Nanoclay Dispersion and its Effect on Properties of Waterborne Polyurethanes

In recent years, waterborne polyurethanes as in coatings and adhesives formulations have attracted considerable attention because they are non-toxic, non-flammable and friendly to environment. Besides environmental management, the flexibility, low temperature property, high tensile strength, good adhesion and improved rheological property are specific properties of waterborne polyurethanes. Also low production cost of water borne polyurethanes over solvent-borne polyurethanes is also a reason for their applications. However, these materials have some defects such as weak water resistance and low adhesion in the moisture environment due to sensitivity of their hydrophilic ionic bonds, ether groups, urethane and ester groups to hydrolysis which need to be improved. Also, low heat resistance of these materials is due to a relatively low crystalline melting point or glass transition temperature of hard segments. One of the ways to solve this problem and improve its properties for different applications is the addition of inorganic fillers especially nano-sized layered silicates within polyurethane matrix. In this way water resistance, heat resistance, mechanical properties and modulus increase simultaneously. In this research, waterborne polyurethane nanocomposites with PTMG polyol, IPDI, DMPA (internal emulsifier), TEA (neutralizer) and 1, 3 and 5weight % of Cloisite 30B as reinforcement were synthesized and characterized. Polarity of the samples was investigated by contact angle test and dispersion of nano particles in the samples was characterized by X-Ray and TEM, Thermal properties and dynamic mechanical properties were measured by TGA and DMTA, respectively. The results showed that incorporation of clay into polyurethanes did reduce water absorption and increased heat resistance, modulus, particle size and contact angle.In recent years, waterborne polyurethanes including coatings and adhesives have attracted considerable attention because they are non-toxic, non-flammable and friendly to environment. Besides environmental management, flexibility, low temperature property, high tensile strength good adhesion and improved rheological property are specific evidence of waterborne polyurethanes. Also low production cost of water borne polyurethane over solvent-borne polyurethanes is also a reason for their applications. However, these materials have some defects such as weak water resistance and low adhesion in the moisture environment due to sensitivity of their hydrophilic ioned bonds, ether groups, urethane groups and ester groups to hydrolysis which are needed to be improved. Also, low heat resistance of these materials is due to relatively low crystalline melting point or glass transition temperature of hard segments. One of the ways to solve this problem and improve its properties for different application is the addition of inorganic fillers especially nanosized layered silicates within polyurethane matrix.  In this way water resistance, heat resistance, mechanical properties and modulus increase. In this research, waterborne polyurethane nanocomposites with PTMG polyol, IPDI, DMPA (internal emulsifier), TEA (neutralizer) and 1, 3 and 5weight % of cloisite 30B as reinforcement were synthesized and characterized. Polarity of the samples was investigated by Contact angle test, dispersion of nano particles in the samples were characterized by X-Ray and TEM, Thermal properties and dynamic mechanical properties were measured by TGA and DMTA respectively. Results showed that incorporation of clay into polyurethane samples caused the reduction of water absorption, increasing of heat resistance, modulus, particle size and contact angle

Cellulose and its derivatives: towards biomedical applications

© 2021, The Author(s).Cellulose is the most abundant polysaccharide on Earth. It can be obtained from a vast number of sources, e.g. cell walls of wood and plants, some species of bacteria, and algae, as well as tunicates, which are the only known cellulose-containing animals. This inherent abundance naturally paves the way for discovering new applications for this versatile material. This review provides an extensive survey on cellulose and its derivatives, their structural and biochemical properties, with an overview of applications in tissue engineering, wound dressing, and drug delivery systems. Based on the available means of selecting the physical features, dimensions, and shapes, cellulose exists in the morphological forms of fiber, microfibril/nanofibril, and micro/nanocrystalline cellulose. These different cellulosic particle types arise due to the inherent diversity among the source of organic materials or due to the specific conditions of biosynthesis and processing that determine the consequent geometry and dimension of cellulosic particles. These different cellulosic particles, as building blocks, produce materials of different microstructures and properties, which are needed for numerous biomedical applications. Despite having great potential for applications in various fields, the extensive use of cellulose has been mainly limited to industrial use, with less early interest towards the biomedical field. Therefore, this review highlights recent developments in the preparation methods of cellulose and its derivatives that create novel properties benefiting appropriate biomedical applications