Application of post-consumer recycled high-impact polystyrene in the preparation of phase-inversion membranes for low-pressure membrane processes

Morphology and Thermodynamic Study of a Novel Composite Membrane from Waste Polystyrene/Slag: Experimental Investigation

The development of the membrane surface and cross-sectional morphology is pivotal in influencing the effectiveness of membrane separation. In this study, evaluating the separation rates between the solvent and nonsolvent in the casting solution and the related thermodynamic alteration analysis were illustrated. Additionally, the rheological variations were determined by measuring the viscosity of the resulting dope solutions, providing an initial estimation of the phase separation kinetics. Asymmetric polystyrene (PS)/slag composite membrane, incorporating slag waste as an inorganic additive, was developed. Dimethylformamide (DMF) was utilized as the solvent, and sodium dodecyl sulfate (SDS) was employed as an anionic surfactant to facilitate the casting process. A tertiary system diagram approach involving waste PS, DMF, and water introducing slag as an inorganic additive and SDS as a surfactant was attained to promote the separation of the solvent and nonsolvent in the casting solution. These novel composite mixtures exhibited increased thermodynamic instability within the coagulation bath, facilitating the rapid separation of solid membranes from the dope solutions and forming composite membranes with significantly increased porosity (exceeding a 20% increase) compared to that of plain waste materials. The composite membrane characteristics were assessed with the widely used poly(vinylidene difluoride) (PVDF) membrane, showing comparative features and performance when tested on a membrane distillation (MD) cell; it gave a flux of 1 kg/m2·h. These promising characteristics positioned this novel PS/slag composite membrane as a candidate for various water-related applications.

Synergistic Effects of Diatoms on Intumescent Flame Retardant High Impact Polystyrene System

In this work, aiming to improve the flame retardancy performance of high impact polystyrene (HIPS), HIPS compounds were synthesized with the addition of intumescent flame retardant (IFR: mass ratio of APP and PER was 3:1) and diatoms into HIPS matrix by melt blending method. It was found the IFR/diatoms system exhibited high flame retardant efficiency and catalytic carbonization effect to HIPS matrix in the burning process. The LOI value of HIPS-2 compound with the addition of 28 wt% IFR and 2 wt% diatoms was increased to 29.0% and passed V-0 rating. The value of PHRR for HIPS-2 compound is about 460.58 kW/m² compared with 937.22 kW/m² of pure HIPS and the value of THR for HIPS-2 compound is about 32.9 MJ/m² compared with 62.7 MJ/m² of pure HIPS, suggesting that the addition of IFR/diatoms system can decrease the values of PHRR and THR, which shows the synergistic effect between IFR and diatoms on reducing heat release. The 21.9% reduction in Av-EHC and 41.4% reduction in TSP seen on introducing an IFR/diatoms system indicates effective smoke suppression, which potentially would significantly reduce the death rate in real fire accidents. The TG-IR results indicated that the IFR/diatoms flame retardant system functioned in the gas phase to suppress the flame. The SEM images showed the char residue produced was more compact and continuous, which suggests that the IFR/diatoms flame retardant system exhibits barrier and catalytic effects to block heat transferring and promote char forming. The tensile strength and impact strength of HIPS-2 compound were 22.95 MPa and 2.63 KJ/m², respectively. The tensile strength and impact strength were increased by 34.13% and 19.55% compared with that of pure HIPS.

Effects of two-step cleaning sequences on foulant extraction from multibore ultrafiltration membranes in a pilot-scale membrane filtration system for surface water treatment

The cleaning efficiencies of fouled multibore ultrafiltration membrane (UF_MB) operated from a pilot-scale UF process for surface water treatment were systemically investigated according to the sequences of two different cleaning solutions. The experimental results decisively confirmed that HPI DOM and HPO DOM/multivalent ions complexation significantly resulted in the fouling formations on UF_MB due to their neutral charge characteristic. The basic cleaning agent effectively extracted the organic foulants attached on UF_MB, indicating that the type of cleaning agent was a critical factor influencing on the cleaning efficiency of fouled UF_MB. However, the cleaning sequence 1 (CS-1: 0.1 M NaOH >0.1 M HCl; the total DOC = 725.77 mgC∙m^-2; the total TN = 146.35 mgN∙m^-2, total inorganic contents = 132.62 mg m^-2) much more effectively extracted the foulants on the UF_MB surfaces than the cleaning sequence 2 (CS-2: 0.1 M HCl >0.1 M NaOH; the total DOC = 604.49 mgC∙m^-2; the total of TN = 121.79 mgN∙m^-2, total inorganic contents = 73.43 mg m^-2). The morphological results also clearly showed that the cleaned UF_MB surface using CS-1 were effectively recovered, as compared with those using CP-2. Overall, this study implied that the hydroxide ions from the basic cleaning agent promoted the infiltration of the acidic cleaning agent into the densely formed fouling layers on the UF_MB surfaces and demonstrated that the cleaning sequences strategy could significantly govern the restoration of UF_MB performance during the pilot-scale surface water treatment system operation.

Waste Reutilization in Polymeric Membrane Fabrication: A New Direction in Membranes for Separation

In parallel to the rapid growth in economic and social activities, there has been an undesirable increase in environmental degradation due to the massively produced and disposed waste. The need to manage waste in a more innovative manner has become an urgent matter. In response to the call for circular economy, some solid wastes can offer plenty of opportunities to be reutilized as raw materials for the fabrication of functional, high-value products. In the context of solid waste-derived polymeric membrane development, this strategy can pave a way to reduce the consumption of conventional feedstock for the production of synthetic polymers and simultaneously to dampen the negative environmental impacts resulting from the improper management of these solid wastes. The review aims to offer a platform for overviewing the potentials of reutilizing solid waste in liquid separation membrane fabrication by covering the important aspects, including waste pretreatment and raw material extraction, membrane fabrication and characterizations, as well as the separation performance evaluation of the resultant membranes. Three major types of waste-derived polymeric raw materials, namely keratin, cellulose, and plastics, are discussed based on the waste origins, limitations in the waste processing, and their conversion into polymeric membranes. With the promising material properties and viability of processing facilities, recycling and reutilization of waste resources for membrane fabrication are deemed to be a promising strategy that can bring about huge benefits in multiple ways, especially to make a step closer to sustainable and green membrane production.