Hydrolytic degradation of copolymers based on l-lactic acid and bis-2-hydroxyethyl terephthalate

Sustainable utilization of chemically depolymerized polyethylene terephthalate (PET) waste to enhance sand-bentonite clay liners

Polyethene terephthalate (PET) waste poses major environmental harm which can be minimized by reusing it in clay soil stabilization. In general, various polymers are known to reduce hydraulic conductivity and increase the shear strength of clays. However, the application of the effect of a chemically depolymerized form of PET, i.e., Bis (2-Hydroxyethyl) terephthalate (BHET) has not been performed as an additive in Compacted Clay Liners (CCLs) for landfills. This research focuses on the effect of the air curing period (1 and 28 days) on the hydromechanical behavior of BHET-treated SBM (0, 1, 2, 3, and 4 % by dry weight). Results from One Dimensional Consolidation tests showed that an increase in BHET content reduced both compressibility and hydraulic conductivity of SBM due to pore clogging mechanism of swollen BHET hydrogel, however, hydraulic conductivity reduced over 28 days of curing due to loss in re-swelling availability of the hydrogel, thereby allowing less tortuous paths to flow. Results from Consolidated-Drained Direct Shear tests showed that for 1 and 28-days curing, BHET treatment to SBM increased the cohesion (c') due to strong polymer interparticle bridging, however, polymer coating over the sand grains causes a reduction in its surface roughness to decrease the frictional angle (ϕ'). SEM (Scanning Electron Microscopy) and EDX (Energy-dispersive X-ray spectroscopy) analysis on BHET-treated specimens support the flocculation of bentonite, polymer bridging of sand and clay-sand polymer links. A significant Pb²⁺ removal capacity was also observed with BHET-treated SBM from the batch tests. FTIR (Fourier Transform Infrared Spectroscopy) analysis on batch sorption specimens confirms the role of the carbonyl groups (C = O) and hydroxyl groups (OH) present in the BHET structure indicating the possibility to adsorb Pb²⁺. The findings of the study suggested that a mechanism of interaction exists between sand-bentonite and BHET polymer and it can be adopted in CCLs design.

Hydrolytic degradation behaviour of sucrose palmitate reinforced poly(lactic acid) nanocomposites

This work discusses the influence of novel biofiller, "sucrose palmitate" (SP) on the hydrolytic degradation behavior of poly(lactic acid) (PLA) nanocomposites. The influence of temperature and pH of the solution on the hydrolytic degradation behavior of PLA and PLA-SP nanocomposites was investigated. The variation in the crystallinity of PLA and PLA composites subjected to the hydrolytic degradation process is verified by XRD and DSC analysis. The morphological changes that occurred during the degradation process are observed by scanning electron microscopy (SEM). Thermo-gravimetric analysis confirms the loss of thermal stability of the neat PLA as well as composites after hydrolytic degradation process. Transparency measurements support the enhancement in opacity of both the PLA and PLA-SP nanocomposites with progress in hydrolytic degradation period.

Thermosensitivity and release from poly N-isopropylacrylamide-polylactide copolymers

A series of thermoresponsive-co-biodegradable polymers, containing varying molar ratios of N-isopropylacrylamide (NIPA) and poly-lactic acid diacrylate macromer (PLAM) were prepared and characterised. Chemical structures were confirmed by nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR). The hydrogels were thermoresponsive, exhibiting an increase in the lower critical solution temperature (LCST) the higher the percent of PLAM present. Swelling properties were dependant on both temperature and PLAM content. The degradation behaviour of the three-dimensional polymeric networks formed was dependent on both structural (mesh size, molecular weight distribution, composition) and environmental parameters (temperature). Swelling and in vitro biodegradation-induced morphological structural changes were examined using scanning electron microscopy (SEM). A greater rate of degradation and disruption to the porous network could be seen with increasing lactide content. Degradation was faster below the LCST, demonstrated by FTIR, pH decrease and acid release, consistent with the increased hydrophilicity of the network. The release profiles of the model drug indomethacin (IDM), from these thermoresponsive-co-biodegradable polymers, were found to be dependant on copolymer composition, drug loading and temperature, more rapid release occurring below the LCST.