Towards green membranes: preparation of cellulose acetate ultrafiltration membranes using methyl lactate as a biosolvent

Figures & data

Table 1 Environmental and human health risks of commonly used solvents. Ethyl and methyl lactates, as well as FAME, are presented for comparison purposes.

				Hansen solubility parameters (MPa^1/2)
Product	LD50 (g kg^− 1)	Vapour pressure (mmHg)	Risks	δd	δp	δh	d (solvent–CA) (MPa^1/2)
CA	>3.2 (OR)	−	None	16.0	7.2	13.5	−
Cyclohexane	12.7 (OR) 0.8 (OM)	96.8	Mutagen	16.8	0.0	0.2	15.14
DMSO	14.5 (OR)	0.42	Mutagen, tumorigenic	3.7	3.3	2.0	17.28
Acetone	5.8 (OR)	181	Highly flammable	15.5	10.4	7.0	7.26
Chloroform	1.2 (OR) 0.08 (OM)	158.3	Mutagen, teratogen	17.8	3.1	5.7	8.99
NMP	3.9 (OR) 8 (SR)	0.5 (25°C)	Irritant	18.0	12.3	7.2	8.35
FAME C8 to C18	>20 (OM)	2 (52°C)	None	17.0	4.5	5.6	17.05
Ethyl lactate	8.2 (OR) 2.5 (OM)	5 (30°C)	None	16.0	7.6	12.5	1.08
Methyl lactate	>5 (OR)	2.6	None	15.8	6.5	10.2	3.38
Notes: LD50, lethal dose 50% (INRS 2007). OR, oral rat; OM, oral mouse; SR, skin rabbit. Vapour pressure is presented at 20°C unless otherwise indicated. Hansen solubility parameters (Meireles et al. 1995) and distance from the solvent to CA in the Hansen 3D space.

Figure 1 Lab-scale equipment for mass transfer characterisation (permeability, PEG retention and MWCO determination).

Table 2 Molecular mass and hydrodynamic radius of the PEG used on the MWCO determination.

Molecular weight (kDa)	Hydrodynamic radius (nm)
0	0
10	4.6
20	6.7
35	9.2
100	16.4
200	24.2

Table 3 Membranes MWCO, pure water permeability and breaking pressure.

	MWCO
Membrane %w polymer, porogen	PEG (kDa)	r hyd (nm)	Pure water permeability at 20°C (litres h^− 1 m^− 2 bar^− 1)	Breaking pressure (bubble point) (bar)
16% CA, LiCl	35	9.2	177	4.5
20% CA, LiCl	20	6.7	23	3
20% CA, CaCl2	15	5.7	13	>5
Sterlitech CA UF CQ^a	20	6.7	10.2	< 4.9
a Data from the manufacturer.

Figure 2 MWCO determination: intrinsic retention vs. PEG molecular weight and hydrodynamic radius.

Figure 3 SEM image of the skin (a) and of the cross section (b) of the membrane obtained with 16% w/w CA, 6% LiCl and methyl lactate as a solvent.

Figure 4 SEM image of the skin (a) and of the cross section (b) of the membrane obtained with 20% w/w CA, 6% LiCl and methyl lactate as a solvent.

Figure 5 SEM image of the skin (a) and of the cross section (b) of the membrane obtained with 20% w/w CA, 6% CaCl₂ and methyl lactate as a solvent.

Figure 6 SEM image of the skin (a) and of the cross section (b) of commercial membrane Sterlitech CA UF CQ.