Water–swellable Rubber Based on Hydroxyethylcellulose Grafted Polyacrylamide and Epoxidized Natural Rubber Blends

Abstract

The aim of research was to prepare water-swellable rubber (WSR) based on hydroxyethyl cellulose (HEC) grafted polyacrylamide (PAM) and epoxidized natural rubber (ENR) blends. Research was consisted mainly of 2 parts, 1) to synthesize of grafted copolymer by means of solution radical copolymerization. Superabsorbent polymers (SAPs) and superabsorbent polymers composites (SAPCs) were prepared successfully by solution graft copolymerization of polyacrylamide onto hydroxyethyl cellulose, using potassium persulfate (KPS) as an initiator, and N, N′-methylenebisacrylamide (MBA) as a crosslinker. The extent of grafting was evaluated from grafting yield percentage (%GY) and grafting efficiency percentage (%GE) at various HEC/AM ratios and determined optimal ratio. Influences of preparation parameters such as HEC/AM ratios, amount of initiator and crosslinker’s concentration, reaction temperature and time, and amount of filler on water swelling capacity of SAPs and SAPCs were also investigated. FTIR determination confirmed that the PAM was successfully grafted onto the HEC backbone, broad band for stretching vibration of –OH (HEC) at 3560-3320 cm-1 was changed into sharper with a shoulder band at 3195 cm-1 due to -NH stretching vibration in amide of grafted copolymer. The strong band of HEC at 1020 and 1059 cm-1 were disappeared due to -C-OH changes to -C-O-C- grafted copolymer. The swelling capacity of SAPs and SAPCs depended strongly on different parameters, and the maximum swelling capacity was 426 g/g and 538 g/g for the SAPs and SAPCs, respectively. 2) to compound the water-swellable rubber by mechanical blending of ENR and SAPC with curative package in an internal mixer (Brabender Plasticorder) at 40o C and rotor speed of 60 rpm. In this case, the SAPC was synthesized from SAP and bentonite clay. The WSRs with different epoxidation levels were investigated for first water swelling behaviors. It was found that the WSR with 50% mole epoxidation gave higher water absorbency, and lower in weight loss. Therefore, ENR-50 was chosen as the rubber matrix to prepare WSR by blending with SAPC at 0, 5, 10, 15, and 20 phr. The results found that water absorbency, weight loss and modulus increased with increasing SAPC contents, while the tensile strength, elongation at break and crosslink density decreased. Furthermore, a selective WSR prepared from ENR-50, SAPC, and curatives package have been compounded with polyvinyl alcohol (PVA) at 0, 0.5, 1, 5, 10 phr. The results found that increasing PVA content resulted in increased water absorbency but decreased weight loss. Nevertheless, the mechanical properties of the WSR was decreased with increasing PVA contents.