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mechanical properties and the advantage of cold drawing was
clearly demonstrated.The present paper is an attempt to orient TEMPO-NFC in
the nanopaper by cold-drawing of the wet “hydrogel cake”
resulting from filtration and containing 70−90% water. No
organic solvent is used. A three-step papermaking route is used
including vacuum filtration, hydrogel drawing and drying.
Effects of drawing on fibril orientation and on mechanical
properties of oriented nanopaper are evaluated. In the last part,
we show the applicability of the drawing method for TEMPO-
NFC based nanocomposites using hydroxyethyl cellulose
(HEC) as a matrix. Effects of the polymer matrix on the
mechanical properties of the drawn TEMPO-NFC nano-
composites are discussed. In a recent conference, independent
work on oriented nanopaper was presented orally and as an
abstract.
35
This paper additionally discusses the cold-drawing of
TEMPO-NFC based composites.Disintegration of TEMPO-NFC. TEMPO-NFC aqueous dis-
persion was prepared from softwood sulphite pulp fibers (DP of 1200,
lignin and hemicelluloses contents of 0.7% and 13.8%, respectively,
Nordic Paper Seffle AB, Sweden) according to the TEMPO-mediated
oxidation method reported by Saito et al.
8
The pulp was first dispersed
in water in which sodium bromide and TEMPO were dissolved (1 and
0.1 mmol per gram of cellulose, respectively). The concentration of
the pulp in water was 2 wt %. The reaction was started by addition of
sodium hypochlorite (10 mmol per gram of cellulose) dropwise into
the dispersion. During the addition of NaClO, carboxylate groups were
forming on the surface of the fibrils and the pH decreased. The pH of
the reaction was then maintained at 10 by sodium hydroxide addition
(i.e., the pulp fibers in the salt form). After all NaClO was consumed,
the pulp fibers were filtered and washed several times with deionized
water until the filtrate solution was neutral. The purified pulp fibers
were then dispersed in water at a concentration of 1 wt % and
disintegrated by a homogenization process with a Microfluidizer M-
110EH (Microfluidics Ind., USA). The carboxylate content of
TEMPO-NFC determined by titration is 2.3 mmol g−1
.
Preparation of Reference TEMPO-NFC Nanopaper. Prepara-
tion of NFC Nanopaper was reported previously.
5
The 1 wt %
TEMPO-NFC dispersion was diluted to 0.1% by water addition and
stirring and subsequently degassed. The 0.1% TEMPO-NFC
dispersion was vacuum filtered on a glass filter funnel (7.2 cm in
diameter) using filter membrane, 0.65 μm DVPP, Millipore. After
filtration, a wet “cake” is formed. The cake has a water content of 70−
90% as determined on a series of cakes obtained after vacuum filtration
using oven drying at 105 °C. This cake is peeled from the membrane
and stacked first between two woven metal cloths and then two paper
carrier boards. This package was placed in a sheet dryer (Rapid
Kothen-Rycobelgroup) for 12 min at 93 °C and a vacuum of about 70
mbar. The resulting nanopaper had a thickness of ca. 50 μm.
Cold Drawn TEMPO-NFC Nanopaper with Partial Alignment
of the Fibrils. The wet TEMPO-NFC cake is prepared as above.
From the cake, 1 cm wide strips were cut, clamped on a tensile testing
equipment (Instron 5944) and stretched at a tensile rate of 50% min−1
until the strain reached 20, 40, or 60% (corresponding to draw-ratio
DR of 1.2, 1.4, and 1.6 respectively). The stretching was stopped, and
the samples were taken in the stretched conformation, tapped into
woven metal cloths and put between two paper carrier boards and
dried as above.
Cold Drawn TEMPO-NFC/HEC Nanocomposite with Partial