Page 49 - Green Builder Magazine Nov-Dec 2017 Issue

They will work, but “there can be adverse effects on processing,
Heat Deflection Temperature Under Load mechanical properties or chemical resistance.” In other words, the
material becomes less workable.

THE ECO-ARGUMENT FOR PLASTIC LUMBER
The total recycling rate of HDPE, LDPE and PET in the U.S. was 8
percent in 1996, and has now increased to only about 10 percent for
HDPE, 5.3 percent for LPDE and 19.5 percent for PET (data from
2015 http://bit.ly/2zk3WoF).
But as WorldWatch Institute points out, plastic manufacturing has
grown at a vastly faster rate. Recycling can’t keep up with the avalanche of
waste: “From 1950 to 2012, plastics growth averaged 8.7 percent per year,
SOURCE: HTTPS://WWW.HARDIEPOLYMERS.COM/KNOWLEDGE/DESIGNING-WITH-PLASTICS/
booming from 1.7 million tons to the nearly 300 million tons of today.”
This is just one of many reasons for introducing recycled plastic-
based products into construction. Others include:
Less treated wood. Plastic lumber can replace treated wood,
which is still considered a hazardous waste material by most landfills.
Although modern treated wood has far less (if any) chromium or
arsenic, it is still infused with copper, making it hard to reuse.
Alternative to tropical and redwoods. Plastic wood has many
of the desirable durability qualities of pricey (and sometimes
endangered) South American and Asian wood species such as teak
and ipe. It can take some of the pressure off of endangered forests,
although other threats such as palm oil production have replaced
lumber sales as the biggest source of deforestation.
Flood resistance. With its natural resistance to rot and mold
growth, some plastic lumber is ideally suited for use in wet or high
flood risk locations.
Temperature matters. Additives can improve some of the issues around Garden friendly. Although more research is needed, some early
plastic softening in heat, but good system design is paramount. studies of plastic lumber in marine environments (http://bit.
deflection point of all common plastics. ly/2ixvDAu) found very little leaching, compared with treated wood
Of course, building standards, such as reducing the joist distance, alternatives. This makes it a good candidate for garden hardscapes
can compensate for some polymer weaknesses. But designers and beds.
who use RPL also face a new, emerging variable—extreme heat. Lower GHG than concrete or metals. On a pound-for-pound basis,
Progressive temperature rise and temperature spikes are expected plastic is less resource intensive than creating Portland cement or
to increase in coming years, due to climate change. melting down metals. Recycled material has far more of an edge than
Most thermoplastics do not fully melt until they reach about 250°F virgin production. And, of course, plastic has durability on its side.
(HDPE melts at between 248°F and 356°F), but they become soft and It should last for decades, before being recycled again.
bendable long before that benchmark.
Deck tests in Boston found that decks typically get up to 76°F hotter INDUSTRY LEADERS AND LAGGERS
than the ambient air (in full sun). Of course, outdoor temperatures A few building product manufacturers have recognized the ethical
would need to approach 174°F before the plastics would completely importance of recycled plastic content—and its potential to improve
melt, but in the American West, ambient temperatures frequently their bottom line. Interface (www.interface.com), for example, has
exceed 100°F. Sun-exposed HDPE products without additives could recycled about 309 million pounds of plastics over the past 20 years.
easily exceed their design limit (100°F + 76°F = 176°F). American The late CEO of Interface, Ray Anderson, set a goal of freeing the
Plastics, for example, lists 170°F as the maximum temperature company completely from use of virgin materials, and the company
acceptable for its recycled HDPE sheet polymer. seems to have remained committed to that idea. Its carpet backing
Another concern with plastics, of course, is fire. Polymers are material, Glasbac, contains about 98 percent recycled material. But
not especially ignition prone, but they burn hot and fast, igniting in the long view, Interface and others have barely scratched the
at about 540°F. As high-carbon materials, however, plastics tend problem. The carpet industry still dumps about 4.5 billion pounds
to give off a very dense black smoke. The level of toxicity varies of end-of-life product into landfills every year.
by material, but at the very least it’s disorienting and difficult for I’d also be remiss not to give a caveat to Trex (www.trex.com). Back
firefighters to navigate. in the 1980s, this company arguably launched a whole industry of
As engineer Geoffrey Pritchard notes in Reinforced Plastics composite decking where none existed. It has proven that profit and
Durability, adding fire retardants to plastics has pros and cons. recycling can be close bedfellows. And it has shown how to be more

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