Preparation of microporous PVDF membrane via tips method using binary diluent of DPK and PG

Polyphenylene Sulfide-Based Membranes: Recent Progress and Future Perspectives

As a special engineering plastic, polyphenylene sulfide (PPS) can also be used to prepare membranes for membrane separation processes, adsorption, and catalytic and battery separators because of its unique properties, such as corrosion resistance, and chemical and thermal stability. Nowadays, many researchers have developed various types of PPS membranes, such as the PPS flat membrane, PPS microfiber membrane and PPS hollow fiber membrane, and have even achieved special functional modifications. In this review, the synthesis and modification of PPS resin, the formation of PPS membrane and the research progress of functional modification methods are systematically introduced, and the future perspective of PPS membrane is discussed.

On the Solubility and Stability of Polyvinylidene Fluoride

This literature review covers the solubility and processability of fluoropolymer polyvinylidine fluoride (PVDF). Fluoropolymers consist of a carbon backbone chain with multiple connected C-F bonds; they are typically nonreactive and nontoxic and have good thermal stability. Their processing, recycling and reuse are rapidly becoming more important to the circular economy as fluoropolymers find widespread application in diverse sectors including construction, automotive engineering and electronics. The partially fluorinated polymer PVDF is in strong demand in all of these areas; in addition to its desirable inertness, which is typical of most fluoropolymers, it also has a high dielectric constant and can be ferroelectric in some of its crystal phases. However, processing and reusing PVDF is a challenging task, and this is partly due to its limited solubility. This review begins with a discussion on the useful properties and applications of PVDF, followed by a discussion on the known solvents and diluents of PVDF and how it can be formed into membranes. Finally, we explore the limitations of PVDF's chemical and thermal stability, with a discussion on conditions under which it can degrade. Our aim is to provide a condensed overview that will be of use to both chemists and engineers who need to work with PVDF.

Non-Isothermal Crystallization Behavior of Poly(vinylidene fluoride) in Dialkyl Phthalate Diluents during Thermally Induced Phase Separation Process

The non-isothermal crystallization behavior of poly(vinylidene fluoride) (PVDF) in dialkyl phthalate diluents during the thermally induced phase separation (TIPS) process was investigated by differential scanning calorimetry (DSC) at various cooling rates. Dialkyl phthalates with different alkyl chain-length, namely dimethyl phthalate (DMP), diethyl phthalate (DEP) and dibutyl phthalate (DBP), were used as the diluent. The effects of alkyl chain-length of dialkyl phthalate and cooling rate on the non-isothermal crystallization behavior as implied by the Avrami analysis modified by Jeziorny and Mo’s analysis were determined. The values of half-time, t1/2, and the parameters Zc and F(t), which characterized the kinetics of non-isothermal crystallization, showed that the crystallization rate increased with the increase of the alkyl chain-length of dialkyl phthalate due to the lower compatibility between PVDF and dialkyl phthalate. Moreover, the alkyl chain-length of dialkyl phthalate also has a great impact on the compact spherulitic structure of PVDF membranes prepared from different PVDF/dialkyl phthalate blends. With the decrease of the alkyl chain-length of dialkyl phthalate, the number of spherulites increased and the size of spherulites became smaller. This research thus not only proves the effects of alkyl chain-length of dialkyl phthalate on the non-isothermal crystallization behavior of PVDF, but also provides a systematic strategy to evaluate a single diluent during the TIPS process.

Binary mixtures of semicrystalline polymers with low-molecular-mass compounds: thermal behaviour and phase structure

The results of phase equilibrium studies in mixtures of semicrystalline polymers with low-molecular-mass compounds are summarized and analyzed. A new classification of phase diagrams for such mixtures is proposed. Alternative points of view on the phase composition of semicrystalline polymers are presented. The phase structure evolution during the thermally induced phase separation of mixtures is monitored and the morphology of the forming capillary porous bodies as precursors of polymeric membranes is described. The general regularities concerning the influence of the nature of mixture components, polymer molecular mass, temperature scanning rate and other factors on the topology of phase diagrams are considered. Experimental methods used to construct the phase diagrams of mixtures and to study features of their phase structure are compared.

The bibliography includes 203 references.

Effects of Room Temperature Stretching and Annealing on the Crystallization Behavior and Performance of Polyvinylidene Fluoride Hollow Fiber Membranes

A treatment consisting of room temperature stretching and subsequent annealing was utilized to regulate the morphology and performance of polyvinylidene fluoride (PVDF) hollow fiber membranes. The effects of stretching ratios and stretching rates on the crystallization behavior, morphology, and performance of the PVDF membranes were investigated. The results showed that the treatment resulted in generation of the β crystalline phase PVDF and increased the crystallinity of the membrane materials. The treatment also brought about the orientation of the membrane pores along the stretching direction and led to an increase in the mean pore size of the membranes. In addition, as the stretching ratio increased, the tensile strength and permeation flux were improved while the elongation at break was depressed. However, compared to the stretching ratio, the stretching rate had less influence on the membrane structure and performance. In general, as the stretching ratio was 50% and the stretching rate was 20 mm/min, the tensile strength was increased by 36% to 7.47 MPa, and the pure water flux was as high as 776.28 L/(m²·h·0.1bar), while the mean pore size was not changed significantly. This research proved that the room temperature stretching and subsequent annealing was a simple but effective method for regulating the structure and the performance of the PVDF porous membranes.

Bicontinuous and cellular structure design of PVDF membranes by using binary solvents for the membrane distillation process

With excellent permeability as the foremost requirement for membranes used in the membrane distillation (MD) process, the thermally induced phase separation (TIPS) method is a promising approach for preparing porous membranes with a bicontinuous structure, which is identified as the best morphology for permeation. The structure design of membranes prepared by the TIPS process can be strengthened when a binary solvent is introduced in the casting solution. In this work, the determination principles for binary solvent were explicated in detail, and further employed for the selection of binary solvent for the fabrication of polyvinylidene fluoride (PVDF) membrane with different structures. By the TIPS approach, the porous PVDF hollow fiber membranes with cellular structure were generated by g-butyrolactone (GBL)/dioctyl phthalate (DOP) and GBL/dioctyl adipate (DOA) binary solvents, while the membrane with a bicontinuous structure was produced from GBL/dioctyl sebacate (DOS) binary solvent. The phase diagram was used to explain a feasible mechanism for the formation of the porous structures above. When the morphologies and properties of the membranes were characterized and compared, the membrane with a bicontinuous structure rather than a cellular structure was identified as the potential structure for MD processes with much higher tensile strength, narrower pore size distribution, higher MD flux and excellent long-term performance.

The membrane with bicontinuous structure rather than cellular structure was identified as the potential structure for MD processes with much higher tensile strength, narrower pore size distribution, higher MD flux and more excellent long-term performance.

Preparation of a polyphenylene sulfide membrane from a ternary polymer/solvent/non-solvent system by thermally induced phase separation

Polyphenylene sulfide (PPS) membranes were prepared via a thermally induced phase separation (TIPS) method.

Polymer Membranes with Vertically Oriented Pores Constructed by 2D Freezing at Ambient Temperature

Polymer membranes with well-controlled and vertically oriented pores are of great importance in the applications for water treatment and tissue engineering. On the basis of two-dimensional solvent freezing, we report environmentally friendly facile fabrication of such membranes from a broad spectrum of polymer resources including poly(vinylidene fluoride), poly(l-lactic acid), polyacrylonitrile, polystyrene, polysulfone and polypropylene. Dimethyl sulfone, diphenyl sulfone, and arachidic acid are selected as green solvents crystallized in the polymer matrices under two-dimensional temperature gradients induced by water at ambient temperature. Parallel Monte Carlo simulations of the lattice polymers demonstrate that the directional process is feasible for each polymer holding suitable interaction with a corresponding solvent. As a typical example of this approach, poly(vinylidene fluoride) membranes exhibit excellent tensile strength, high optical transparence, and outstanding separation performance for the mixtures of yeasts and lactobacilli.