Preparation And Properties Of Interpenetrating Network Hydrogels Based On Polyacrylamide

Hydrogels are a kind of functional polymer maretials integrating water absorption andretention, controlled-release, and soft handle together. They have been widely used inhygienic production, agriculture, biomedical engineering and other fields due to their uniqueproperties, such as high sretchability, water absorption and retention, as well as soft tissusestate. However, many hydrogels are generally brittle and fragile with poor formability. Inorder to improve hydrogel strength and formability, ionic crosslink and intermolecularhydrogen bond were assisted in enhancing mechanical strength respectively through one-potinterpenetrating based on the IPN reinforcement principle of interlock structure.PAM hydrogels with different initiator dosages, synthetic time, temperature, andcrosslinker concentrations were prepared using N,N’-methylenebisacrylamide (MBA) ascrosslinker and ammonium persulfate (APS) as initiator. And the equilibrium swelling ratio(ESR) was used to evaluate the network structure of hydrogel. The results show that reactionunder60°C for2h with0.6%mol L-1APS and0.05mol%MBA, the prepared PAMhydrogel show better network structure, presenting ESR of24. Through tensile test of PAMhydrogels under various MBA concentrations, it is concluded that the tensile strengthdecreases as MBA increasing, which demonstrates that flexibility mainly dominates in thestrength of chemical crosslinked PAM hydrogels.The ionically crosslinked network was introduced into hydrogel network through IPNtechnique for enhancing hydrogel strength. Covalent/ionic crosslinked PAM/SA IPN hydrogelwas produced firstly with linear SA interpenetrated in PAM for formation of PAM/SAsemi-IPN, and then ionically crosslink SA with CaCl2. PAM/SA hydrogel can form differentshapes through mould adjustment, presenting superior formability. TGA results confirm thatthe heat resistance of PAM/SA IPN hydrogel is improved as compared to that of theindividual component. Swelling kinetics of PAM/SA semi-IPN and PAM/SA IPN hydrogelswith either different MBA content or SA dosages indicate that the swelling rate of PAM/SAsemi-IPN hydrogel depends on the relaxation of polymer chains, belonging to non-Fick mode.On the contrary, the swelling behavior of PAM/SA IPN hydrogel belongs to Fick mode whichrelies on solvent diffusion. The effects of composition and ionic crosslinking on mechanicaland swelling properties of PAM/SA semi-IPN and PAM/SA IPN were discussed. The resultsshow that with the increase of crosslinker content, ESR of both PAM/SA semi-IPN andPAM/SA IPN hydrogels firstly increase to a maximum value and then decrease. The ESRpresents an increasing trend for PAM/SA semi-IPN hydrogel with the augment of SA dosage,while reveals an opposite trend for PAM/SA IPN hydrogel. PAM2-0.05/SA20IPN hydrogelcomposed of0.05mol%crosslinker,20wt%SA which treated using2wt%CaCl2for24hpresents excellent mechanical properties, showing tensile strength of1.96MPa which iscomparable to conventional DN hydrogels. Loosely chemically crosslinked PAM coupledwith tightly ionically crosslinked SA synergistically enhance mechanical strength of PAM/SAIPN hydrogel.Intermolecular hydrogen bond was designed to introduce into hydrogel network based on IPN technique for further enhancing hydrogel strength. The PAM/PVP semi-IPN hydrogelwas synthesized using one-pot IPN technique with PVP interpenetrated in flexible PAMnetwork. The swelling and mechanical properties of PAM/PVP semi-IPN hydrogel werediscussed. The swelling rates of PAM/PVP semi-IPN hydrogels under different monomercontent, crosslinker concentration and PVP dosage depend on solvent diffusion throughanalyzing swelling behavior, which belongs to Fick mode. Monomer content, crosslinkerconcentration, PVP dosage and water content were varied to investigate the effects onphysical and mechanical properties of PAM/PVP semi-IPN hydrogel. The results show thatthe ESR declines with the increase of monomer content, crosslinker concentration and PVPdosage, respectively. The tensile experiments show that tensile strength of hydrogel isimproved through introducing PVP into PAM. The mechanical properties present better inpresence of AM6mol L-1with n(MBA)/n(AM) and m(PVP)/m(AM) of1.67×10-4and7.51%respectively, showing tensile strength of1.84MPa and elongation of3322%. With theincrease of water content in hydrogel, both tensile strength and elongation are reduced. Theresults of FTIR, TGA coupled with hydrogel appearance demonstrate that hydrogen bondoccurs between PAM and PVP. The mechanical strength of hydrogels were dramaticallyimproved with loosely chemically crosslinked PAM under hydrogen bond with PVP.Temperature-sensitve P(NIPAM-co-AM) hydrogel was prepared by introducing AM intoNIPAM. With the augment of hydrophilic AM, the swelling ratio, water retention and LCSTwere increased, leading to lower temperature-sensitivity. The proportion of AM/NIPAM is themost important factor of hydrogel temperature-sensitivity. According to DSC, when w(AM)increases from2%to10%, the LCST of P(NIPAM-co-AM) hydrogel increases from38.61°Cto57.95°C. As crosslinker concentration accelerates, swelling ratio of P(NIPAM-co-AM)decreases, but water retention and mechanical strength are improved, and the LCST remainsconstant. P(NIPAM-co-AM)/SA IPN and P(NIPAM-co-AM)/PVP semi-IPN hydrogelsobtained by introducing inoically crosslinked SA and PVP into P(NIPAM-co-AM)respectively which still exhibit temperature-sensitivity show better mechanical strength thanP(NIPAM-co-AM) and consistent LCST with P(NIPAM-co-AM).