Design for Sustainability with Biodegradable Composites

*Dina Fouad and Mahmoud Farag*

#### **Abstract**

Many of the petroleum-based materials and products are causing problems with sustainability of resources and disposal at the end of their lives. Such problems can be solved if biodegradable materials from renewable resources are used in product design. For a material to be fully biodegradable, all its constituents must be biodegradable and should come from renewable resources if it is to be sustainable. Starchplant fiber composites satisfy both conditions. In addition to their environmental benefits, materials from renewable resources can also be economically advantageous in certain applications, such as motorcar and packaging industries. This chapter starts with a review of the characteristics of biodegradable materials and uses case studies to illustrate their use in the design of sustainable products. The concept of design for a life (DFL), in which the material used in making a given product that will biodegrade at the end of its useful life, will also be explored.

**Keywords:** sustainability, design for a life (DFL), biodegradable composites, natural polymers, natural fibers, degradation, economics of sustainable designs

#### **1. Introduction**

Recently, several reviews have been published to report on the advancement in the fabrication and superior properties achieved in biodegradable materials [1–5]. Such growing global notion and urgency toward the need for biodegradable sustainable alternatives to petroleum-based synthetic plastics have stemmed from the increased environmental awareness, depletion of the scarce nonrenewable resources, as well as the implementation of stringent governmental regulations in several countries [5–10]. They mostly emphasized on the suitability of bio-based polymer composites as substitutes for conventional synthetic polymers. The main problem stems from the fact that plastics have become one of the major pollutants of current times. Due to the ubiquity of nondegradable plastics associated with products used in everyday life and the deficiency in creating a proper recycling infrastructure, plastic waste has proliferated over the years and accumulated in landfills and oceans causing severe ecological and environmental problems across the globe [10]. Another concern is the possibility of such waste releasing toxins in landfills and reaching food resources, which has a negative impact on human health [11, 12]. Consequently, a high demand for biodegradable alternatives has arisen in different fields and industries as an attempt to achieve a more environmentally friendly approach in product manufacturing and design [7]. Accordingly, the European bioplastics report published in 2018 has forecasted more than a 20% growth

in the production of bioplastics by the year 2023 [13]. Concurrently, the demand and production of plastics in general continue to rise, where it is expected to reach staggering 540 million tons in 2020, where only 2.2 million tons are estimated to be of bio-based resources [13, 14]. Despite the promising growth rates in the field of bioplastics, comparison demonstrates that the rate of growth is still very small in contrast to that anticipated for traditional plastics. The transition and adaptation of bioplastics is generally impeded by their higher cost of production and lower durability as opposed to their conventional counterparts [8, 9, 15]. Therefore, it is important for the degradable plastic alternatives to be designed so as to offer the same functionality as the original synthetic plastics for the required service life and at a competitive cost [8]. Here, the cost is only justified when the cost of sustainability is taken into consideration and not only that of production [15]. On the other hand, in spite of the challenges faced, several industries such as the packaging, automation, consumer goods, and biomedical fields have shown encouraging implementations of biodegradable alternatives in their plastic-based commodities, taking the necessary preliminary steps towards the commercialization of bio-based and biodegradable plastics [7, 13, 16]. Products that are produced using such materials are designed to biodegrade at the end of their useful life using the design for a life (DFL) approach which is a crucial element in the successful transition to sustainable bioplastics [17]. For instance, a packaging material can start to biodegrade soon after the consumption of its contents with a supplementary benefit of avoiding any harmful contaminants that could have leached to the food content from the synthetic counterparts, which indicates a clear environmental advantage. Ecological and sustainable advantages are also achieved when they are applied for components of automobiles to achieve an eco-friendly design [18]. Thus, in order to achieve a successful implementation of the DFL approach, a thorough understanding of the different biodegradable polymers and composites available is needed along with their properties, methods of production, and degradation to properly evaluate and asses its life cycle and positive impact. This chapter presents an overview on the different types of biodegradable polymers and composites highlighting their main characteristics and advantages. Moreover, the use of the design for a life approach will be elucidated using a case study in the field of automation.

that naturally degrade and assimilate in the environment into water (H2O) and carbon dioxide (CO2) by means of microorganisms [23]. In regard to the biopolyesters, their hydrolysable ester bonds are what make them biodegradable, while for the natural polymers, the process is usually through hydrolysis [7]. Moreover, the means of fabrication are categorized into three main classes: (1) chemical polymerization of monomers originating from biological processes such as in the case of polylactic acid (PLA), (2) chemosynthesis of the polymers in microorganisms such as polyhydroxyalkanoate (PHA), and (3) modification of natural polymers, i.e., starch [5]. **Table 1** summarizes the different typologies used to categorize the different types along with their source and methods of production. Also, characteristic examples of each type are indicated, and their main features highlighted.

Among the most representative of the synthetic polymers are the aliphatic biopolyesters (listed in **Table 1**), PLA, PHA, and polycaprolactone (PCL) [18]. Polycondensation of bifunctional monomers and ring-opening polymerization processes are commonly used to yield high molecular weight polymers [7]. A comprehensive overview of the different chemical synthesis methods used to synthesize them is reviewed in [23]. The prime interest in this class of materials is due to the fact that they exhibit mechanical properties equivalent to petroleum-based polymers such polyethylene (PE) and polypropylene (PP) [19]. A summary of the reported mechanical and physical properties of the bio-polyesters and natural biopolymers in comparison to the polyolefin low-density polyethylene (LDPE) is provided in

Polylactic acid is a high molecular weight, crystalline thermoplastic obtained from the ring polymerization of lactide [20]. It was first synthesized in 1931 by a DuPont scientist and was derived from agricultural products such as corn [22]. The typical glass transition temperature (Tg) falls in between 40 and 70°C, while the melting temperature (Tm) is between 130 and 180°C, as referred in **Table 2**. Additionally, it exhibits high strength, where the average tensile strength is 50 MPa

**Table 3** demonstrates the essential differences between the different biopolymers with regard to their cost, mechanical properties, hydrophilicity, and biodegradation rate. PLA is a hydrophobic polymer due to the methane side group present along the chain's backbone. Thus, it is more resistant to hydrolysis than PHAs, and hence, their biodegradation rate is relatively slow [7]. Moreover, the hydrolytic degradation process needs to be catalyzed at high temperatures, normally in the

**Polymer Tg (°C) Tm (°C) UTS (MPa) ε (%) Degradation time (months) Reference** LDPE 100 98–115 8–20 100–1000 NA [20] PCL 60 58–63 4–28 700–1000 >24 [20, 24] PLA 40–70 130–180 48–53 5–8 12–16 [20, 24] PHA 30–10 70–170 18–24 3–25 1–2 [20, 26] Starch 60–80 — 2.6 47 Bulk [6, 25]

*Physical and mechanical properties of biodegradable polymers compared to non-biodegradable LDPE.*

**2.1 Bio-polyesters: synthetic polymers**

*Design for Sustainability with Biodegradable Composites*

*DOI: http://dx.doi.org/10.5772/intechopen.88425*

compared to 14 MPa of polyolefins such as LDPE.

**Table 2**.

**Table 2.**

**41**

*2.1.1 Polylactic acid*
