E-beam Effect on Bacterial Cellulose Membrane and its Potential in
Filtration
Pikul Wanichapichart1,3, Wirach Taweepreeda2, Safitree Nawae1, Dan Yasenchak4
1Membrane
Science and Technology Research Center, Department of Physics, Prince of
Songkla University, Thailand
2Polymer Science Program, Prince of Songkla University, Thailand
3ThEP Center, CHE, Bangkok, Thailand
4E-Beam Services, Inc. OH 45036, USA
[email protected]
Abstract
Two types of bacterial cellulose (BC) membranes were produced under a modified H&S medium using
sucrose as a carbon source, with (CCB) and without (SHB) coconut juice supplement. It was found that
coconut juice enhanced cellulose production and hence the thickness of the formed CCB membrane was
greater than that of the SHB one. These membranes possessed similar crystallinity and were classified as
UF membrane type with mean pore size of about 0.1 m. They were hydrophilic with water contact angle of
about 30 degree. Its potential for waste water treatment was performed. After being irradiated with E-beams,
membrane water contact angle was increased to about 40 degree. This explained a reduction in water flux of
both membranes after the irradiation. However, filtration of polyethylene glycol revealed that membrane
molecular weight cut off (MWCO) of the membranes was increased. This effect was confirmed by smaller
rejection of cadmium and nickel of the treated membranes, compared to the control. SEM micrographs and
FTIR analysis revealed membrane morphology and changes in functional groups at the membrane surface,
respectively. The changes also indicated a reduction of water molecules at the surface. It was concluded that
E-beams caused polymer scissoring effect in cellulose membranes.
Keywords: Bacterial cellulose- filtration- wastewater-e-beam effect-molecular weight cut off
Introduction
Cellulose has been utilized in many applications; namely food additive, wound dressing, drug delivery, tissue
engineering and wastewater treatment, due to its biocompatibility, biodegradable and environmental friendly.
Pure cellulose was produced by A. xylinum under controlled conditions and selected medium for carbon
source. Wet mass of the produced cellulose, the thickness of the obtained membranes and the percentage
of crystalline were compared. Waste water from rubber industry and hospital discharge was filtered for its
preliminary potential. Membrane characterization was carried out in comparison between treated and
untreated membranes by irradiation of electron beams.
Methods
Water swollen property was obtained by weighing the membrane before and after being left in water for
several period of time. Hydraulic permeability was estimated from a slope of water flux against the applied
pressure in a dead-end filtration unit. Molecular weight cut off of the membrane was obtained from 90%
rejection of various polyethylene glycol (PEG) molecular weights. Surface morphology was studied using a
scanning electron microscope, while functional groups of cellulose membrane were analyzed using Fourier
Transform Infrared Spectrometer spectrometer.
RESULTS
The produced bacterial cellulose absorbed water by 80% within 30 min. in distilled water and reached 160%
within 2 hrs in SHB membrane. After being irradiated with E-beam, the water permeability coefficient has
been reduced. From ATR-FTIR study, changes in major characteristic peaks of cellulose membrane are
revealed in Figure 1. Figure 2 shows MWCO of the treated membranes compared to the un-treated ones. As
is seen, the E-beam increased the cut off of both membrane types. Filtration of nickel and cadmium was
carried out and it was found that the rejection of the former was only 5%, smaller than that of the latter
(34%), due to its smaller size. The rejection was further reduced after the E-beam irradiation. This result
agreed well with the cut off result.
Figure 1 ATR-FTIR spectra of cellulose membrane,
comparing the un-treated membranes with the treated
one under limited (A) and ambient (B) oxygen
condition.
%Transmittance
Cellulose membrane
B
A
4000
3500
3000
2500
Wave number
2000
1500
1000
/cm-1
100
CE(CCB) control
90
CE(CCB) A
80
CE(CCB) B
CE(SHB) control
70
% Reject
They are at 3340 cm−1 (O–H stretch), 2894 cm −1 (C–H
stretch), 1641 cm −1 (C=O stretch of carbonyl group),
1360 cm−1 (C–H stretch of methyl group), 1160 cm −1
(bridge O stretch), and at 1050 cm −1 (C–O stretch).
However, after E-beam irradiation cellulose molecule
might be destroyed. The peak at 713 (O-H out-of-plane
bend) and 3340 (hydroxyl group, H-bonded OH stretch)
decreased remarkably indicating changing in number of
water molecules surrounding, inducing a hydrophobic
property of the membrane. This effect leads to depolymerization, which is known to enhance the
radiation-chemical degradation. The reaction between
two chains of cellulose radicals might cause chain
cross-linking and increasing in the molecular weight of
cellulose. However, this result disagreed with the
results obtained from molecular weight cut off studies
and Cd and Ni filtration.
Figure 2 Percentage of rejection
using several PEG molecular
weights.
CE(SHB) A
60
CE(SHB) B
50
40
30
20
10
0
0
5000
10000 15000 20000 25000 30000 35000 40000
Molecular weight (Da)
Conclusion
Bacterial cellulose membranes showed potential for using as a pretreatment of wastewater. After being
irradiation with E-beam, the membrane surface structure was changed such that water permeability was
reduced. However, the pore size in term of molecular weight cut off was increased. This disagreement might
be due to the increase in water contact angle which induced the membrane hydrophobicity. The increase in
membrane MWCO and the decrease in nano-particle rejection suggested a scissoring effect of the E-beam
on this membrane type.
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