**3. Definition, composition, and physical and chemical characteristics of plastics**

The term plastic refers to "a material which contains as an essential ingredient a high polymer and which, at some stage of its transformation into finished products, can be shaped by flow," [31]. However, elastomeric materials (also shaped by flow) are generally not considered plastics [32, 33].

Plastics are mainly produced from non-renewable substances, extracted from petroleum and natural gas [1, 34, 35], or renewable like sugar cane, starch, or vegetable oil or even of mineral origin like salt [36]. The evolution of plastic, correlated with its major strengths, makes it a substitute material, to the detriment of metals, for example [37]. Thus, the increase in plastic, and its multiple applications, place it at the forefront of market share, ahead of traditional materials [38].

The International Organization for Standardization (ISO) [31] recommends the use of the term "macromolecule" for individual molecules, the term "polymer" being reserved for a substance consisting of macromolecules, further stipulating that the term "high polymer" or more generally "polymer" denotes a product consisting of molecules characterized by a large number of repeats of one or more species of atoms or groups of atoms (constitutional units), linked in sufficient quantity to lead to a set of properties which hardly vary with the addition or elimination of a single or a small number of constituent motifs [31]. The denomination of "plastics" comes from the characteristic plasticity property of many polymer materials which can be deformed at will under the effect of temperature (the notion of temperature is relative here: certain plastics are deformable at room temperature) [39]. Thus, most of the plastic materials placed on the market result from complex formulation steps intended to give the macromolecules the desired properties of use. Adjuvants such as stabilizers and additives will be used to limit the degradation of the chains under the effect of heat, radiation, abrasion (antioxidants, mineral fillers, etc.) and give them specific properties (plasticizers, dyes, flame retardants, reinforcements ...) [39].

A main classification of plastics is based on the durability or non-durability of their shapes, or whether they are thermosets or thermoplastics [40]. According to Plastics Europe [36], plastics can be classified into various types. A typology of plastic as well as their applications and benefits are published on the website of this institution, which is an association of plastic manufacturers in Europe (**Table 1**).

#### **3.1 Microplastics**

Jiang et al. [40] note that the degradation of plastic waste generates microplastic (MP) or nanoplastic particles (NP); this division is based on the diameter of the plastic fragments or particles, MP being less than 5 mm in diameter and NP being 1 to 100 or 1000 nm in diameter [40]. The scientific literature on the diameter of plastic particles provides several information and divisions of microplastics. Arthur et al. [41] report when it was reported in 2004, the term microplastics was used to describe fragments of plastic approximately 20 μm in diameter. However, while these early reports referred to truly microscopic particles, they did not provide a specific definition of microplastic. In 2008, the United States National Oceanographic and Atmospheric Agency (NOAA) hosted the first International Microplastics Workshop in Washington and, as part of that meeting, formulated a broader working definition to include all particles. Less than 5 mm in diameter [41]. Other authors consider that particles>5 mm are macroplastics, mesoplastics 5 to>1 mm, microplastics 1 mm to>0.1 μm and nanoplastics as 0.1 μm [5].


**Table 1.** *Type of plastics [plastic Europe – Online].*

*Microplastics and Environmental Health: Assessing Environmental Hazards in Haiti DOI: http://dx.doi.org/10.5772/intechopen.98371*

Microplastics samples are usually sorted into different shapes according to observed morphology. The Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) [42] recommends five general categories of recommends, including fragment, foam, film, line, and pellet. **Figure 1** presents the standardized size and color sorting system (SCS) for categorizing microplastics [43]. It is recommended the original data in these finer subdivisions with the recognition that subdivisions can be combined for ease of harmonizing and comparing data [42].

**Figure 1.**

*The standardized size and color sorting (SCS) system [43].*

According to Crawford et al. [43], the SCS system generates unique codes to process microplastic abundance data, requiring an efficient categorization system. **Table 2** presents a categorization of plastic according to size, while the **Table 3** gives the categorization of microplastics according to morphology.

There are many hundreds of different types of polymer and mixtures of polymer in commercial production, but the market is dominated by: polyethylene (as both


#### **Table 2.**

*Categorization of pieces of plastic based on size [43].*


#### **Table 3.**

*Categorization of microplastics based on morphology [43].*


*Microplastics and Environmental Health: Assessing Environmental Hazards in Haiti DOI: http://dx.doi.org/10.5772/intechopen.98371*

#### **Table 4.**

*Main polymers found in microplastics [32].*

high-density HDPE, and low-density LDPE), polypropylene (PP), polyvinyl chloride (PVC), polyurethane (PUR), polystyrene (PS), and polyethylene terephthalate (PET). These six polymers make up about 80% of plastics production and are likely to form a large proportion of most marine litter (GESAMP, 2019). The most common humanproduced and petroleum-derived polymers found in microplastics are listed in **Table 4**.

According to Lambert, et al. [16], "Microplastic" is an umbrella term that covers many particle shapes, sizes, and polymer types, and as such the physical and chemical properties of environmental microplastics will differ from the primary microbeads commonly used for ecotoxicity testing. In the **Figure 2** is presented the physical and chemical properties of MP, by concentrating particle size, particle shape, surface area and crystallinity, as well as chemical composition, while considering the type of polymer, additive compounds, and changes in surface properties) [16].
