Antimicrobial and Antioxidant Surface Modification of Cellulose Fibers
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7/17/2019 Antimicrobial and Antioxidant Surface Modification of Cellulose Fibers
Antimicrobial and antioxidant surface modification of cellulose fibersusing layer-by-layer deposition of chitosan and lignosulfonates
Hui Li a,b,c,∗, Lincai Peng b,d
a Food SafetyResearch Institute, Kunming University of Science andTechnology, Kunming 650500, Chinab State Key Laboratory of Pulp andPaper Engineering, South China University of Technology, Guangzhou510640, Chinac Key Laboratory of Pulp andPaper Science & Technology ofMinistry of Education of China, Qilu University of Technology, Jinan 250353, Chinad Faculty of Chemical Engineering, Kunming University of Science andTechnology, Kunming 650500, China
a r t i c l e i n f o
Article history:
Received 26 June 2014
Received in revised form 18 January 2015
Accepted 26 January 2015
Available online 12 February 2015
Keywords:
Layer-by-layer
Chitosan
Lignosulfonates
Antimicrobial activity
Antioxidant activity
Cellulose fibers
a b s t r a c t
To confer cellulose fibers antimicrobial and antioxidant activities, chitosan (CS)/lignosulfonates (LS) mul-
tilayers were constructed on fibers surfaces through layer-by-layer deposition technique. The formation
of CS/LS multilayers on cellulose fibers surfaces was verified by X-ray photoelectron spectroscopy (XPS)
and zeta potential measurement. The surface morphologies of CS/LS multilayers on fibers surfaces were
observed by atomic force microscopy (AFM). The results showed that characteristic element (i.e. N and
S element) content increased with increasing bilayers number, the surface LS content increased linearly
as a function of bilayers. Zeta potential of modified fibers was inversed after deposition of each layer.
AFM phase images indicated that the cellulose microfibrils on fibers surfaces were gradually covered
by granular LS aggregate. The antimicrobial testing results demonstrated that CS/LS multilayers modi-
fied fibers with CS in the outermost layer exhibited higher antimicrobial activity against Escherichia coli.
The antioxidant testing results showed that antioxidant activity of CS/LS multilayers modified fibers was
better than that of original fibers under the same oxidation conditions.
H. Li, L. Peng / Carbohydrate Polymers 124 (2015) 35–42 37
Fig. 1. XPS spectra of original and modified cellulose fibers: (a) original cellulose fibers, (b)–(d) (CS/LS)1, (CS/LS)3 and (CS/LS)5 multilayers modified cellulose fibers,
respectively.
to form 3% consistency fiber suspension, the pH of fiber
suspension was adjusted to 4 by using HCl and NaOH. Each
sample was tested in triplicate and the average value was reported
in this work.
2.3.3. Atomic force microscopy (AFM) analysis
The fibers for AFM analysis were taken from the same pulp
sheets for XPS analysis, and the sample preparation method was
as described by Liu, Fu, Zhu, Li, and Zhan (2009). A commercial
Multimode Nanoscope IIIa AFM system (Veeco, Santa Barbara, CA,
US) was used to observe the surfaces characteristics of modified
cellulose fibers. The AFM system was equipped with a J-type scan-
ner and a standard silicon cantilever with a resonance frequency
of 290–320 kHz. The scan was operated in a tapping mode in air atroom temperature with a relative humidity of 65%. Several scans
were performed from different parts of the samples and represen-
tative images were chosen for presentation. The scanning size was
1.5×1.5m. Software Version 5.12r3 (Veeco Co., USA) was used
for online data recording and software WSxM (Nnaotec Electron-
ica, Spain) was used for offline data analysis. No image processing
except flattening was made.
2.4. Antimicrobial activity of CS/LS multilayers modified cellulose
fibers
The method used for testing the antimicrobial activity of mod-
ified cellulose fibers was as described by Qian et al. (2009).
Gram-negative Escherichia coli was selected as representativemicroorganism. The procedure is as follows: The pulp sheet (0.1 g)
cut from XPS analysis sheet sample sterilized by autoclaving and
5 mL E. coli suspension (ca. 106 CFU/mL) were mixed and shaken
at 200 rpm at 37◦C for 1 h. After shaking, a series of dilutions were
made and then 100L of dilution was spread on Luria–Bertani agar
in a Petri dish. The plates were incubated at 37◦C for 24h and the
number of colonies wascounted. At least three repeated tests were
carried out for each sample. The growth inhibition degree of E. coli
can be quantified by the following equation:
Degree of growth inhibition for E. coli = A− B
A × 100% (1)
where A and B are the number of colonies of the control and tested
samples, respectively.
2.5. Antioxidant activity of CS/LS multilayers modified cellulose
fibers
2.5.1. ABAP-initiated oxidation treatment
The oxidation treatment was carried out in a reactor kettle
equipped with an automatic temperature control system, pressure
control and mechanical stirring. ABAP-initiated oxidation treat-
ment conditions were as follows: 10% ABAP (relative oven-dried
fibers), O2 pressure 140kPa, temperature 60◦C, reaction time (0, 2,
H. Li, L. Peng / Carbohydrate Polymers 124 (2015) 35–42 39
Table 1
XPSresults from cellulose fibers modified by CS/LS multilayers.
Numberof
bilayers
C 1s total= 100% ϕLS (%)
C1 (%) C2, C5 (%) C3 (%) C4 (%)
0 3.7 80.3 15.1 0.9 0
1 10.3 68.2 19.4 2.1 14.1
2 18.1 61.5 18.0 2.4 30.6
3 24.2 62.6 10.7 2.5 43.6
4 29.5 65.4 3.4 1.7 54.9
5 31.7 65.7 1.5 1.1 59.6
Fig. 5. Surface morphologies of original and modified cellulose fibers: (a) original fiber, (b)–(d) (CS/LS)1, (CS/LS)3 and (CS/LS)5 multilayers modified fibers, respectively, (e)
CS alone-modified fibers.
were regarded as LS granules aggregate. This is attributed to three
reasons: (i) the morphological character of fiber surface modified
with CS alone was very similar to that of original fiber surface and
the CS cannot be distinguished from the fiber surface as presented
in Fig. 5e; (ii) LS granules tend to aggregate in acid solution due
to hydrogen-bonding interactions (Nyman, Rose, & Ralston, 1986);
(iii) the amount of granular substances increased with the increase
in the bilayers number, which is correspondingto increasedsurfaceLS content.
3.3. Assessment of antimicrobial activity of cellulose fibers
modified by CS/LS multilayers
The degree of growth inhibition for E. coli was examined in
CS/LS multilayers modified fibers with different surface compo-
sitions and deposited bilayers. It was found from Fig. 6 that
all the modified cellulose fibers had E. coli inhibition activity
because of the presence of CS. The growth inhibition degree
of (CS/LS)4.5 multilayer modified cellulose fibers reached to
97%, while the growth inhibition degree of (CS/LS)5 multi-
layer modified cellulose fibers was less than 63%, indicating
that the antimicrobial activity of the samples with CS in the
outermost layer was better than that of the samples with
LS in the outermost layer. Furthermore, the growth inhibition
degree increased with the increasing bilayers number when the
CS in the outermost layer. These results may be caused by
three reasons: (1) CS has antimicrobial activity; (2) the E. coli
absorption and immobilization capacities of CS were increased
because of its hydrophilicity and higher positive charge; (3) the
increase in surface RMS roughness of modified cellulose fibers led
to higherspecific area, whichmay causeefficientcontactand inter-action between CS andE. coli.
3.4. Assessment of antioxidant activity of cellulose fibers modified
by CS/LS multilayers
Degree of polymerization reflects the average length of cellulose
chains. The zero-span tensile strength is a widely used index for
evaluating the average strength of individual fiber. Fig. 7 shows
plots of DP and zero-span tensile strength of original and modified
cellulose fibers against oxidation reaction times. It is clearly seen
that DP and zero-span tensile strength of original cellulose fibers
dramatically decreased as the oxidation reaction time increased,
whichis dueto attackof radical to cellulosechains,thereby causing
depolymerization and strength loss of cellulosefibers. For the CS/LSmultilayers modified cellulose fibers, the DP and zero-span tensile
strength gently decreased with increasing oxidation reaction time.
As the number of bilayers increased, the changes in the DP and
zero-span tensile strength of modified fibers became level off. This
can be explained that LS layers on modified fibers surfaces acted
as natural radical scavenger, which protected cellulose fiber from
radicals attacking.
In this study, a probable radical oxidation mechanism is shown
in Scheme 2. Radical initiator ABAP is a water-soluble azo, which
can rapidly decomposed at 60◦C, producing two carbon-centerd
radicals (R •). R • reacted with oxygen to generate peroxyl radical
(ROO•), which attracted the cellulose, resulting in cellulose chain
fragmentation and generating cellulose radical (Cell•). The Cell•
reacted with oxygen to produce Cell-OO•
and attracted cellulose.
The presence of ROO• and Cell-OO• will cause both depolymeriza-
tionand propagationof theradicalchain.LS are a phenolicpolymers
which inhibit ABAP-initiated oxidation reactions by trapping the
chain-propagating ROO•. The LS phenolic polymers gives up their
phenolic hydrogen atom to ROO•, producing phenoxyl radical
PhO•, terminating chain reaction between ROO• and cellulose.
Simultaneously, colored non-radical products such as quinones
were formed by PhO• coupling reaction.
4. Conclusions
The antimicrobial and antioxidant surfaces modification of cel-
lulose fibers were achieved through constructing CS/LS multilayers
on fibers surfaces via layer-by-layer deposition technique. The
increase in characteristic elements (N and S) of CS/LS multilay-
ers with the number of bilayers was observed, and the surface LS
content of modified cellulose fiber linearly increased as a function
of bilayers. The surface zeta potential of modified cellulose fibers
was inversed after each deposition step. The AFM phase images
showed that the granular LS aggregate gradually covered the cel-
lulose fibers surfaces as the LBL deposition proceeded, resulting in
the increase in fibers surfaces roughness. The antimicrobial testingresults demonstrated that cellulose fibers modified by CS/LS mul-
tilayers exhibited higher antimicrobial activity against E. coli, the
degree of E. coli growth inhibition for a (CS/LS)4.5 multilayer modi-
fied cellulose fibers reached up to 97%. TheE. coligrowth inhibition
degree increased with the increasing bilayers number, especially
E. coli growth inhibition degree of modified cellulose fibers with
CS in the outmost layer was better than that of the cellulose fibers
withLS in theoutmostlayer. Theantioxidanttestingresultsshowed
that there was almost no change in the DP and zero-span tensile
strength of modified fibers after ABAP-initiated oxidations due to
the presence of radical scavenger LS. Moreover, the antioxidant
activity of CS/LS multilayers modified cellulose fibers increased
with the bilayers number increased.
Acknowledgements
This work wassupportedby theApplied BasicResearchProgram
of Yunnan Province (no. 2014FD008), Talent Training Program of
Yunnan Province (no.KKSY201305002), State Key Laboratory Open
Foundation of Pulp and Paper Engineering of China (no. 201323)
and Open Foundation of Key Lab of Pulp and Paper Science &Tech-
nology of Ministry of Education (no. 08031349).
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