Green Plastics

An Introduction to the New Science of Biodegradable Plastics

E. S. Stevens

• Publisher: Princeton University Press
• Year: 2020
• ISBN:
  9780691214177
• Topic: Sciences physiques
• Subtopic: Chimie

Plastics are everywhere. Bags, bank cards, bottles, and even boats can all be made of this celebrated but much-maligned material. Yet most of us know next to nothing about plastics. We do know that they are practical and cheap--but they also represent a huge environmental problem, for they literally take ages to decompose. In this engaging book, E.S. Stevens tells us everything we have always wondered about plastics and of the efforts, in America, Europe, and Asia, to develop a new breed of environmentally friendly plastics. He points to a possible future where plastics will no longer be made of petroleum, but of plants.
The first two chapters assess the increased use of plastics as a relatively new alternative to other materials. The third chapter introduces us to their impact on the environment and strategies for their disposal or recycling. The next two chapters cover basic concepts and terms used in polymer sciences and provide some basic chemistry. With these fundamentals in tow, the author compares how petroleum-based and biological polymers are made, and the various ways in which they decompose. He acquaints readers with the emerging technologies, their commercial viability, and their future. Finally, instructions are given for preparing basic bioplastics using readily available materials.
Nonspecialists will find Green Plastics a concise introduction to this exciting interdisciplinary topic--an introduction otherwise not available. For students it provides easy entry to an area of science with wide appeal and current importance; for teachers, excellent background reading for courses in various sciences. The prospect of depleted fossil fuel supplies, and the potential benefits of bioplastics to the environment and to rural areas that could supply the raw materials, make this book a compelling presentation of a subject whose time has come.

PART ONE

PLASTICS

1

The Age of Plastics

The New Kids on the Block

No material on earth has been so highly valued for its usefulness, yet so maligned, as plastic. We have ambivalent, contrary, and vacillating feelings about plastics, and have never finally decided whether plastics are the good, the bad, or the ugly. One reason for the ambivalence is probably their newness. The rapid growth of plastics production was a twentieth-century phenomenon, and anything less than a hundred years old, on a historical scale, is novel. Among materials, plastics are newcomers, and we simply have not had time to make up our minds about them.

Plastics are so clearly useful that it is foolish not to afford them major respect. They are often not only less expensive than alternative materials, but their properties often make them better. Their low cost has undoubtedly had life-saving consequences, as in drought-prone areas of Africa where lightweight plastic water pails, at times the most important family possession, have replaced clay and stone containers, making it possible to bring in water from even distant wells in times of severe water shortage. Plastics are also perfectly matched with the modern information-age uses of cell phones, bank cards, and laptops. And even when mere comfort is at stake, no one can deny plastics are outstanding performers. Synthetic fibers, cousins to plastics, have become so highly developed that even the most die-hard naturalists turn to them to keep warm and dry working out-of-doors on a damp winter’s day, or simply working up a sweat on a crisp cool ski slope.

But plastics, being so inexpensive, run counter to the usual association of good with rare and costly—the snob-appeal factor. Gold is good; silk and satin are good; but what are we to make of plastics, which anyone can own?

Their low cost and versatility have also allowed an unprecedented range of applications. In a free market all market niches tend to get filled, so that plastics have taken on every imaginable form. People’s tastes being as varied as they are, there are differences of opinion on the aesthetic value of some of them. What one person finds fetching, another finds garish—and the material is condemned along with the form given it. The fact that many beautifully designed plastic objects are manufactured has never seemed to provide enough weight to balance the view that associates plastics with aesthetic poverty. Plastics may never shed the guilt-by-association burden, because their low manufacturing cost will always allow the mass production of objects of disputable beauty.

Moreover, the synthetic nature of plastics has come to stand for artificial and not-genuine, with connotations of phony or false. (He is so plastic!) The combined effect of tawdry applications and conflation of synthetic and false has been to color the popular attitude toward plastics.

Some singular voices have even been raised connecting plastics with all that is bad in society—a “malignant force” set loose to wreak havoc. But, in the remarkable breadth of human opinion, countervoices have unstintingly and exuberantly sung their praise. Nylon is not only practical, it’s sexy. Vinyl phonograph records produce the only truly authentic sound. Andy Warhol wanted “to be plastic.”

This book is not about the sociology of plastics, and it is not about the role that plastics play, or do not play, as the cause of, or the reflection of, deep-rooted social, political, cultural, or economic truths. It tells the story of the recent, as yet tentative, emergence of new plastics with characteristics not usually associated with plastic—plastics made from natural, renewable starting materials, plastics that are able to biodegrade totally and completely in an environmentally benign manner.

Not being a plastics industry insider, I am not privy to the long-term plans being worked out in the board rooms of the plastics industry. It is possible that even the movers and shakers of the plastics industry do not know exactly what paths the industry will be taking five or ten years from now. But as a chemist with a thirty-year professional relationship with molecules, particularly the large polymer molecules found in nature, I see these natural polymers coming into their own as starting materials for a new breed of plastics.

If these new plastics make their mark, it will be a comeback, a revival, rather than a totally new appearance, for they have not been completely unknown in the past. Perhaps the closest we have ever come to having a major presence of plastics made from natural polymers was when Henry Ford began a substantial research project aimed at making plastic automobile parts out of soybeans! But his plan was cut short by World War II. Had the soybean venture worked out, we might have had by now a new slang expression, “—or I’ll eat my car.”

The starting point in the story of these new bioplastics is the simple fact that plastics are now so commonplace that they have become an integral part of everyday life. There are personal use items, like the toothbrush, comb, ballpoint pen, and credit card. There are containers, like the jug of milk and the bag that holds the loaf of bread. And there are the wrappings on all those articles we purchase, like drugstore items, clothing, and videocassettes.

Plastic comes in all sizes and shapes. It can be molded, like the comb and toothbrush, or formed into sheeting or films. Some items are only partly made of plastic; others are made entirely of plastic, but of more than one type of plastic, fabricated to make a useful item.

Production of plastics on a very large scale is relatively new. The Dustin Hoffman character in the 1967 movie The Graduate was advised to go into “Plastics!” if he wanted a promising career and a prosperous future. That future is now. In the United States plastics industry over 20,000 facilities produce or distribute raw materials, molds, processing machinery, or products. They employ over one and a half million workers and ship more than $300 billion in products annually.

Past ages of human society have been called the Stone, Bronze, Copper, Iron, and Steel Ages, according to the material most used to fabricate objects. Today the total volume of plastics produced worldwide has surpassed that of steel and continues to increase. Approximately 200 billion pounds (100 million tons) of plastics are produced each year, with over 80 billion pounds a year being produced in the United States alone (fig. 1.1). We have entered the Age of Plastics.

Figure 1.1 Plastics production in the United States

How Do We Use All That Plastic?

The phenomenal rise in the use of plastics is the result of their extraordinary versatility and low cost. They make a good match with the needs of our rapidly growing world population. But if 200 billion pounds of plastics are produced each year, that’s about 40 pounds a year for every person on the planet. What do we do with it all?

Much of the plastic that is produced is used for packaging. In the United States, about 30 percent of the plastic produced each year, over 20 billion pounds, is used for packaging, representing its largest use by far (fig. 1.2). In Western Europe 42 percent of all plastics use is for packaging.

Many people remember items that were previously sold unpackaged in bins but are now packaged individually or in groups of some small, or large, number. The purpose may be to provide added protection, longer freshness, or some other benefit to the consumer; it may be for inventory or some other purpose of the seller.

Figure 1.2 Uses of plastics produced in the United States

Plastic packaging is popular on account of its low cost and performance properties. There are now many forms of it, from plastic shopping bags to different types of plastic loose-fill packaging material, including the peanut-shaped variety.

Approximately one-half of the plastic used in packaging is for containers, such as soft-drink bottles and jugs for milk, water, laundry detergent, and bleach. One-third is in the form of plastic sheeting or film for items like bread wrap and grocery sacks. The remainder is for closures (caps and bottle tops), coatings, and other purposes.

Both flexible plastic packaging and semirigid plastics have been growing in use in food packaging so that now, although paper and paperboard packaging still dominates, plastic food packaging has become second in importance, followed by metal, glass, and other materials. Food and beverage packaging accounts for approximately 70 percent of the more than $100-billion packaging market in the United States and more than half the $400-billion worldwide market.

The popularity of microwave ovens has contributed to the rapid growth of plastic food packaging because they require the use of nonmetal containers. Many plastic packages are now designed to go conveniently from the freezer to the microwave oven, to the dinner table, and then directly to the trash bin.

As plastic packaging has increased, the use of synthetic packaging adhesives has also grown, in order to maintain compatibility. Plastic surfaces are often difficult to bond, the packaging is frequently very flexible, and the processing of packaging materials is typically rapid. Natural adhesive materials made from starch, dextrin, and sodium silicates, although cheaper, have not been able to compete in some packaging markets, and there has been a large increase in the production of synthetic packaging adhesives. Over a billion pounds of synthetic adhesives are used in the United States each year for packaging. We have become a plastics-oriented society partly because we have become a packaging-oriented society.

But plastics are versatile and are used for much more than packaging. Building materials of heavy-duty plastic, often replacing metal and wood, are manufactured in the United States to the extent of nearly 20 billion pounds a year. Consumer products include eating utensils, toys, diaper backings, cameras, watches, sporting goods, personal-hygiene articles like combs and razor handles, and much more. Institutional use of some of these items, like plastic eating utensils in schools and hospitals, makes plastics use for consumer products very large. In the United States over 10 billion pounds of plastic are turned into consumer products each year.

Transportation uses for automobile, watercraft, and aircraft parts total more than 4 billion pounds a year. Furniture accounts for almost 4 billion pounds a year. Electrical components, including wiring insulation, are commonly plastic.

There are many other miscellaneous end uses of plastics, each accounting for a billion pounds or so a year or less. Plastics are used on a large scale for trash bags, which might be called packaging for trash. Around a billion pounds of plastics are manufactured each year for that purpose alone. Industrial plastic sheeting is also used widely. In manufacturing industries there are many plastic machinery components. Plastic materials are used as coatings for paper and cardboard. Hospital equipment, scientific-research equipment, and military equipment all have plastic components.

Agricultural uses of plastics are more important than the scale of production indicates. Plastic ground covers, for example, are used to increase crop yield by as much as 200 or 300 percent. Just as home gardeners use mulch to conserve moisture, raise the soil temperature, prevent nutrient loss, and inhibit proliferation of weeds and insects, farmers use plastic agricultural covers for the same purposes but on a much larger scale. The use of agricultural covers is driven by economics. If the increase in crop yield outweighs the costs of producing and using the cover, the cover has an advantage. The use of plastic agricultural covers on a scale of millions of acres is important for increasing food production for a growing world population, and it is significant in terms of the vast amount of plastics required.

Other large-scale agricultural uses of plastics are for plant containers, binders and twines, irrigation products, netting to protect crops from birds, and temporary covers for storing grain.

There is a constantly growing number of uses for plastics in biomedical applications. They vary from the ordinary, like gloves, masks, gowns, plastic wraps, and coverings, to the more complicated, such as sutures, other wound-closure products, and drug-delivery systems, to the extraordinary, including orthopedic-repair products and other implants. Plastics used for the more complex biomedical applications are expensive and are not produced on the same large scale as the high-volume, low-cost commodity plastics that account for most of the use of plastics.

The use of plastics has grown so remarkably because of the large number of applications that have been developed for them. Plastics have become an important part of modern life and are here to stay. They have, however, raised the question of reconciling convenient living with concern for ecology.

2323__perlego__ch...