermal stability. Recently, chitosan has been used in combination with polyurethanes to improve its mechanical properties, thermal stability, biodegradability, antimicrobial properties and biological activity. During these studies, products in various forms such as composite, elastomer, fiber, foam, scaffold, and hydrogel have been prepared for different applications. In this review, polyurethanes containing chitosan and their synthesis methods for various applications are discussed. The products prepared in these studies have been suggested for various applications such as antibacterial coating, wound dressing, tissue engineering scaffold, fabric modification, fibers, hydrogels and foams.

Today, reducing the use of volatile organic compounds is one of the most important issues for environmental protection. Since the 1950s, powder coatings have been widely considered in the surface coating field, especially pipelines, households, and office appliances, due to their environmental friendliness and excellent performance. These types of coatings are solid and they are applied to the surface in the form of powder using different methods such as electrostatic or fluidized bed and then they are cured by heat. In this study, a brief history of the development of powder coatings is described, and it is continued by full report on the types of powder coatings, their production methods and processes, and the research process, emphasizing the type and characteristics of the resins used in this industry. Considering the importance of powder resins in the formulation of powder coatings, the performance of various thermoplastic and thermosetting resins used in these powder coating systems, including polypropylene, polyethylene, poly(vinyl chloride), fluoropolyethylene, nylon, epoxy, polyester, polyurethane, acrylic, cellulose acetate butyrate, and recycled resins are compared. In addition, the method of application and film formation in electrostatic coatings and the factors affecting them are investigated comprehensively. Furthermore, some of the challenges and problems of this giant industry will be introduced in order to improve its quality and curing methods for to expand the applications. Finally, new technical approaches, aiming to save energy and produce more biocompatible powdered products, using infrared curing technology, curing by ultraviolet radiation, or the ability to coat sensitive-temperature surfaces by powder coating are described.

Hypothesis: 

Recently, preparation and investigation of hydrogel scaffolds in tissue engineering have gained increasing attentions owing to similarity of their characteristics to extracellular matrix of different tissues. Among different methods for hydrogel preparation, the use of ionizing radiation presents several advantages as it can occur without the need to add chemical agents and the final products can be irradiated to final form in the package, also simultaneously sterilized by irradiation during crosslinking. In this study, chemical modification with glycidylmethacrylate (GMA) as well as physical blending with poly(vinyl alcohol) (PVA) was investigated to prepare hydrogel scaffolds based on polysaccharides, gum tragacanth (GT) and carboxymethyl chitosan (NOCC) using electron beam irradiation.

For preparation of the hydrogels, first, GT and NOCC were functionalized with GMA. Afterwards, the blended solutions of these modified polymers and PVA were exposed to electron beam irradiation. Finally, the morphology, gel content, swelling behavior, compressive strength, rheological properties and biocompatibility of the hydrogels were investigated.

GMA-functionalized GT and NOCC in aqueous solution were crosslinked by electron beam irradiation. Blending of PVA with these modified polymers leads to the formation of an interpenetrating polymeric network (IPN) with enhanced compressive strength, storage modulus and swelling degree in comparison with the hydrogels prepared with unblended polymers. The gel content of the hydrogels varies between 65 to 98% as a function of polymer composition and irradiation dose. The hydrogels show viscoelastic behaviors in both compression and rheology analyses as well as excellent elastic recovery in cyclic compression analysis. The stress fracture of IPN hydrogels is found in the range of 1200-1414 kPa. The viability of MSCs, exposed to hydrogel extracts is above 85% after 24 and 72 h incubation. According to these results, the IPN hydrogels prepared in this study may be suggested as a promising candidate for further investigation, especially in cartilage tissue engineering.

Hypothesis: 

Superabsorbent polymers are modifiers that have broad applications. One of their applications is in concrete production industry. The use of these materials for supplying water to cement materials and their curing process has attracted the attention of researchers. Using SAPs in concrete is a valuable tool for areas where conventional curing is very difficult, such as extreme weather conditions that can lead to excessive evaporation and freezing. It also saves water.

Modified carbopol was prepared using poly(ethylene glycol) methyl ether methacrylate as a monomer with a molecular weight of 300 in amounts of 1, 2 and 3 g and with azobisisobutyronitrile (AIBN) as the initiator by ultrasound method. The properties of the prepared microgel and its effect on the properties of cement paste are investigated. The prepared microgel has been studied using FTIR analysis, scanning electron microscopy, particle size determination and swelling properties. In addition, the effect of prepared microgel on different properties of cement paste, such as rheology, compressive and flexural strength and hydration, is investigated.

The results of FTIR and microscopic images showed that the monomer was modified. According to the swelling results, it was observed that carbopol has no absorption and it is dissolved. After modification, the swelling and absorption properties are obtained. The swelling capacity in water and saline solution has increased first and then decreased with increasing monomer concentration. The resultant cement pastes show that the compressive strength of samples is decreased in the presence of modified carbopol. In addition, the strength of the cement paste prepared with commercial superabsorbent (polyacrylic acid sodium salt) has increased with the same water:cement ratio. The flexural strength is reduced in all samples compared to the reference. According to the results, the modified carbopol has increased the viscosity of the cement pastes. According to the XRD results, hydration and curing of samples with superabsorbent have completed within 28 days compared to the control cement. Therefore, it can be concluded that superabsorbents generally cause a delay in hydration, and besides the hydration of the superabsorbent-cement specimens is decreased by reducing the monomer.

Hypothesis: 

The aim of this research is to improve the fire behavior of thermoplastic polyurethane (TPU) using an intumescent flame retardant system (IFR) and nanosilica as a synergistic agent 

A three-component IFR system consisting of ammonium polyphosphate (APP), melamine polyphosphate (MPP), and pentaerythritol (PER) was added to TPU by melt mixing. The flammability of the TPU-IFR was evaluated by UL94 vertical burning test and the efficiency of the IFR was investigated by cone calorimeter test (CCT). A nanosilica as a synergist with low loading was added to the TPU-IFR composite, and fire properties were investigated. Thermal stability and char morphology were investigated by thermal analysis and scanning electron microscopy, respectively.

The results show that the IFR system is effective with a significant decrease of 62.6% in peak heat release rate (PHRR) and 58.3% in peak smoke production (pSPR). By incorporation of 0.5% (by wt) nanosilica into TPU-IFR, there are decreases in PHRR and pSPR by 75.0% and 79.2%, respectively, compared to the original TPU, while the dripping is removed. This has confirmed the effective synergism of nanosilica in enhancing the flame retardancy of TPU-IFR. Further, the amount of residual char has reached 31.2% and 58.9% for TPU-IFR and TPU-IFR-nanosilica, respectively, compared to 6.2% in a neat TPU. Both TPU composites have reached V0 grade in UL-94 test. FESEM shows an integrated compact char in IFR-TPU-nanosilica, while there are small holes in the char structure of IFR-TPU. Thermal analysis (TGA) has shown enhanced thermal stability in the two TPU composites by formation of a carbon layer as a thermal barrier during burning. This work introduces an efficient intumescent flame retardant system for improving the fire behavior of TPU which can significantly enhance the fire safety of TPU by a low loading of nanosilica as a synergist.

Hypothesis: 

In order to reduce the environmental pollution, it is an inevitable approach to replace petroleum polymers with biodegradable materials. Poly(lactic acid) (PLA) is one of the suitable alternatives for synthetic polymers, due to its biodegradability and biocompatibility as well as high tensile strength, but the application of PLA faces limitations due to its brittleness.

In this research, blends of PLA containing 25% (by wt) poly(butylene adipate-co-terephthalate) (PBAT), a biodegradable and flexible polymer, were prepared. Nanocomposites containing 1 and 3 phr nanoclay (Cloisite 20A) were prepared at the same time. The compatibilizing effect of chain extender (CE) (ADR 4368) (0.5 phr) for this system was investigated. The rheological, morphological, mechanical and thermal properties of all samples have been studied. 

Rheology results show a significant increase in the storage modulus and complex viscosity of samples containing both nanoclay and chain extender. SEM images illustrate droplet-matrix morphology of all samples. It is shown that the size of PBAT dispersed phase in nanocomposites is decreased, especially in the sample containing 3 phr nanoclay and 0.5 phr chain extender (2.54 to 1.15 mm). The results of mechanical tests show that all nanocomposites, specially samples containing both nanoclay and chain extender have made a significant improvement in all mechanical properties, in comparison to a neat PLA (about 13.6 times in elongation-at-break and more than twice in impact strength for nanocomposite containing 3 phr nanoclay and 0.5 phr chain extender). These findings confirm the results of rheology and morphology and reveal a synergistic effect of using nanoclay and chain extender for the compatibilization of the system. The XRD analysis reveals an increase in the distance of nanoclay plates, which is due to diffusion of polymer chains into its layers. Finally, the DSC analysis shows that the crystallinity of the samples increases in the presence of nanoclay particles.