Nazila Dehbari

Neutralisation and compatibilisation effects on novel water-swellable rubber composites

A novel water-swellable rubber (WSR) composite, modified by a compatibiliser, was prepared by blending poly(dimethylsiloxane) rubber (PDMS) as a matrix and poly(acrylic acid) (PAA) partially neutralised by sodium hydroxide (NaOH) as a superabsorbent polymer. The addition of hydrophilic PAA into hydrophobic PDMS improved water swelling ability but without good durability, mainly due to the poor interfaces between PAA and PDMS. Meanwhile, the tensile properties of the WSR before and after swelling decreased dramatically. With NaOH added as the neutraliser for PAA or with aminopropyltriethoxysilane added as the compatibiliser for PDMS and PAA, water swelling ability and/or durability increased. However, when the compatibiliser and the neutraliser were added together, the water swelling ability and durability of the WSR composites further increased by virtue of the synergistic effects due to the increased interfacial cohesion between the PDMS and PAA.

In situ polymerized hyperbranched polymer reinforced poly(acrylic acid) hydrogels

Hydrogels have been extensively investigated for use in various applications. Poly acrylic acid (PAA) is a common example, which has been widely used due to its super hydrophilicity properties, biocompatibility and biodegradability characteristics. However its poor mechanical properties, which have been addressed in many research studies, are known as a drawback that limits its applications. So, enhancing PAA mechanical properties using a hyperbranched polymer (HB) is the key question to be addressed in this research. Investigations of the mechanical properties of the PAA-HB hydrogel revealed 130% improvement in the ultimate tensile strength, indicating a two times enhancement compared to that of PAA. Statistical analysis showed that the overall effect of introducing notches (with different depths) on the selected mechanical properties of both PAA and PAA-HB was significant. Mechanical characterization of PAA-HB networks showed that significant improvement in the mechanical properties was achieved as the capability of water uptake increased by 20%. Characterization of the physical properties confirmed that participation of HB may form a PAA based hybrid material with good swelling properties. Those findings are attributed to the supramolecular structure of the HB, which can introduce physical entanglement between the PAA network structure and increase the crystallinity of the final hydrogel as compared to those from the PAA hydrogel.

Polylactic Acid Based Rubber Composites and Nanocomposites

Polylactic acid (PLA) is one of the most promising polymers due to its biodegradability and other remarkable properties. It is relatively brittle, which can limit its usage in some applications. With the addition of elastomers, the toughening properties of PLA can increase greatly. However elastomers are commonly categorized as immiscible blends because of their poor adhesion between the dispersed phase and matrix. By enhancing the interaction between two component polymers, chemically or mechanically or by using a compatibilizer in the blend, the performance characteristics of the final product can be enhanced. This chapter deals with the different methods of producing PLA rubber based (nano) composite and its properties, the role of compatibilizers and various applications.

Effects of the processing methods on the gas permeability of PLA/Sepiolite thin films: solution casting versus thermo compression

A biodegradable poly-lactic acid (PLA)/Sepiolite nanocomposite films were prepared by the thermo-compression and solvent-casting methods, and barrier properties (water-vapor and gas barrier) were evaluated. By introducing sepiolite into PLA, the properties of nanocomposite films improved until a certain amount (1.5% wt). By increasing sepiolite loading, nanoparticles tented to agglomerate and gas permeability (GP) decreased. According to the results, the nanocomposite films prepared by the thermo-compression method were more brittle but strong due to the formation of more crystals; while solvent-casted films were more ductile due to the presence of solvent, which may act as a plasticizer, as evidenced by the results of the GP.