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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.
Downloaded by GEORGE MASON UNIV on November 21, 2012 | http://pubs.acs.org Publication Date (Web): November 20, 2012 | doi: 10.1021/bk-2012-1114.pr002
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.
