An Overview of Degradable Polymers - ACS Symposium Series (ACS

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An Overview of Degradable Polymers Degradable polymeric materials have attracted a lot of attention in view of current interest in sustainability, recyclability, and environmental responsibility. Because of ongoing R&D activities, a large number of degradable polymers have been reported. For convenience, a summary of common degradable polymers and degradation mechanisms is given in Table 1.

Table 1. Summary of degradable polymers Type

Examples

Mechanism(s)

a. Condensation polymers

Polyesters, polyamides, polyureas, polyurethanes, polyanhydrides

Hydrolysis, microbial or enzymatic action

b. Addition polymers

Addition of pro-oxidant or photo-sensitizer. Use of biodegradable or sensitized comonomers

Thermo-oxidation, photo-oxidation

c. Water-soluble polymers (WSP)

Poly(vinyl alcohol), poly(ethylene glycol)

Microbial action

d. Blends (with natural polymers or WSP)

Starch-based blends, PLA-based blends

Disintegration, ease of oxidation and degradation

1. Synthetic Polymers

2. Natural polymers (biopolymers or agro-polymers) a. Polysaccharides

Starch (& its derivatives), cellulose (& its derivatives), chitin, alginate, hyaluronic acid

b. Proteins

Soy protein, zein, casein, wheat gluten, gelatin. Also derivatives.

c. Lipids

Triglycerides (& its derivatives)

d. Semi-natural polymers

i) Agro-monomers, e.g., lactic acid, 1,3-propanediol ii) Microbial polymers, e.g., PHA

e. Blends of natural polymers

Starch-PLA, starch-PHA, cellulosic esters-PHA

Hydrolysis, microbial or enzymatic action

xiii In Degradable Polymers and Materials: Principles and Practice (2nd Edition); Khemani, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.

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Among the synthetic polymers, poly(lactic acid) (PLA), poly(glycolic acid) (PGA), polycaprolactone (PCL), poly(hydroxyalkanoates) (PHA), and starch-based blends have gained much attention. Among the natural polymers, starch, cellulose, chitin, alginates, proteins, and triglycerides seem to be most cited. There are numerous applications of degradable polymers. A summary is provided in Table 2. The key is the cost/performance of the polymers in use relative to alternatives. At present most of the degradable polymers tend to cost more than commodity polymers. This can be problematical in applications like packaging and housewares but may be less of an issue for biomaterials, pharmaceuticals, and some personal care and agricultural applications.

Table 2. Examples of applications of degradable polymers Category

Applications

Packaging

Food packaging, garbage bags, wrappers

Housewares

Disposable dinnerware, cups, bottles, containers

Personal care

Combs, diaper backing, shampoos

Biomaterials

Medical devices, surgical implants, absorbable sutures, tissue engineering, regenerative medicine

Pharmaceuticals

Controlled release of drugs, homeostatic agents, drug delivery, tablet coatings, hydrogels

Agriculture

Mulch, mulch films, plant covering, pots, bags, trays and containers, controlled release of fertilizers, chemicals, etc.

This book serves as a useful guide to the syntheses, mechanisms, testing, and applications of degradable polymers. It provides a good representation of the state of the art in this field. The editors’ efforts in assembling and editing the contributions from leading workers in this field are much appreciated. (Mention of trade names or commercial products is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer.)

H. N. Cheng Southern Regional Research Center USDA – Agricultural Research Service 1100 Robert E. Lee Blvd. New Orleans, LA 70124, USA

xiv In Degradable Polymers and Materials: Principles and Practice (2nd Edition); Khemani, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2012.