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list of additives can be simplified by dividing the types of additives into three groups: functional additives, colorants, and fillers/reinforcements. The most common types of additives used are outlined in Table 2.1 along with typical loadings in the polymer, percent share in global plastics production, market sizes, key examples, and desired effects.

Table 2.1 Classes of plastic additives, typical loadings, and percent share in plastics production.

      Source: “Typical loadings” are the max and min ranges reported by Geyer et al. 2017, Zweifel et al. (2001), Hahladakis et al. (2018), Andrady and Rajapaske (2019), and Ambrogi et al. (2017).

Type	Additive Class	Typical loadings (wt%)	Share (%)	Market size (USD million)a	Examples	Purpose
Plasticizers	Functional	10–70	34	1550	Phthalates, tris(2‐chloroethyl) phosphate	Soften polymer and make more flexible
Flame retardants	Functional	3–25	13	7000	Poly(bromo diphenyl ethers), organophosphorus	Prevent ignition or flame propagation
Antioxidants	Functional	0.05–3	6	5770	Hindered phenols, alkylphenolsb, phosphitesc, lactones, hydroxylamines	To prevent discoloration and degradation during processing, use, and weathering
Heat stabilizers	Functional	0.1–8	5	3630	Dialkyl maleates or laureates and dialkyl mercaptides of tin in PVC formulations to retard HCl evolution during processing	To prevent thermal degradation during processing
Fillers	Fillers	1–50	28	10 000	Clays, silica, glass, chalk, talc, asbestos, alumina, rutile, carbon black, carbon nanotubes	To provide mechanical reinforcement or formulation cost reductions
Impact modifiers	Functional	0.5–30	5	3280	Acrylonitrile butadiene styrene (ABS), acrylonitrile styrene acrylate (ASA)	To increase flexibility and impact strength to meet physical property requirements of rigid parts
Colorants	Colorants	0.25–5	2	37 000	Cadmium, chromium, lead, and cobalt compounds, titanium dioxide, carbon black; organic dyes	To impart a desired color on the finished product
Lubricants	Functional	0.1–3	2	4558	Waxes, oils, long‐chain esters of polymeric alcohols	Allows easier processing of the plastic (i.e., lower temperatures, faster processing times)
Light stabilizers	Functional	0.05–3	1	373	Hindered amine light stabilizers, benzo‐phenone light‐absorbing compounds	To prevent degradation of the plastic upon exposure to light sources
Other (anti‐static, anti‐microbial, etc.)	—	—	4	—	Silver, thiabendazole, aliphatic amines	—
Monomers, catalysts	Unintended Additives	—	—	—	Bisphenol‐A, styrene, antimony	Unreacted monomers or residual catalyst left over from the polymer synthesis

      ^a These are market sizes for all applications, not just in plastics.

      ^b The majority of alkylphenols (APs) found in the environment are degradation products of surfactants, not plastic additives.

      ^c If phosphites are used, the loadings can be higher than the range indicated.

2.2 Functional Additives

      2.2.1 Plasticizers

      Plasticizers are added to plastics to improve their flexibility, durability, and elasticity over a broad range of temperatures while also reducing the glass transition temperature (T _g) and the melt flow. The dissolved plasticizer molecules, not being covalently linked to the polymer backbone (Greco et al. 2010), can migrate freely within the resin matrix. The exact mechanism of plasticization is not fully understood; however, studies demonstrate that strong association of the polymer chains with the plasticizer molecules creates additional free volume in the bulk plastic matrix, yielding a softer and more flexible material (Greco et al. 2010; Ramos‐Devalle and Gilbert 1990).

Relatively high concentrations of plasticizers are required to achieve these desired changes in plastics, accounting for 34% of the total additives used in global plastics production from 2000 to 2014 (Geyer et al. 2017). Phthalic acid esters, or phthalates, are the most widely used plasticizers. Of the reported 8.4 million metric tons of plasticizers manufactured worldwide in 2017, about 65% were phthalate plasticizer used by the poly(vinyl chloride) (PVC) industry (IHS Markit 2018), with di(2‐ethylhexyl) phthalate (DEHP) being the most widely applied phthalates in PVC (Table 2.2). Because DEHP is highly regulated, it has gradually been replaced by diisononyl phthalate (DiNP), diisodecyl phthalate (DiDP), and di(2‐propylheptyl) phthalate (DPHP). In 2015, DPHP represented 57% of plasticizer consumption in Europe (ECPI 2016). However, the high loadings and migration of plasticizers from plastic materials have led to significant concern about the effects of phthalates in the marine environment as early as 1978 (Giam et al. 1978).

      2.2.2 Flame Retardants

Plastics, especially those with a high carbon content, are inherently flammable. For many resins, the most cost‐effective method for increasing fire safety is to blend a FR additive into polymer formulations

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