20. Choosing Additives for Sustainability

20 Choosing Additives for Sustainability The conclusion of this book relates to a topic about 20.1 Factors That Make which the entire plastics industry and all end users of Polyolefins Sustainable plastic resins and products are being challenged to confront and address: the sustainability of plastic In a broad view of sustainability, polyolefins materials. could be credited with sustainable characteristics of With the polyolefins, polyethylene (PE) and various kinds, in comparison to those of alternative polypropylene (PP), being by far the most visible materials that might be used for similar products. polymers in everyday life, and especially because Although associated with waste and littering in the they are used so often for “single use” packaging, public discourse, their production, use, and end of readers who use polyolefins cannot avoid ques- life do have some positive “green” aspects: tions about the “green’” nature of the materials— whether the arguments emphasize the materials’ 1. PE and PP are based on relatively simple recyclability (as opposed to their being often lit- molecules, and the energy used in their tered) or their efficient production and uses (when production is relatively low compared to compared with alternative materials such as paper, other polymers. And when considering a metal, or glass). common application like shopping bags, their Considering their property changing roles, addi- production energy is low in comparison with tives are important factors in arguments about what alternatives like paper bags. makes a polyolefin material or application sustain- 2. Polyolefins, especially when compounded to able.Theargumentshavetodowiththeireffectson be durable using additives, offer energy and the materials’ production, use, recycling, and disposal material savings in use. The low-density mate- phases—with these last two phases now becoming rials are good for many automotive parts, more complicated to address by the introduction of making cars lighter and more fuel efficient. additives for promoting polyolefin biodegradability. They provide inexpensive ways of packaging Thus this chapter will address a few key questions in food, maintaining its shelf life a long time and broad ways, while using real-world examples as helping to minimize food waste. And more illustrations: and more in building and construction, polyolefins are used to seal up buildings, reducing • What factors make a polyolefin (PE- or PP-based) heating and cooling loads. Polyolefin film material sustainable? (Section 20.1) wraps and thermoplastic olefin (TPO) roof • What are the characteristics of a sustainable membranes block air leaks and keep out water, polyolefin additive?(Section 20.2) while PP solar shingles produce energy. • What are some innovative examples of “green” 3. Polyolefin polymers are nontoxic and rela- uses of additives in PE and PP materials? tively inert and durable. This makes them safe (Section 20.3) choices for applications that require a shelf life or that contact food or drugs or the human • And what about additives that are said to make body. Their engineering durability is evident in polyolefins biodegradable? (Section 20.4) applications like TPO automotive bumper fas- • Finally, what are some things to keep in mind cia and in wood-plastic composite decking— when choosing additives in terms of sustain- which, now used for at least one-third of ability? (Section 20.5) all decking, does not need to be replaced as Additives for Polyolefins. DOI: http://dx.doi.org/10.1016/B978-0-323-35884-2.00020-X © 2015 Michael Tolinski, Published by Elsevier Inc. 183 184 ADDITIVES FOR POLYOLEFINS often as wood, and is a potential end use for chemical additive may require multiple synthesis recycled plastic and waste wood. (However, steps, each creating atoms that are not present in the polyolefins’ durability makes them persistent final additive. in the environment when littered.) Less Hazardous Chemical Syntheses and Design- 4. Polyolefins’ durability and thermoplastic nature ing Safer Chemicals: These two principles are about also mean that they are among the most- minimizing toxicity in the synthesis method of the recycled plastics. Rigid polyolefin containers additive (which ideally should use or create nontoxic are regularly collected and recycled, and bags or low toxicity substances) and in the final additive/ and wraps (usually made from polyolefins) plastic product (which should be nontoxic). A plant- have been growing in prevalence in the recy- based fiber would seem to fulfill both of these cling stream over the last 201 years—more so principles well, for example, unlike some chemically than most other commonly recycled materials. complex additives like halogenated flame retardants. If anything, their recyclability is now being Use of Renewable Feedstocks: A relatively endangered by their success and versatility. straightforward goal, this principle emphasizes the New polyolefin grades, structures, and addi- use of raw feedstock materials that are based on tives are making it harder for recyclers to dif- renewable resources, when possible. With additives, ferentiate and separate plastics in the recycling an interesting conundrum involves whether mined stream by resin type—with products like clari- mineral fillers that are abundant and relatively inert fied PP packaging resembling PET or other have a natural character that makes them somewhat clear plastics [20-12]. “green,” even though they are not technically biologically renewable. Design for Degradation: This principle will be covered at the end of this chapter. It concerns 20.2 Characteristics of not just the biodegradability of additives at the end Sustainable Polyolefin Additives of a product’s lifecycle but also the effects of degradability-promoting additives used in polyolefins Again, taking a broad view of the concept of that allow them to disintegrate to some degree after dis- “sustainability,” we might describe a “sustainable posal. This principle also concerns other end-of-life additive” simply as an additive that helps a polyole- options like recycling, and how additives can help or fin meet one or more of the above goals more hinder that. effectively and efficiently. But it is a worthwhile Incorporating the above principles into a visual exercise to look for a deeper conceptual framework aid is one way to prioritize additive selection in with which to talk about additives specifically. term of sustainability. Here an “inverted pyramid” One framework to consider is the “Principles of (technically a triangle) is offered in Figure 20.1 to Green Chemistry,” developed in the 1990s by P.T. show which additives in the future should be sought Anastas and J.C. Warner for their book Green more than others in terms of sustainability; those at Chemistry: Theory and Practice. Although their 12 the top tend to satisfy all or most of the above principles were formulated mainly for the chemical principles; those at the bottom, the opposite. The industry, some of them are helpful when discussing area differences in the different sections emphasize additives and sustainability [20-10]. the relative prevalence of use that should be pur- These principles should be read keeping ideas in sued for each category. mind about the additive’s production, its use in the Arguing for the placement of an additive on this plastic product, and its end-of-life influence on the graphic can be tricky, however. For example, glass polyolefin plastic. Here are a few principles that fiber (at the middle of the chart) can increase strength- can be made relevant to polyolefin additives: to-weight of parts ratios efficiently and is chemically Atom Economy: Under this principle, the material nontoxic, but glass fiber can be unpleasant/hazardous used for the production of an additive should be maxi- to handle in production, and glass-filled compounds mized in the additive itself. Thus an additive like a do not fit easily into conventional recycling streams. mineral filler could be seen as relatively efficient to Admittedly, the “toxic additives” at the bottom of the produce (nearly all of its raw material’s “atoms” are chart do raise their own contradictions; for example, used in the final product), while a complicated halogen-based flame retardants (FRs) are less favored 20: CHOOSING ADDITIVES FOR SUSTAINABILITY 185 Plant-based fibers/fillers/compounds, additives recycled from nontoxic waste, biocompatible additives Easily mined/synthesized simple, inert minerals (e.g., CaCo3) Less abundant minerals, refined metals, glass, nanofillers Complex organic Compounds Environmental Toxic sustainability/ add’s desire volume of use Figure 20.1 “Inverted pyramid” of sustainable additives. “Greener” additives are nearer to the top. Based on Ref. [20-1]. for their chemistry, but they are more effective than of their sensitivity to heat and moisture and incom- other FRs (saving more human lives in fires, poten- patibility with conventional recycling. So trade-offs tially) and require lower loadings, and thus less mate- must be considered when evaluating any additive in rial usage and thus less mass, than other FRs. terms of sustainability. Figure 20.1 is not meant to One could argue that basic mineral fillers are rela- oversimplify the process, but rather to serve as tively sustainable—when they are abundant, efficiently starting point. and safely mined, inert and nontoxic, and not rare or easily depleted. There can even be questions about some mineral fillers’ “renewable” nature. For example, 20.3

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