Concept of Biodegradability

The concept of biodegradation is, at least superficially, a simple one. A compound is degraded by biological mechanisms and so is removed from the environment. The practice of biodegradability is less certain, however, as evidenced by the number and variation of the tests available. The relationship between test results and actual environmental persistence is well-established for some classes of compounds, for surfactants as an extensively investigated example. For the majority of other materials, however, no such link has been established. 

The use of biodegradable polymers provides another promising path [RUT 04]. The concept of biodegradability is often used incorrectly (sometimes even to justify action in sustainable development) and should be precisely defined. We will read about this subject in the study by Guy Cesar (see Chapter 14). 

The concept of biodegradable synthetic polymers was first proposed in the 1960s as a potential solution to the problem of plastics litter. This was initially welcomed by environmentally aware public, particularly in the USA, since it was perceived to be a possible solution to the landfill problem. Packaging producers in collaboration with corn growers were quick to respond to the public mood by adding corn starch to polyethylene. Carrier bags made from this material were claimed, without experimental evidence, to be biodegradable but the... 

In this contribution, we will successively recall the interest and the limits of biopolymers and of artificial biopolymers with regard to temporary therapeutic applications, degradable polymeric compounds being unsuitable to uses as biostable devices. However, we will first recall the problons raised by the concept of biodegradation and the use of temporary therapeutic applications, with the aim of showing that, in therapeutic applications, it is the fete of the device that is important and not its degradability nor its biodegradability. 

Narayan, R. (2009) Fundamental Principles and Concepts of Biodegradability - Sorting through the Facts, Hypes, and Claims of Biodegradable Plastics in the Marketplace. BioPlastics Magazine (Jan.). 

Narayan, R. (2009) Fundamental principles and concepts of biodegradability - sorting through the facts. 

In this chapter, we have discussed polymer stmcture at the level of the repeating unit. The repeating unit not only has a specific chemical structure but also acts as the source of interaction at the molecular scale. With respect to this, now we will be introducing the concept of biodegradable polymer blends. A polymer blend is classically defined as a physical mixture of two or more polymers, which occurs on a macro scale. We are now going to also consider the science at molecular/nanometre scales, ie, taking polymer repeating unit into account rather than entire polymer chains. For the purposes of this book, the definition of a polymer blend is as follows ... 

This chapter describes the historical development of polymers and the basis of their classification. Based on their origin and mode of synthesis, biodegradable polymers are categorized into various classes. The structure, chemistry, biocompatibility, and biodegradability of these biodegradable polymers are discussed and, at the end of the chapter, their applications in pharmaceutical and medical fields are summarized. The discussed content will provide readers with an insight into the basic concept of biodegradable polymers and their role in everyday life. 

For several years, there has been considerable debate and controversy on the definitions of biodegradable plastic (e.g. at International Workshops on Biodegradable Plastics, Toronto 1989, Tokyo ISBP 1990, Montpellier 1991, Osaka 1993, and elsewhere). While the concept of biodegradability is broadly accepted by many, most of the debate has focused on reducing the broad concept with all its ramifications to a narrow statement, which tends to be accepted by very few. 

The most often used predictive models for biodegradation have been classical QSARs, in which a number of chemical and physical properties, molecular descriptors or substructures have been used to develop predictive models of biodegradability. In principle, QSARs can be used to predict biodegradation rates provided either that global molecular properties are adequate to describe biodegradation or that congeneric subsets of tested molecules can be assembled that are suitable for such study. Unfortunately, the poor reproducibility of experimental data often prevents the development of quality quantitative relationships. As a result, most of the QSARs described in the literature address the more qualitative concept of biodegradability (fast or slow) rather than the calculation of rate constants. 

The concept of using biodegradable materials for implants which serve a temporary function is a relatively new one. This concept has gained acceptance as it has been realized that an implanted material does not have to be inert, but can be degraded and/or metabolized in vivo once its function has been accompHshed (12). Resorbable polymers have been utilized successfully in the manufacture of sutures, small bone fixation devices (13), and dmg dehvery systems (qv) (14). 

The concept of fibrous polymer formulations was extended to the delivery of aquatic herbicides (56). Several herbicides including Diquat, Fluridone, and Endothal were spun into biodegradable poly-caprolactone. Monolithic fibers and a modified monolithic system were produced with levels of herbicide from 5 to 60% by weight. Laboratory and field trials showed efficacious delivery of the active agent. Fibers provided both targeted localized delivery and controlled release of the herbicide to the aquatic weed. 

Hydrolysis of particulate substrates produces readily biodegradable substrate for the biomass (cf. Figure 5.4 and Section 3.2.3). The kinetics of the hydrolysis, following the concept of the activated sludge model one, is described in Section 2.2.2. The following interpretation of hydrolysis of wastewater in a sewer is considered particulate substrate is available in the bulk water phase, and biomass in the bulk water and biofilm—assuming a reduced activity in the biofilm—is taken into account. Under these conditions, the rate of hydrolysis, rhydr, for each of the hydrolyzable fractions, n, is as follows ... 

Data vary widely between sources, depending on the concept of environment-friendly plastics, a certain confusion between consumption and production capacity, and the optimism of the forecaster. In any case, biodegradable polymers are speciality materials that currently represent less than 0.1% of the total plastics, reaching, perhaps, 1% by about 2020. 

The interest in cleavable surfactants has increased rapidly in recent years and the topic has been covered in review papers during the last decade [1-4]. This chapter begins with a relatively thorough discussion about the incentive for hydrolyzable surfactants, continues with a discussion about biodegradation of surfactants, which is important for understanding the concept of hydrolyzable surfactants, and then gives an account of the development of hydrolyzable surfactants with an emphasis on recent results. 

A third and more recent example of where readily biodegradable surfactants have replaced surfactants that are more long-lived in the environment is the taking over of the market for textile softener surfactants by the ester quats from the stable quats. This transition is still in progress today but for several years the big soapers all base their softener formulations for the US and Western Europe markets on ester quats instead of traditional, stable quats. The change from stable quats to ester quats is probably the best example of the concept of introducing a cleavable bond in a given surfactant structure because the two types of products are very similar in structure and physical chemical charac-... 

Low viscosity poly(a-olefins), e.g., 2 and 4 cSt, can be classified as relatively biodegradable in aqueous systems as defined by the CEC L-33-A-93 test however, this does not mean that all poly(a-olefins) are biodegradable. The concept of biodegrability is very difficult to define. The extremely low water solubility of poly(a-olefins) decreases the available surface area for bacterial degradation. If high biodegrabilities are required, linear polyol esters tend to be used. 

Biodegradation test methods By using the test method summaries of Table 7.1, explain the differences in concept of CEC and Close bottle test. Why the presence of additives (nitrogen and phosphorus excluded) in the lubricants is known to have a significant effect on the rate of biodegradation ... 

---