**5.1 PEG used as pore-forming additive**

In the early 1990s, PEG was used as pore-forming additive to fabricate microporous polyvinylidene fluoride (PVDF) membrane for MD of wastewater discharged from the taurine production [33]. The effects of a series of PEG 400, 1000, 1540, 2000, and 6000 on the pore structure and permeate performance of poly(vinylidene fluoride-co-hexafluoropropylene) (F2.6) flat-sheet membranes were investigated by evaluating average pore radius, porosity, and morphology, and the membranes reached better higher distilled flux than the PVDF membrane during the DCMD test [34]. Dayanandan et al. studied the influence of the various additions of PEG (0–4 wt%) in the coagulation bath composition during the preparation of PVDF membranes, and they found that the bath-based MD membrane with 4 wt% PEG had relative superior overall performance than other membranes based on various evaluations of elongation-at-break, tensile strength, liquid entry pressure, hydrophobicity, porosity, and water flux [35]. Combined effects of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and the concentrations of the additive PEG 10000 were studied by using a statistical approach, and the optimized membrane achieved salt rejection of 99.5% in the DCMD of 0.1 M NaCl solution at 65°C [36]. Two pore-forming additives PEG and LiCl both at 4 wt% were used in the fabrication of hydrophobic flat sheet and hollow fiber PVDF and PVDF-co-chlorotrifluoroethylene (PVDF-CTFE) membranes for membrane distillation [37, 38]. The effect of mass ratio of PEG and LiCl was further investigated for making PVDF-CTFE membranes for MD [39]. Recently, more effective additives such as organic acids, LiCl, MgCl2, and LiCl/H2O mixtures along with PEG were investigated in the fabrication of flatsheet hydrophobic PVDF-CTFE membranes used for MD [38]. Hou et al. prepared hydrophobic PVDF flat-sheet membranes for DCMD by using various non-solvent additives such as acetone, phosphoric acid, glycerine, LiCl, and PEG 400 [40]. They found that the membrane fabricated with 5 wt% acetone and 3 wt% phosphoric acid exhibited the highest water flux among the various fabricated membranes and showed great performance stability in the 240 h desalination of synthetic seawater. There exist more novel additives, such as calcium carbonate nanoparticles and TamiSolve® NxG along with PEG and LiCl, applied to the fabrication of hydrophobic membranes for MD [41, 42].

During the fabrication of microporous PVDF hollow fiber membranes, two non-solvent additives PEG 400/1500 and LiCl were added to the feed N,Ndimethylacetamide (DMAc) solution containing PVDF powder [43–46]. The experiment factors such as dope extrusion rate, take-up speed, air-gap concentration of polymer and additives, and bore liquid temperature were investigated in the membrane fabrication through a dry-jet wet phase inversion process, and the obtained membranes were suitable for DCMD than VMD. Recently, Zhang et al. further discovered the regulatory role of coagulation bath temperature during PVDF membrane fabrication when PEG 400 and triethyl phosphate were used [47]. In the fabrication process of PVDF hollow fiber membranes via complex thermally integrated phase separation at 80°C for MD, triethylphosphate (TEP) and PEG 200 were used as weak solvent and weak bore fluid, respectively [48]. PEG 6000 was used to fabricate hollow fiber MD membranes by Garcia-Payo et al. [49, 50]. They also dissolved PEG 10000 in DMAc to prepare PVDF-HFP hollow fiber membranes, and the optimized membrane had high permeate flux and salt rejection [51, 52]. Similarly, the concentration effects of PEG 600 (0–20 wt%) on the performance of PVDF-HFP membranes for MD were also investigated, and the suitable range of 5–20 wt% was found for fabricating hollow fiber MD membranes with acceptable

**63**

**Table 1.**

**Membrane type**

FO Jeffamine

MD PEG 2000

MD PEG 200 and

ED-2003

and 10000

400

*Association of Polyethylene Glycol Solubility with Emerging Membrane Technologies, Wastewater…*

performance [53]. Recently, Wang et al. developed hydrophobic flat sheet and hollow fiber membranes PVDF and PVDF-CTFE for DCMD using PEG 400 and LiCl

In order to explore new applications of microfiltration (MF) membrane in MD, a hydrophobic PVDF membrane with pore size of 0.2 μm and thickness of 125 μm was surface-casted with hydrophilic polymer gel made from a polymer solution containing 20% PEG and 3% polyvinyl alcohol (PVA) [15]. The modified membrane exhibited the excellent abilities to keep high constant flux at high salt concentration of 20–25% NaCl for a long time MD running and to prohibit the wetting problem when testing with 25% ethanol even. Recently, Zuo and Wang modified a PVDF membrane with a pore size of 0.22 μm and thickness of 125 μm by grafting PEG and depositing TiO2 micro-balloonshaped particles on the membrane surface [16]. In the desalination test of synthetic seawater containing 0.01 wt% of mineral oil over the 1-day operation, the fabricated membrane with a highly hydrophilic surface kept a stable water flux with negligible fouling and wetting. Later, Meng et al. investigated the effect of templating agents, such as PEG 1000, Pluronics F-127, Wacker IM-22, and cetyltrimethylammonium bromide, on the properties and MD performance of TiO2-coated PVDF membranes [55]. Their MD membrane templated with PEG achieved the most promising overall performance of water flux, salt rejection, and extended operation time due to the optimum reduction of pore wetting induced by the templating agent PEG. They further developed superhydrophobic nanocomposite PVDF membranes for DCMD by modifying the conventional PVDF membrane with a pore size of 0.45 μm, and a dip coating of sol-gel containing PEG was used after a TiO2 and fluro-silane coating in the modification [56].

**6. PEG-assisted membranes in wastewater treatment and desalination**

As emerging membrane technologies, FO and MD have received increased attentions for wastewater treatment and desalination [14, 57–60]. FO takes some

FO PEGDE Synthetic wastewater Alleviation of flux reduction

Synthetic secondary wastewater

MD PEG 2000 Taurine wastewater Nonvolatile solute can be

MD PEG 1000 10% NaCl Recovery ratio: about 68% [55]

Formulated seawater Flux: 61.6 kg/m2

MD PEG 1500 3.5% NaCl Flux: 40.5 kg/m2

*PEG-assisted FO and MD membranes used in wastewater treatment and desalination.*

**PEG Wastewater/desalination Performance improvement Ref.**

NaCI solution Remain 91% flux for 3.5 NaCl;

by 50%

Complete removal of organic foulant with NaCl solution

concentrated by MD

almost unchanged flux for 20% NaCl

rejection: 99.99% at 81.8°C

rejection: 99.99% at 71°C

h; NaCl

h; NaCl

[28]

[29]

[33]

[15]

[45]

[48]

**5.2 PEG applied to surface modification of MD membrane**

*DOI: http://dx.doi.org/10.5772/intechopen.89060*

as the additives [54].

*Association of Polyethylene Glycol Solubility with Emerging Membrane Technologies, Wastewater… DOI: http://dx.doi.org/10.5772/intechopen.89060*

performance [53]. Recently, Wang et al. developed hydrophobic flat sheet and hollow fiber membranes PVDF and PVDF-CTFE for DCMD using PEG 400 and LiCl as the additives [54].
