32
for the dissolution, regeneration and derivatization of cellulose. As
reported by Swatloski, Spear, Holbrey, and Rogers (2002), up to
25.0 wt% of cellulose could be dissolved in ionic liquid to form a
homogeneous solution. Li and Zhao (2007) and Li, Wang, and Zhao
(2008) reported that the combination of mineral acids and ionic
liquids efficiently hydrolyzed lignocelluosic materials under mild
conditions. In the presence of 1-butyl-3-methylimidazolium chlo-
ride (BMIMCl) and HCl, total reducing sugar yields of 66–81% were
in 12.0 wt% NaOH solution overnight to remove ink residuals and
hemicelluloses, and then treated with 3.0 wt% HCl solution at 80 ◦C
for 2 h to remove any residual lignin. Cellulose fibers obtained were
washed with deionized water and dried in an oven until constant
weight at 80 ◦C. All cellulose fiber samples were dried in an oven
at 80 ◦C for 48 h before each experiment to ensure that their water
contents were consistently below 0.5 wt%.
The depolymerization of cellulose fibers using ionics liq-
(Li et al., 2009; Tao, Song, & Chou, 2011). However, study on
controlled or selective depolymerization of cellulose fibers into
cello-oligomers of varying chain-lengths is still lacking. Benoit
et al. (2011) reported on the production of cello-oligomers with
limited its widespread applications. Macroreticulated styrene-
divinylbenzene resins functionalized with sulfonic groups have
been reported to be powerful catalysts for the selective depolymer-
ization of cellulose dissolved in ionic liquid (Rinaldi, Palkovits, &
potential applications as surfactants, thickening agents and glues
(Monsan and Paul, 1995a,b; Boissou, De Oliveira Vigier, Estrine,
Marinkovic, & Jérôme, 2014), and as rheology modifiers for food
and home care applications (Zavrel, Bross, Funke, Büchs, & Spiess,
2008).
In this paper, we have reported the selective depolymerization
of cellulose fibers derived from printed paper wastes into cello-
oligmers of different degree of polymerization or chain lengths
by using an ionic liquid, 1-allyl-3-methylimidazolium chloride
(AMIMCl), as the solvent, and Amberlyst 15DRY as the acid cata-
lyst. The effects of depolymerization parameters including reaction
temperature, concentration of acid catalyst, and reaction time on
the degree of polymerization of cello-oligomers formed and the
composition of depolymerized products were investigated.
The room temperature ionic liquid, AMIMCl, was synthe-
sized according to the method reported by Zhang, Wu, Zhang,
and He (2005) with some modifications. Typically, 100 mL of
1-methylimidazole was placed into a 500 mL three neck round
bottom flask, and then 120 mL of allyl chloride was being added
dropwise to the flask at room temperature under inert condition.
The reaction mixture was stirred magnetically under reflux at 55 ◦C
for about 8 h. The unreacted allyl chloride was removed by rotary
evaporator under reduced pressure, whereas the residual of 1-
methylimidazole was eliminated by washing thrice with an excess
amount of ether. The resulting ionic liquid was stored with molec-
ular sieve in a vacuum desiccator.
The depolyemerization of cellulose fibers was conducted by
dissolving 0.25 g cellulose fibers in 5.00 mL of AMIMCl at 80 ◦C
under mechanical stirring. Upon complete dissolution of cellulose
fibers, 0.10 mL of water was added into cellulose solution using
a micropipette. The cellulose solution was mechanical stirred for
2 min and then 0.05 g of Amberlyst 15 DRY catalyst (0.23 mmol
H3O+g−1) was added. Cello-oligomers formed after fixed reac-
tion durations were regenerated by adding water dropwise into
the reaction medium. Regenerated cello-oligomers were separated
by centrifugation at 6000 rpm, and washed with ultrapure water
until no chloride ions was detected using 0.1 M silver nitrate solu-
tion. Cello-oligomer samples were dried at 60 ◦C in an oven until
constant weight, weighed and stored in a vacuum desiccators.
The liquid fraction was collected and stored in a freezer for DNS
assay and HPLC analysis. Experimental parameters such as reac-
tion temperature (70–120 ◦C), equivalent H3O+ ions concentration
(0.115–1.84 mmol), and reaction time (10–120 min) were varied
for studying their effects on the yields and degree of polymeriza-
tion (DP) or chain length of regenerated cello-oligomers, as well as
yields of water-soluble oligosaccharides.
2. Methods
2.1. Materials
Printed paper wastes were collected from the Faculty of
Resource and Science Technology, Universiti Malaysia Sarawak.
Sodium hydroxide (NaOH), hydrochloric acid (HCl), Silver nitrate
(AgNO3), sulphuric acid (H2SO4) were purchased from Merck
(American Pharmaceutical Company) whereas 1-methylimidazole,
allyl-chloride, copper(II) ethylenediamine complex solution,
(1.0 M) and dimethyl sulfoxide (DMSO)were obtained from Sigma-
Aldrich (American Life Science and High Technology Company).
Both potassium sodium tartrate and phenol were purchased from
JT Baker (Avantor Performance Materials). All chemicals were used
without further purification.
2.4.1. Determination of viscosimetric degree of polymerization
(DPv)
The degree of polymerization of cellulose was determined by
measuring the intrinsic viscosity of cellulose in copper(II) ethylene-
diamine complex solution (CED) according to ISO 5351: 2012.
Typically, 0.50 wt% of cellulose fibers was placed in bijou bottles and
10.0 mL of water was added. The mixture was stirred at room tem-
perature for 30 min in order to swell the cellulose fibers. 10.0 mL of
CED was then added to the bottle and purged with nitrogen gas for
5 min. The sample was stirred until complete dissolution of cellu-
lose which was confirmed by examining 100 L mixture solution
efflux time of the cellulose solution using a viscometer (Canon Cal-
ibrated Ubbelohde) for at least 3 times. Mean DPv values of the
cellulose samples were calculated based on the following equation
(Marx-Figini, 1978):
2.2. Extraction of paper cellulose
Cellulose fibers were extracted from printed paper waste based
on the method reported by Wang, Li, and Zhang (2013). Typically,
printed paper wastes were grinded, dispersed by soaking in water
and stirred continuously at 2000 rpm for 2 h, and subsequently fil-
tered with a sieve. The resulting paper pulp sample was submerged
[ŋ] = 0.42 DPv
(1)