A Case Study in Post-Consumer Carpets

Identification and Specification of Recycled Materials for Use in New Products:
A Case Study in Post-Consumer Carpets

Deanna Hart, Chris Hendrickson, Lester Lave, and Francis McMichael
Green Design Initiative
Carnegie Mellon University

Introduction
The fear of overflowing landfills in the Northeast United States and the lure of value in waste materials inspired municipal solid waste management recycling programs. Across the nation, millions of Americans separate aluminum cans, newspapers, glass and plastic bottles from the waste stream. New attention is being focused on other consumer goods such as appliance, computers, and construction materials. While the separation and collection of the materials is widespread, returning the materials back into new products has not been prevalent. Designers and manufacturers are wary of the recycled materials in many cases due to poor quality, unreliable quantity, and high cost compared to virgin materials. Plastics present an especially difficult problem due to light weight, inconsistent labeling, and intensive separation requirements. Businesses cannot afford to spend the time and money investing in materials that are more costly and result in a less reliable product. The problem facing today's engineers is how to better prepare recycled materials so that manufacturers have more confidence in substituting them for virgin materials.

Post-Consumer Carpet Waste

Approximately five billion pounds of carpet are replaced with new each year in the U.S. This could translate into an abundant supply of recycled plastic material for manufacturers if processed correctly. Carpet is composed of several different plastics (nylon, polyester, polypropylene), natural fibers, clays, chalks, and adhesives. The materials are constructed into a tightly woven and bound matrix built to last for an average of 10 years. This combination and arrangement of materials makes economically sensible recycling an arduous task. Several carpet producers are working toward recycling carpets, and one breakthrough was accomplished by Monsanto Chemical Company. Monsanto has patented a process that recycles an entire carpet without prior separation of the components resulting in a mixed plastic similar to nylon.

Methodology

Using the Monsanto recycled carpet plastic (RCP) material as a test subject, a model of material identification and specification was developed. The method is intended to aid designers and manufacturers in replacing virgin materials with equivalent recycled materials. Knowing the material properties and fractions of a particular constituent in a recycled material, one can estimate the resulting properties of the recycled material. The new material can then be compared to similar virgin material specifications and proper applications for the material can be found. In addition, the economics of recycling are considered. Advances in marketing recycled materials through exchanges and improved reverse logistics are being examined. The research combines the issues of engineering, economics and the environment.

RCP Results

Results from working with the RCP were informative. The table below compares several properties of the material with other plastics and other classes of materials. The material is an engineering plastic with excellent properties for a variety of applications. Current research is looking into such uses as telephone poles, mechanical bearings, and roadway appurtenances. A higher quality plastic may be formulated by removing more dirt and sand prior to processing, or by mixing the material with pure nylon resins.

Young's Modulus Yield/Fracture Stress Elongation Specific Gravity

kpsi GPa psi MPa %

Recycled Carpet Plastic 404 2.8 5,700 39 3 1.37

Nylon 6 (50% Relative Humidity) 174 1.2 6,000 41 290 1.13

Nylon 6/6 (Dry) 406 2.8 12,000 83 60 1.14

Nylon 6/6 (50% Relative Humidity) 174 1.2 8,500 59 300 1.14

33% GFT ([1]) Nylon 6/6 (50% Relative Humidity> 800 5.5 16,000 110 4 1.32

Polypropylene 218 1.5 4,800 33 50 0.90

ABS 305 2.1 6,000 41 20 1.04

ABS 305 2.1 6,000 41 20 1.04

HDPE 116 0.8 4,000 28 300 0.96

Steel (structural) 29,000 200 36,000 250 23 7.86

Concrete (high strength) 4,500 20 -- 40 ([2]) -- 2.32

Wood (Douglas fir) 1,900 13 -- 50 ([2]) -- 0.47

[1] Glass filled and rubber toughened
[2] Compression Stress

For additional information contact

Lester Lave/Deanna Matthews
Phone: (412) 268-8837/(412) 268-9170
Internet: lave@andrew.cmu.edu/dhm@cmu.edu

Financial Support

Green Design Initiative of Carnegie Mellon University
IBM Environmental Research Program
National Science Foundation
Monsanto Chemical Company

	Young's Modulus		Yield/Fracture Stress		Elongation	Specific Gravity
	kpsi	GPa	psi	MPa	%
Recycled Carpet Plastic	404	2.8	5,700	39	3	1.37
Nylon 6 (50% Relative Humidity)	174	1.2	6,000	41	290	1.13
Nylon 6/6 (Dry)	406	2.8	12,000	83	60	1.14
Nylon 6/6 (50% Relative Humidity)	174	1.2	8,500	59	300	1.14
33% GFT ([1]) Nylon 6/6 (50% Relative Humidity>	800	5.5	16,000	110	4	1.32
Polypropylene	218	1.5	4,800	33	50	0.90
ABS	305	2.1	6,000	41	20	1.04
ABS	305	2.1	6,000	41	20	1.04
HDPE	116	0.8	4,000	28	300	0.96
Steel (structural)	29,000	200	36,000	250	23	7.86
Concrete (high strength)	4,500	20	--	40 ([2])	--	2.32
Wood (Douglas fir)	1,900	13	--	50 ([2])	--	0.47

Identification and Specification of Recycled Materials for Use in New Products: A Case Study in Post-Consumer Carpets

Introduction

Post-Consumer Carpet Waste

Methodology

RCP Results

For additional information contact

Financial Support

Identification and Specification of Recycled Materials for Use in New Products:
A Case Study in Post-Consumer Carpets