Chemical Engineering January 2022 - 26

prior to laboratory-scale process
development. Beginning with low
crosslinker addition, the impact on
the reaction was monitored for heat
of reaction and byproducts.
The commercial-scale production
of Walocel M120-01 Cellulose Ether
has been running without incident
since 2019 at a sold-out scenario of
the production assets. So, the new
process implementation required a
tight implementation batch schedule
as well as a low-risk approach to help
minimize off-specification production.
HONOR ACHIEVEMENT
DowPolyurethanes
Syntegra™ PU Dispersion
Due to its similarities with actual
leather, microfiber leather has become
the
dominant
replacement
material for genuine leather in recent
years. However, current processes
for making microfiber leather have
severe deficiencies. Syntegra Waterborne
Polyurethane (PU) Dispersions
are solvent-free dispersions
that achieve high performance with
an excellent sustainability profile.
Microfiber leather manufacturers
can use Syntegra Waterborne Polyurethane
Dispersions in their existing
processes to produce the most
sustainable, high-quality microfiber
leather available.
Presently, the most commonly used
process of microfiber leather production
is based on the polyurethane-indimethylformamide
(DMF) solution
approach. First,
the
pre-fabricated
solution,
folnonwoven
sheet is impregnated into
25-35% PU-in-DMF
lowed by washing with DMF-water
mixtures to reduce the DMF content
and microcellular structure generation.
Then the formed intermediate
sheet will be washed by toluene or
sodium hydroxide aqueous solution
to remove unnecessary fiber components
to generate the " micro " fiber
structure. Finally, the microfiber leather
will be finished by drying. In the whole
procedure, DMF is used due to its low
viscosity, easy processability and porous
structure generation.
However, DMF is classified as a
Substance of Very High Concern by
the European Chemicals Agency.
The ZDHC (Zero Discharge of Hazardous
Chemicals) has set proac26
Dow
Conventional
solvent
DMFPU
process
SYNTEGRATM
PUD ECO
process
FIGURE 4. The waterborne PU dispersion process by Dow Syntegra YF4000 PUD is much simpler than the
DMF-PU process. DMF-PU processes are easily retrofitted for Syntegra
tive goals to reduce DMF use in the
leather industry for the coming years.
Aqueous polyurethane dispersions
(PUD) are regarded as one of
the most promising eco-friendly solutions
for DMF replacement. These
realize a low viscosity and a high PU
resin content system by dispersing
the PU particles into water. However,
the synthetic leather industry is still
facing technical challenges associated
with PUD microfiber fabrication.
Generating " leather-like " haptics is
very challenging with a good chemical
resistant PUD.
In response to these technical
challenges, Dow developed
and
commercialized Syntegra YF4000
PUD for waterborne microfiber
leather
are generated
fabrication, as well as its
post-formulation and process for
good haptics microfiber leather.
These dispersions
using Dow's patented Bluewave
technology. Synthetic leather can be
designed by varying the PU polymer
structure to create a cost-effective
product
with excellent
chemical
resistance. Bluewave technology,
utilizing a process intensive continuous
dispersing device, generates
an easy-to-disperse product
without using organic solvents. The
final PUD product has a high solid
content (>54%), which saves shipping
costs (reduces the transportation
of water and packaging sizes),
conserves energy and reduces the
overall carbon footprint for the product.
Additionally, Syntegra lends itself
to be easily implemented with
a simple retrofit of existing solventbased
processes (Figure 4).
In a conventional DMF-PU process,
there is one DMF-PU tank for
resin impregnation and several DMFwater
tanks for washing and an additional
DMF-water distillation step
needed to separate DMF and water.
With Dow's waterborne process,
only a single impregnation PUD
tank is needed, followed with a drying
oven to remove the water. Since
the impregnation tank and oven are
already installed in most synthetic
leather factories, no new design or
capital investments are required to
implement Dow's new technology.
Mechanical dispersing process.
Dow's proprietary Bluewave Mechanical
Dispersing Process is the foundational
technology needed to create
the emulsified polyether-based PUD.
Bluewave technology utilizes the
high-internal-phase emulsion (HIPE)
mechanism to generate sub-micron
polyurethane particles using a surfactant
that is effective without an organic
solvent. With accurate metering
of the PU prepolymer, surfactant and
water into a novel rotor/stator in-line
mixer, a well-defined particle size distribution
can be generated. Within the
same rotor/stator, reaction of these
particles with an amine chain extender
allows tailoring of the physical
properties of the PUD. Finally, water is
injected within this novel rotor/stator
to break up and dilute the HIPE to the
desired final solids level. This compact
and efficient process generates
the PUD continuously with particle
formation, reaction and dilution steps
occurring within seconds.
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Chemical Engineering January 2022

Table of Contents for the Digital Edition of Chemical Engineering January 2022