Tech Briefs Magazine - August 2021 - 42

Sustainable Technology
results show that xylem filters have
potential for use in community settings
to remove bacteria and viruses from contaminated
drinking water.
The researchers are exploring options
to make xylem filters available at large
scale, particularly in areas where contaminated
drinking water is a major cause of
disease and death. The team launched an
open-source website with guidelines for
designing and fabricating xylem filters
from various tree types.
The woody material's natural filtering
ability had some natural limitations. As
the wood dried, the branches' sieve-like
membranes began to stick to the walls,
reducing the filter's permeance, or ability
to allow water to flow through. The filters
also appeared to " self-block " over
time, building up woody matter that
clogged the conduits.
Two simple treatments overcame both
limitations. By soaking small cross-sections
of sapwood in hot water for an
hour, then dipping them in ethanol and
letting them dry, the material retained
its permeance, efficiently filtering water
without clogging up. Its filtering could
also be improved by tailoring a filter's
thickness according to its tree type.
The researchers tested the filters' ability
to remove contaminants such as E.
coli and rotavirus - the most common
cause of diarrheal disease. The treated
filters removed more than 99 percent of
both contaminants.
Xylem tissue in gymnosperm sapwood can be used for water filtration (as seen on top). Xylem is
comprised of conduits that are interconnected by membranes that filter out contaminants present
in water (bottom). (Credit: N.R. Fuller, Sayo Studio)
Solvent-Based Recycling Process
By reclaiming polymers in plastics, the process could cut down on millions of tons of
plastic waste.
University of Wisconsin, Madison
ultilayer plastic materials are ubiquitous
in food and medical supply
packaging, particularly since the specific
properties of layered polymers can keep
moisture from fouling sterile syringes, or
light and oxygen from making potato
chips stale. But despite their utility, those
ever-present plastics are impossible to recycle
using conventional methods.
About 100 million tons of multilayer
thermoplastics - each composed of as
many as 12 layers of varying polymers -
are produced globally every year. Forty
percent of that total is waste from the manufacturing
process itself and be cause there
has been no way to separate the polymers,
almost all of that plastic ends up in landfills
or incinerators.
M
A team of engineers has pioneered a
method for reclaiming the polymers in
these materials using solvents - a technique
called Solvent-Targeted Recovery
and Precipitation (STRAP) processing. By
42
Cov
using a series of solvent washes guided by
thermodynamic calculations of polymer
solubility, the team used the STRAP pro -
cess to separate the polymers in a commercial
plastic composed of common layering
materials polyethylene, ethylene
vinyl alcohol, and polyethylene terephthalate.
The separated polymers appear chem -
ically similar to those used to make the
original film.
The team now hopes to use the recovered
polymers to create new plastic materials,
demonstrating that the pro cess can
help close the recycling loop. In particular,
it could allow multilayer-plastic manufacturers
to recover the 40 percent of plastic
waste produced during the production
and packaging processes. The process was
demonstrated with one multilayer plastic;
the team will try other multilayer plastics
and scale the technology.
As the complexity of the multilayer plastics
increases, so does the difficulty of idenwww.techbriefs.com
ToC
tifying
solvents that can dissolve each polymer.
That's why STRAP relies on a computational
approach called the Conductorlike
Screening Model for Realistic Solvents
(COSMO-RS) to guide the process.
COSMO-RS is able to calculate the solubility
of target polymers in solvent mixtures
at varying temperatures, narrowing
down the number of potential solvents
that could dissolve a polymer. The team
can then experimentally explore the candidate
solvents. The goal is to eventually
develop a computational system that will
allow researchers to find solvent combinations
to recycle all sorts of multilayer plastics.
The team also hopes to look at the
environmental impact of the solvents it
uses and establish a database of green solvents
that will allow them to better balance
the efficacy, cost and environmental im -
pact of various solvent systems.
For more information, contact Kelly Tyrrell
at kelly.tyrrell@wisc.edu; 608-262-9772.
Tech Briefs, August 2021
A prototype of a simple filtration system
was fitted with a receptacle at the top
that users can fill with water. The water
flows down a 1-meter-long tube, through
a xylem filter, and out through a valvecontrolled
spout. The xylem filter can be
swapped out either daily or weekly, de -
pending on a household's needs.
For more information, contact Abby
Aba zorius at abbya@mit.edu; 617-253-2709.

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Tech Briefs Magazine - August 2021

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