PREPARATION OF MICROPOROUS ULTRA HIGH MOLECULAR WEIGHT POLYETHYLENE (UHMWPE) BY THERMALLY INDUCED PHASE SEPARATION OF A UHMWPE/LIQUID PARAFFIN MIXTURE

Ultra-high molecular weight polyethylene (UHMWPE) with a microporous structure was prepared via thermally induced phase separation (TIPS).Liquid paraffin (LP) was used as a diluent in the preparation of microporous UHMWPE. Small angle laser light scattering (SALLS) and differential scanning calorimetry (DSC) were used to determine the phase separation temperatures,i.e.the cloud points and the dynamic crystallization temperatures,respectively.It was found that the cloudI points were coincident with the cr...

Fabrication of poly(vinylidene fluoride) membrane via thermally induced phase separation using ionic liquid as green diluent

Ionic liquid(IL),1-butyl-3-methylimidazolium hexafluorophosphate([BMIM]PF6)as a new and environmentally friendly diluent was introduced to prepare poly(vinylidene fluoride)(PVDF)membranes via thermally induced phase separation(TIPS).Phase diagram of PVDF/[BMIM]PF6 was measured.The effects of polymer concentration and quenching temperature on the morphologies,properties,and performances of the PVDF membranes were investigated.When the polymer concentration was 15 wt%,the pure water flux of the fabricated membrane was up to nearly 2000 L·m-2·h-1,along with adequate mechanical strength.With the increasing of PVDF concentration and quenching temperature,mean pore size and water permeability of the membrane decreased.SEM results showed that PVDF membranes manufactured by ionic liquid(BMIm PF6)presented spherulite structure.And the PVDF membranes were represented asβphase by XRD and FTIR characterization.It provides a new way to prepare PVDF membranes with piezoelectric properties.

Fabrication of Poly(vinylidene fluoride) /Polysulfone Flat Blend Membranes via Thermally Induced Phase Separation Process for Water Treatment

Poly(vinylidene fluoride) /polysulfone(PVDF/PSF) flat blend membrane was prepared via thermally induced phase separation(TIPS) technique.The membrane formation mechanism and membrane structure were investigated and the effects of PSF/PVDF weight ratio on morphology,crystallinity,porosity,and mechanical properties of the membrane were discussed.The relationship between membrane structure and performances,such as pure water flux and the rejection of carbonic black,was also discussed.It was found that solid-liquid(S-L) phase separation occurred for the PVDF/PSF/diluent system.The addition of PSF influences structure and crystallinity of the membrane,which in turn influences mechanical properties and performances of the membrane.The results reveal that it is possible to obtain network structure via S-L phase separation by blending the polymer,which has a partial compatibility with PVDF.

Polysulfone Membranes via Thermally Induced Phase Separation

Polysulfone(PSF) membranes have gained great attention in the fields of ultrafiltration, microfiltration, and thin film composite membranes for nanofiltration or reverse osmosis. For the first time, it is proposed to fabricate PSF membranes via thermally induced phase separation(TIPS) process using diphenyl sulfone(DPSO2) and polyethylene glycol(PEG) as mixed diluent. DPSO2 is chosen as a crystallizable diluent, while PEG isconsidered in terms of molecular weight(M_w) and dosage. We systematically investigate the interactions between PSF, DPSO2 and PEG based on thesimulation calculations and solubility parameter theory. It is inferred that DPSO2 has an excellent compatibility with PSF, and the addition of PEG results in the ternary system thermodynamically less stable and then facilitates its liquid-liquid(L-L) phase separation.SEM images indicate that cellular-like pores are obvious throughout the membrane when the PEG content in the mixed diluent is 25wt%-35 wt%. We can facilely manipulate the pore size, water flux and mechanical properties of PSF membranes with the dosage of PEG-200, the M_wof PEG or the cooling rate. The successful application of TIPS can provide a new approach for structure manipulation and performance enhancement of PSF membranes.

Poly(vinylidene fluoride-co-hexafluoro propylene) membranes prepared via thermally induced phase separation and application in direct contact membrane distillation

A non-toxic and environmentally safe diluent,acetyl tributyl citrate,was employed to prepare poly(vinylidene fluoride)-co-hexafluoropropylene membranes via thermally induced phase separation.Effects of the polymer concentration on the phase diagram,membrane morphology,hydrophobicity,pore size,porosity and mechanical properties(tensile stress and elongation at break)were investigated.The results showed that the pore size and porosity tended to decrease with increasing polymer concentration,whereas the contact angle,liquid entry pressure and mechanical properties showed the opposite trend.In direct contact membrane distillation operation with 3.5 wt-%sodium chloride solution as the feed solution,the prepared membranes performed high salt rejection(>99.9%).Furthermore,the prepared membranes retained excellent performance in long-term stability tests regarding the permeate flux and salt rejection. ne distillation.

Enhancement of solvent uptake in porous PVDF nanofibers derived by a water-mediated electrospinning technique

The effect of a N,N-dimethylformamide(DMF)/acetone solvent system(3:7,4:6,5:5,6:4,7:3)and spinning medium(air and water)on the membrane morphology and the structure-property relationship were investigated.A facile method was optimized to generate a porous,polymer-fiber membrane via the combinative effect of electrospinning and thermally inducing phase separation of the DMF/acetone(4:6)solvent system in a water medium.The attenuated total reflection(ATR)-Fourier transform infrared(FTIR)results showed an increased b-phase compared to the pristine poly(vinylidene fluoride)(PVDF).The XRD and DSC results further confirmed that the co-existing a-and b-phases in the pristine PVDF were converted into a unique b-phase in the electrospun membranes.In addition,the solvent uptake percentage of the DMF/acetone(4:6)solvent system in a water medium(540)is much greater than that in an air medium(320),and over two times better than that of commercial polyethylene(PE)membranes(190).Similarly,the discharge capacity of the PVDF membrane separator prepared with the DMF/acetone(4:6)solvent system in a water medium is higher than that of the air medium.This enhancement of solvent uptake might be due to the interconnected porous morphology present in the water medium.