Abstract
Use of foam instead of water as a material carrier in the
manufacturing of novel paper-like structures has recently
been studied intensively [1]. The technology can provide
materials with striking new features such as tailored
microporous structures. Here the control of the foam
properties including air content, bubble size, rheology
and stability becomes important. To address these
problems, we have investigated aqueous foams and their
interaction with cellulose fibers both in axial mixing
[2] and in pipe flow [3].
In axial mixing, the bubble size is affected by several
factors such as rotational speed, air content and surface
tension. The link between bubble size and air content can
be described by a simple formula based on considering the
effect of total interface area on the surface excess
concentration of surfactant. At high shear rates, the
bubble size becomes small and the importance of surface
interactions increases affecting the rheological
behaviour described by the Herschel-Bulkley equation.
Response of wet foam to inclusion of natural and
regenerated cellulose fibers is quite different with
smaller mean bubble size for natural fibres than for
regenerated fibres. The likely reason behind this
behaviour is the rough surfaces of the natural fibers and
their fine particle fraction.
In pipe flow, the strongest impact on viscosity was
created by hardwood fibers with rich surface texture and
their mean length exceeding the average bubble diameter
by an order of magnitude. The observed effect on
viscosity was still much smaller than in the case of
plain aqueous fiber suspension. Fibers do not interact or
flocculate in foams to the same extent as in water
suspensions. Thus, the fiber networks produced using foam
forming are generally very homogeneous.
1) A. M. Al-Qararah, A. Ekman, T. Hjelt, J. A. Ketoja, H.
Kiiskinen, A. Koponen, J. Timonen, A unique
microstructure of the fiber networks deposited from
foam-fiber suspensions. Colloids and Surfaces A:
Physicochem. Eng. Aspects 482, 544-553 (2015).
2) A. M. Al-Qararah, T. Hjelt, A. Koponen, A. Harlin, J.
A. Ketoja, Response of wet foam to fibre mixing. Colloids
and Surfaces A: Physicochem. Eng. Aspects 467, 97-106
(2015).
3) A. Jäsberg, P. Selenius, A. Koponen, Experimental
results on the flow rheology of fiber-laden aqueous
foams. Colloids and Surfaces A: Physicochem. Eng. Aspects
473, 147-155 (2015).
Original language | English |
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Pages | CELL 295 |
Publication status | Published - 2016 |
MoE publication type | Not Eligible |
Event | 251st ACS National meeting and Exposition - San Diego, United States Duration: 13 Mar 2016 → 17 Mar 2016 |
Conference
Conference | 251st ACS National meeting and Exposition |
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Country/Territory | United States |
City | San Diego |
Period | 13/03/16 → 17/03/16 |
Keywords
- foam
- cellulose
- fiber
- technology
- bubble
- structure
- rheology