Introduction

This chapter covers broad issues about polyolefins (specifically, polyethylene- and polypropylene-based materials), such as their composition, their growth rates in the plastics marketplace, and their importance in various applications. It explains why polyolefins are important enough to focus on as a distinct segment of the plastics industry, and thus why their additives are the focus of the book. It covers key recent issues with polyolefin plastics use that have been influencing the use of additives, such as their use in packaging and durable applications, their recycling, the new and improved properties that users are demanding from them, and the greater attention they and their additives are drawing from regulators.

Keywords

Plastics; polyolefin; additives; polyethylene; polypropylene; packaging

This brief introduction will cover broader issues with polyolefins (polyethylene (PE) and polypropylene (PP)) that justify this book’s central focus on polyolefin additives. As with forthcoming chapters, this chapter begins by listing some general guiding questions (and the sections in which they are discussed):

1.1 Importance of Polyolefins

Plastics would not be so common in daily life if not for the technologies behind one general family of polymers: polyolefins. Since World War II, daily life in both industrialized and developing countries has become radically changed by just these carefully formulated organic materials. Just a daily trip to the market exposes consumers to the most widespread uses of these polymers in packaging; other, more durable applications often lie hidden behind the scenes.

PE and PP are based on deceptively simple molecular structures, made only from C and H, carbon and hydrogen. PE, the most basic of all commercial polymers, is made of repeating units of –(CH2)–. PP offers somewhat more structural and property variations with its repeating units of –(CH(CH3)–CH2)–.

With PE and PP, products once made from other materials became cheaper and often more durable. Innovative products that never existed before became possible, and affordable, while other products became lighter, brighter, or more user friendly. And food and water could be packaged and transported in new, flexible ways (with even the modest polyolefin water bucket contributing much to a community that otherwise could afford few other industrial products).

The sheer total volume and growth of polyolefins produced reflect their importance. PE and PP make up well over half of the more than 150 million metric tons of thermoplastics demanded worldwide, with PE accounting for nearly two-thirds of all polyolefins used. This consumption is roughly equivalent to 15 kg of polyolefin product per year for each person on earth. And this usage will grow; worldwide PE production alone is expected to rise from about 80 million metric tons in 2013 to around 120 million in 2023 (over a 4% annual increase). So, given this demand for polyolefins and the range of product types available with these versatile materials, it is likely that most people in the world now come into contact with an article made from PE or PP at least once each day. This is made even more likely by all the processes used for forming polyolefins into products: film and sheet extrusion processes of various types, profile and pipe extrusion, injection molding, thermoforming, rotational molding, and blow molding, to name just the most common processes [1-1, 1-2, 1-20].

Polyolefins’ greatest use is in packaging materials, which consume about 69% of all PE and 43% of PP. And now, as a dominant engineering plastic as well, PP has become prevalent in the automotive sector, making up about 60% of the 170 kg of polymeric materials used per vehicle. This includes PP used in thermoplastic olefins (TPOs), complex compounds typically made from PP, an impact-modifying rubber component, and a stiffening mineral filler. Other high volume sectors for polyolefins include consumer goods, construction and infrastructure applications (such as pipe, wood-plastic composites, and TPO roofing membranes), and agricultural film and other films and sheet [1-18].

The production of and demand for polyolefins continue to grow with global PE demand expected to average 4.8% annually and PP demand at 4.5% for the period 2014–2024. However, their growth has shown widely fluctuating annual rates over time. PE’s annual growth rate was over 6% in the late 1990s/early 2000s. This growth then fell below 1% during the global “Great Recession,” but now PE demand is expected, in the United States, to rise back to a 2–3% growth rate over 2014–2019. This will come from new trends in a recovering global economy, with maximum PE production operating rates and new production capacity, plus new food packaging and other applications. PP, fueled by its particular versatility and improved properties, continues to grow ahead of other resins. PP maintained an annual average growth rate of 6–7% since 1980 with annual growth falling off to under 3% in the 2000s. Up to 2.7% demand growth in North America is expected for 2014–2019. PP production capacity has been expanded in the Middle East in recent years, but the pendulum may be swinging back to growing PE capacity in the West instead. In North America, new PP production capacity is expected to reach only about 10% of the output of new PE production capacity (9 billion kilograms added through 2020), due to expanding shale gas supplies, high demand worldwide, and processors switching from PP to PE in applications where they find can cost savings from the switch [1-3, 1-13, 1-14, 1-15, 1-16, 1-17, 1-21].

Meanwhile, both PE and PP growth will be supported by more efficient processing aids, stabilizers, and other additives that are being introduced into the market.

1.2 Importance of Polyolefin Additives

Given their low costs, PE and PP have traditionally been categorized as “commodity plastics.” But this is misleading; in fact, polyolefins have been used for some engineering applications for years. And although they are cheap relative to other polymers on a volume basis, their per-pound prices over the past 20 years have increased to levels higher than even a 3% per year inflation rate would dictate [1-19].

Their properties continue to be improved by the use of additives that are often under-recognized or poorly understood—or even poorly defined. In this book, “additive” will be used generally to refer to any material intentionally added to the base polyolefin resin to influence the resulting compound’s properties. This is a concise paraphrase of a 2011 European Union food contact regulation definition of a plastics additive: “a substance which is intentionally added to plastics to achieve a physical or chemical effect during processing of the plastic or in the final material or article; it is intended to be present in the final material or article” [1-18].

Although the molecular weight and polymer structure of polyolefins can be carefully controlled by advances in polymerization techniques, these advancements don’t account for all of the property improvements in commercial PE and PP grades. Reaction catalyst technologies are critical for providing many desired physical properties and processing characteristics, but they cannot address all the issues polyolefins face during processing and service. And they cannot enhance many of the properties that make polyolefin materials serious candidates for applications once controlled by more expensive engineering plastics. Additive reinforcements such as glass fibers, for example, will likely continue to be the main way PP is strengthened for its most extreme engineering applications.

Meanwhile, markets are driving improvements in low-cost, nonengineering applications of polyolefins such as packaging. But now, just efficiently enclosing a food item or other product is no longer enough; the packaging itself must communicate a product brand’s unique qualities. Better reactor technologies have been heralded as providing high-clarity resins allowing new packaging uses, but new additives are at least as important for creating clarity or subtle effects in color or design that sells the packaged product. As these demands increase, traditional additives will continue to be challenged by new and improved additives technologies.

1.3 Recent Issues in Using Additives

Even though they have been used commercially since only the mid-twentieth century, polyolefins, and thermoplastic materials in general, have reached a certain maturity. Processors and designers are no longer excited by their basic capabilities; instead they ask: “How can I make more effective uses of these materials?”

Consequently, the plastics industry has seen the wall thickness of plastic articles become thinner, though still stiff. The industry has seen greater demands for tougher materials with greater resistance to tearing, puncture, and environmental factors. And it has faced the need for “leaner,” more flexible...