The world of plastics, in numbers

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Millions of tons of plastic are manufactured every year.
Bert Kaufmann/Wikimedia, CC BY

Eric Beckman, University of Pittsburgh

From its early beginnings during and after World War II, the commercial industry for polymers – long chain synthetic molecules of which “plastics” are a common misnomer – has grown rapidly. In 2015, over 320 million tons of polymers, excluding fibers, were manufactured across the globe.

Until the last five years, polymer product designers have typically not considered what will happen after the end of their product’s initial lifetime. This is beginning to change, and this issue will require increasing focus in the years ahead.

The plastics industry

“Plastic” has become a somewhat misguided way to describe polymers. Typically derived from petroleum or natural gas, these are long chain molecules with hundreds to thousands of links in each chain. Long chains convey important physical properties, such as strength and toughness, that short molecules simply cannot match.

“Plastic” is actually a shortened form of “thermoplastic,” a term that describes polymeric materials that can be shaped and reshaped using heat.

The modern polymer industry was effectively created by Wallace Carothers at DuPont in the 1930s. His painstaking work on polyamides led to the commercialization of nylon, as a wartime shortage of silk forced women to look elsewhere for stockings.

When other materials became scarce during World War II, researchers looked to synthetic polymers to fill the gaps. For example, the supply of natural rubber for vehicle tires was cut off by the Japanese conquest of Southeast Asia, leading to a synthetic polymer equivalent.

Curiosity-driven breakthroughs in chemistry led to further development of synthetic polymers, including the now widely used polypropylene and high-density polyethylene. Some polymers, such as Teflon, were stumbled upon by accident.

Eventually, the combination of need, scientific advances and serendipity led to the full suite of polymers that you can now readily recognize as “plastics.” These polymers were rapidly commercialized, thanks to a desire to reduce products’ weight and to provide inexpensive alternatives to natural materials like cellulose or cotton.

Types of plastic

The production of synthetic polymers globally is dominated by the polyolefins – polyethylene and polypropylene.

Polyethylene comes in two types: “high density” and “low density.” On the molecular scale, high-density polyethylene looks like a comb with regularly spaced, short teeth. The low-density version, on the other hand, looks like a comb with irregularly spaced teeth of random length – somewhat like a river and its tributaries if seen from high above. Although they’re both polyethylene, the differences in shape make these materials behave differently when molded into films or other products.

Polyolefins are dominant for a few reasons. First, they can be produced using relatively inexpensive natural gas. Second, they’re the lightest synthetic polymers produced at large scale; their density is so low that they float. Third, polyolefins resist damage by water, air, grease, cleaning solvents – all things that these polymers could encounter when in use. Finally, they’re easy to shape into products, while robust enough that packaging made from them won’t deform in a delivery truck sitting in the sun all day.

However, these materials have serious downsides. They degrade painfully slowly, meaning that polyolefins will survive in the environment for decades to centuries. Meanwhile, wave and wind action mechanically abrades them, creating microparticles that can be ingested by fish and animals, making their way up the food chain toward us.

Recycling polyolefins is not as straightforward as one would like owing to collection and cleaning issues. Oxygen and heat cause chain damage during reprocessing, while food and other materials contaminate the polyolefin. Continuing advances in chemistry have created new grades of polyolefins with enhanced strength and durability, but these cannot always mix with other grades during recycling. What’s more, polyolefins are often combined with other materials in multi-layer packaging; while these multi-layer constructs work well, they are impossible to recycle.

Polymers are sometimes criticized for being produced from increasingly scarce petroleum and natural gas. However, the fraction of either natural gas or petroleum used to produce polymers is very low; less than 5 percent of either oil or natural gas produced each year is employed to generate plastics. Further, ethylene can be produced from sugarcane ethanol, as is done commercially by Braskem in Brazil.

How plastic is used

Depending upon the region, packaging consumes 35 to 45 percent of the synthetic polymer produced in total, where the polyolefins dominate. Polyethylene terephthalate, a polyester, dominates the market for beverage bottles and textile fibers.

Building and construction consumes another 20 percent of the total polymers produced, where PVC pipe and its chemical cousins dominate. PVC pipes are lightweight, can be glued rather than soldered or welded, and greatly resist the damaging effects of chlorine in water. Unfortunately, the chlorine atoms that confer PVC this advantage make it very difficult to recycle – most is discarded at the end of life.

Polyurethanes, an entire family of related polymers, are widely used in foam insulation for homes and appliances, as well as in architectural coatings.

The automotive sector uses increasing amounts of thermoplastics, primarily to reduce weight and hence achieve greater fuel efficiency standards. The European Union estimates that 16 percent of the weight of an average automobile is plastic components, most notably for interior parts and components.

Over 70 million tons of thermoplastics per year are used in textiles, mostly clothing and carpeting. More than 90 percent of synthetic fibers, largely polyethylene terephthalate, are produced in Asia. The growth in synthetic fiber use in clothing has come at the expense of natural fibers like cotton and wool, which require significant amounts of farmland to be produced. The synthetic fiber industry has seen dramatic growth for clothing and carpeting, thanks to interest in special properties like stretch, moisture-wicking and breathability.

The ConversationAs in the case of packaging, textiles are not commonly recycled. The average U.S. citizen generates over 90 pounds of textile waste each year. According to Greenpeace, the average person in 2016 bought 60 percent more items of clothing every year than the average person did 15 years earlier, and keeps the clothes for a shorter period of time.

Eric Beckman, Professor of Chem/Petroleum Engineering, University of Pittsburgh

This article was originally published on The Conversation. Read the original article.


Why we’re watching the giant Australian cuttlefish

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Hello little ones! Juvenile giant Australian cuttlefish developing under rocks in the waters of South Australia.
Fred Bavendam, Author provided

Bronwyn GIllanders, University of Adelaide

Australia is home to the world’s only known site where cuttlefish gather to mate en masse.

From May to August, if you head into the water around Point Lowly, South Australia, it will be a chilly 12℃. But you’ll be able to observe what look like aliens – hundreds, even thousands of tentacled organisms with their unusual distinctive W-shaped eye pupils, and pulsating colours moving across their body.

Intent on mating, the cuttlefish will be totally oblivious to your presence.

Giant Australian cuttlefish can change the colour and texture of their skin.
David Wiltshire, Author provided

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But this population of cuttlefish dropped in abundance from an estimated 150,000 animals in the late 1990s to only 13,492 in 2013.

Although counts in recent years suggest the creatures have recovered, my research aims to determine what sorts of factors influence this very unique cuttlefish population. This may allow us to better manage and protect the species – important not just for science, but also for the local environment and economy.

Rockstars of the sea

Every time I head to the Point Lowly coastline and dive with the giant Australian cuttlefish I’m amazed and excited by their antics.

Giant Australian cuttlefish in an intimate embrace.
Matt McMillan, Author provided

The name “giant” is perhaps a misnomer. Giant Australian cuttlefish only ever reach about one metre in size. Most animals are much smaller, especially in South Australia.

Cephalopods have been described as rockstars of the sea for their “live fast, die young” life history strategy – they grow rapidly, reproduce early and die following reproduction. Giant Australian cuttlefish live for 1-2 years.

Although they are found in waters across southern Australia, giant Australian cuttlefish live in distinct populations that do not interact. We know from genetic studies that those breeding along that small area of Upper Spencer Gulf coastline are restricted to an area north from a line across the gulf from Wallaroo to Arno Bay (around 6,500 km²).

The most northern waters of Upper Spencer Gulf in South Australia host a unique population of giant Australian cuttlefish.
Ellen Rochelmeyer (using Google Maps), CC BY-NC-ND

Outside the breeding season of May to August they are distributed throughout this northern region. Come May they start to move towards a narrow 8km stretch of rocky coastline. At their peak you see literally one cuttlefish per square metre. It’s the sheer numbers that are impressive!

They come solely for one purpose over winter – to find mates to reproduce.

Cuttlefish gather to breed from May-August each year.
Tim Rogers, Author provided

Sudden drop in numbers

Around the late 1990s, the cuttlefish breeding aggregation in the Upper Spencer Gulf began to be targeted by fishers. Since then, a number of restrictions on taking cuttlefish and other cephalopods from these waters have been in place.

Around that time, a program of research through the University of Adelaide and SARDI Aquatic Sciences also began. Estimates of abundance and biomass of the breeding aggregation population suggested around 150,000 cuttlefish bred in the Upper Spencer Gulf. The surveys stopped after a few years.

Numbers of giant Australian cuttlefish in the Upper Spencer Gulf fell dramatically between the late 1990s and 2013.
Matt McMillan, Author provided

Then in 2005 anecdotal reports from SCUBA divers suggested cuttlefish were less abundant. A survey at that time and continual data collected since 2008 confirmed that numbers had dropped. In 2013 less than 15,000 individuals were estimated on the breeding aggregation.

Significant resources were put towards studying the cuttlefish to determine what might be causing such a decline. Changes in water temperature and salinity may be involved.

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We looked at data for other cephalopods over a similar time frame, and found no such decline. In fact, over the last 60 years many different types of cephalopod have been increasing in abundance – it’s not yet clear why.

The low numbers of 2013 seem to be unique to the giant Australian cuttlefish on the Upper Spencer Gulf.

Since this time there has been a recovery in this population, with numbers bouncing back towards their late 1990s levels.

Some giant Australian cuttlefish reach one metre in length – but most are smaller.
Nick Payne, Author provided

How cuttlefish breed

We know that cuttlefish come to this breeding aggregation to mate using a range of amazing strategies and behaviours – for example, small males impersonate females to avoid detection by larger males and gain access “under cover”.

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Because the population on the breeding aggregation is skewed towards males (an average o four to one), females have some choice over who they mate with.

After mating takes place, females deposit eggs on the underside of rocks.

Cuttlefish eggs deposited on the underside of rocks.
Fred Bavendam, Author provided

Cuttlefish eggs take three to five months to develop, hatching from mid-September through to early November. They emerge as miniature adults about the size of your thumbnail.

Baby cuttlefish disperse within the Upper Spencer Gulf with an even sex ratio.

Cuttlefish gather in only a few metres of water in the Upper Spencer Gulf.
Matt McMillan, Author provided

To work out why there was a difference in sex ratio between the broader region (1 male:1 female) and the breeding aggregation (4 males:1 female), we tagged male and female cuttlefish using trackable acoustic markers. We discovered that males spend around four times the length of time on the breeding aggregation compared to females, and that individuals are not present for the whole breeding season.

So the breeding aggregation is likely larger in size than fixed time frame counting estimates allow us to measure.

Positive influence on local economy

Although the apparently low population size in 2013 caused great concern, we are now cautiously optimistic for our giant Australian cuttlefish in Upper Spencer Gulf.

There’s something behind you!
Matt McMillan, Author provided

These creatures attract tourists from around the world, who come and snorkel or SCUBA dive on a unique breeding aggregation. This in turn injects money into the local economy and diversifies business in the region.

The cuttlefish are just one “user” of our shared marine environment along with the other activities and industries of South Australia.

The ConversationThis article is based on a presentation delivered by Bronwyn Gillanders at the South Australian Museum as part of the Sprigg Lecture Series.

Bronwyn GIllanders, Professor , University of Adelaide

This article was originally published on The Conversation. Read the original article.