At present, water pollution and water
shortage have seriously threatened people's life safety. For a long time, the
treatment of water pollution has been the focus of environmental protection. Membrane technology has been one of the
mainstream treatment methods because of its green environmental protection,
sustainability, rapid and efficient separation process and other advantages,
and has achieved good results. PTFE microporous membrane material has
been concerned and studied by international scholars for its excellent chemical
resistance, high porosity and good mechanical properties. However, PTFE
microporous membrane has the characteristics of low surface energy and high
hydrophobicity, which greatly limits its application in the field of water
treatment. Therefore, improving the hydrophilicity of PTFE microporous membrane
has become an important research direction.
In this paper, polyvinyl alcohol (PVA) and
chitosan or oxycarboxymethyl chitosan were used as hydrophilic agents.
Different crosslinking agents were used to wrap a hydrogel hydrophilic coating
on PTFE microporous membrane fiber through crosslinking reaction, so as to
realize the hydrophilic modification of PTFE microporous membrane.
Specifically, the following two parts of
the study were carried out:
(1)
polyvinyl alcohol (PVA) with
good hydrophilic property and chitosan (CS) with good antibacterial property
were selected as materials to modify PTFE microporous membrane by combining
hydrogel coating formed by epichlorohydrin crosslinking with SiO2 nanoparticles
in situ under alkaline conditions.
The experimental results showed that the fiber surface of
modified PTFE microporous film was coated with a layer of hydrogel, and the
hydrogel coating attached a large number of solid particles to the node, which
improved the surface roughness and reduced the average pore diameter and
porosity slightly. Hydroxyl and amino groups appeared on the surface of
modified film. New elements N,O,Si
appeared on the surface of modified membrane. With the increase of PVA solution
concentration, the water flux of the modified membrane first increases and then
decreases, and the contact Angle of the membrane surface first decreases and
then tends to be stable. With the increase of reaction time, the water flux of
the modified membrane first increased and then decreased. With the increase of
reaction temperature, the water flux of the modified membrane increases first
and then decreases, and the contact Angle of the membrane surface decreases
first and then increases. The optimal reaction conditions are :PVA solution
concentration is 1wt%,CS solution concentration is 0.3wt%, the mass ratio of CS
solution to PVA solution is 1:1. The reaction time is 6h, the reaction
temperature is 40℃, the reaction pH is 12, and the water dilution ratio in the
secondary treatment is 45 times (PBA:SiO2=1:2.5).
The contact Angle of hydrophilic modified PTFEmicroporous membrane decreased from 136° to 48°, and the pure water flux
reached 3172L·m-2·h-1.The experimental results of oil in water emulsion
separation of hydrophilic modified PTFE microporous membrane show that the
hydrophilic modified PTFE microporous membrane has good anti-oil properties and
oil retention rate of 97%.The physical and chemical stability of hydrophilic
PTFE microporous membrane shows that the hydrophilic PTFE microporous membrane
has good acid resistance and washing resistance.
(2) PTFE microporous membrane was modified with
polyvinyl alcohol (PVA) and oxygen carboxymethyl chitosan (OCMCS) by
crosslinking with glutaraldehyde under acidic conditions.
The results showed that the fiber surface of PTFE microporous
membrane was covered with a hydrogel coating,
and the surface of PTFE microporous membrane still retained the original
three-dimensional network structure. Hydrophilic hydroxyl and amino groups
appeared on the surface of PTFE microporous membrane. With the increase
of PVA content in the reaction solution, the water flux of the modified
membrane increases first and then decreases, and the contact Angle decreases
first and then increases. With the increase of reaction temperature, the water
flux of modified membrane increases first and then decreases, and the contact
Angle decreases first and then increases. With the increase of reaction time,
the water flux of modified membrane first increases and then decreases, and the
contact Angle first decreases and then increases.
The optimal experimental conditions were as follows: mass
ratio of OCMCS/PVA was 1:1, the amount of 5wt% glutaraldehyde and 1wt%
hydrochloric acid solution was 2.5ml and 1mL, the reaction time was 6h, and the
temperature was 50℃.The ptfe-pva /OCMCS membrane prepared has a larger water flux of
4480.89L·m-2·h-1 and a contact Angle of 57.48°.The anti-pollution test results
of PTFE microporous membrane with hydrophilic modification showed that ptfe-pva
/OCMCS membrane had good anti-bsa
adsorption ability. The results of long time washing showed that ptfe-pva
/OCMCS film had good physical stability.
