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Final Report: Scrap Tire Recycling: Convincing Businesses to Integrate Inexpensive, Cutting-edge Technology to Convert Tires Into Various Construction Materials

EPA Grant Number: SU831811
Title: Scrap Tire Recycling: Convincing Businesses to Integrate Inexpensive, Cutting-edge Technology to Convert Tires Into Various Construction Materials
Investigators: Teymour, Fouad , Arastoopour, Hamid
Institution: Illinois Institute of Technology
EPA Project Officer: Nolt-Helms, Cynthia
Project Period: September 30, 2004 through May 30, 2005
Project Amount: $17,132
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity, and the Planet (2004)
Research Category: Pollution Prevention , Pollution Prevention/Sustainable Development

Description:

Objective:

The entry from Illinois Institute of Technology submitted to the EPA P3 Award competition is the result of a project carried out under the Interprofessional Projects Program (IPRO), which has been a unique distinguishing feature of IIT’s undergraduate curriculum over the last decade. The IPRO program engages multidisciplinary teams of students in semester-long undergraduate projects based on real-world topics that reflect the diversity of the workplace. The teams are led by a graduate student and guided by the faculty adviser. Teams include 5-15 students from all academic levels and across IIT professional programs including engineering, science, business and architecture.

The IPRO program gives engineering and technology oriented students a greater appreciation for non-technical considerations, while at the same time instilling in students pursuing non-technical courses of study greater insight concerning the development of rubber recycling technology, which is the focus of this entry. The team was lead by Dr. James Braband, IPRO Program instructor and co-supervised by professors Fouad Teymour and Hamid Arastoopour.

The focus of this project is to develop successful, sustainable technologies that are friendly to the Planet, its People and that are conducive to Prosperity, for the recycle of scrap tire rubber, which is one of the major solid waste environmental hazards facing contemporary society. This is enabled by the combination of two novel technologies that have been the subject of scientific research at IIT for several years. These are the non- cryogenic “solid state shear extrusion” (SSSE) pulverization process, and the process for production of “particulate phase interpenetrating polymer networks” (PPIPN).

Solid State Shear Extrusion (SSSE) is a method of pulverizing rubber and polymeric materials. This technology uses an extruder in which the materials are conveyed and heated slightly to form a continuous film of rubber or polymers, followed by a pulverization section. The pulverization section consists of a cylindrical housing and a screw with an independent driver and cooling provided to both the cylindrical housing and screw to maintain the temperature of the pulverization zone at around room temperature. In the pulverization section, rubber is being exposed to high shear and compressive forces and rapid relaxation of the induced stresses. This results in pulverization. The produced particles have many industrial applications, including water control and retention in agricultural industry, tire recycling, value-added manufacturing of new products, reuse of powder as fillers, and coatings While the fine rubber particles produced from the SSSE process are more suited for recycling than the original chunk rubber, the potential for their reuse is still limited. Most applications involve their utilization as inert fillers in virgin rubber formulations or in other composites. The success of such endeavor is bounded by limits of compatibility of the recycled rubber particles with the matrix material to which it is being added. Even when formed under compressive and/or thermal treatment conditions, the resulting composites will always exhibit a loss of strength and mechanical properties when compared to virgin materials. On the other hand, chemical modification of these particles, leading to the addition of various functional groups to their surface and/or core, not only greatly improves their utility in forming composites, but also opens the door for their utilization in a host of value-added applications, involving structural materials, engineering plastics, metal coatings, indoor and outdoor paints, wastewater treatment and agriculture.

The methodology that we have chosen for production of composites involves Interpenetrating Polymer Networks (IPNs), which are known to result in intimately intermingled composites that eliminate the possibility of macro-scare phase separation. IPNs are often used as compatibilizers of incompatible polymer blends. IPNs are composites formed by the interpenetration of the chains of a particular polymer phase through the molecular interstices of another polymer, which by necessity is crosslinked. The interpenetrating phase can also be crosslinked, in which case the composite is known as a full-IPN, or can be formed as a linear polymer, resulting in what is referred to as a semi-IPN. The fabrication of IPN materials could be achieved in single-step in-situ process in which the concurrent formation of the two polymer phases occurs. However, most often these are produced in a sequential process that produces the interpenetrating phase inside a pre-existing crosslinked matrix phase. By default, when working with a recyclable thermoset one has to resort to the sequential approach for the formation of IPNs. It could be argued that the creation of rubber-based IPNs for the sole purpose of chemical modification of the rubber particles is an excessive approach that unnecessarily wastes the material ending up in the core of the particles. However, we have specifically elected to adopt this approach because of its flexibility in controlling the level of interpenetration, thus creating composites with either a high concentration of the added phase near the surface, a more uniformly distributed composite or any number of micro- structural morphologies in between.

IPNs are generally formed on pre-shaped macroscopic matrix items. Because we are able to economically pulverize the recycled rubber material in the non-cryogenic SSSE into a fine powder product, we have the ability to produce a different type of IPNs. The resulting composite materials are formed as particulate phase interpenetrating polymer networks (PPIPNs), which are suitable for further processing either through reforming into a single continuous phase material or through the use as additives in a variety of liquids, melts, suspensions, emulsions or other solid particulate materials. An attractive feature of this process is its ability to produce either surface modified particles, known as the core-shell morphology, or fully interpenetrated composites, depending on the compatibility of the selected monomers and additives with the rubber matrix.

The emergence of the two new technologies (SSSE — solid state shear extrusion and PPJPN — particulate phase interpenetrating polynomers) at IIT presented the team with a challenging opportunity — developing real market applications that may offer improvements in existing rubber based products or dramatically reduce the cost of an already existing product without compromising quality. Analysis of our options while consideration for the amount of particles available for testing and the time constraints, afforded a decision in the selected application choices. These consisted of two major applications which required U.S. Standard Sieve No. 60 rubber particle incorporation in coatings and sieve No. 40 rubber particle incorporation as agricultural soil amendments.

Different amounts of chemically modified rubber particles were added to coatings to reduce the price providing cheap filler and possibly improving surface qualities like slip resistance, durability and elasticity of the coating. Coatings were to be applied to several different surfaces with the intent of testing adhesion and compatibility. The surfaces were: drywall, concrete panel, stainless steel, and white pine wood.

Unmodified rubber particles are found compatible with water because they are hydrophobic. After chemical modification however, the expansive surface area of the particles are hydrophilic and water can attach and even penetrate (swell) the particle. This provided motivation for mixing modified rubber particles with soil and attempting grow different kinds of plants found typically in our Midwestern region.

It was estimated that if rubber particles could possibly adsorb more water than soil particles then quite conclusively watering could be done le frequently. One conclusion would reveal that this could add value to advantage in regions with water shortage. The other attractive feature of rubber particles is the existence of an elastic behavior; and as an added bonus, many sports facilities already use some form of ground rubber.

This incorporated amendment is often found in silica sand under a carpet-like artificial grass such as FieldTurf® or AstroPlay®. Unfortunately unmodified rubber particles are frequently made airborne on impact resulting in particle adhesion to player’s mouth guards and eyes. The advantages in using modified rubber or mix of modified rubber and soil in sport surfacing would be that real grass could be grown on a shock adsorbing surface, a property that regular soil does not have.

Summary/Accomplishments (Outputs/Outcomes):

Industrial rubber mats (used as simulators for scrap tire rubber) were pulverized via the SSSE process and the resulting powder was sieved to produce particles with sizes 30-39 mesh and 40-59 mesh. A large portion of these particles was chemically modified through PPIPN to make them hydrophilic. These processes as described above have provided hydrophilic rubber particles referred to as “modified particles” hereafter.

Coatings experiment

Coatings have been successfully applied to and evaluated on the following surfaces: drywall , concrete panel, stainless steel, white pine wood. A number of paint products were tested, including the following: Behr Latex (White —hi gloss, White — flat, Red — hi gloss, Red — flat), Silver Metallic, Graham washable paint with no filler, Acrylic garage floor paint and Wood finish.

Agricultural experiment

Three different plants were selected to be introduced in varying soil/modified rubber mixes and these included: Kentucky Blue Grass and Tall Fescue (mixed in equal proportions), Soybeans and Brassica Rapa. The grass mixture was selected based upon the selection of the two hardiest of the twelve species typically germinated and found in turf applications in the cool climates of the Midwest. Capable of withstanding poor soil and lacking moisture content, these varieties offered the teams an opportunity to visually record the following behaviors of the grass: root density, water retention, vitality, and surface rebound capacity. Soybeans once thought of for its Japanese origins are now found frequently across the Midwest region. However, more recently, Wisconsin agricultural growers have turned to producing these heavily sought legumes as a significant source of natural proteins. Although known to grow well in the clay-like and silty soils, Soybeans need a large phosphate supply for growth arid since our results revealed no germination — this was fairly typical. Brassica Rapa or Yellow Field Mustard is known to be a Wisconsin fast growing plant that is widely used in agricultural experiments because of its short, but complete life cycle. All plants are known to be available to the general public and at reasonable prices.

Experimental Design

Constants:
Number of plants: 3 (Brassica Rapa, Soy beans, Kentucky Blue Grass+Tall
Fescue mix)
Fixed % of second monomer in rubber particles (i.e. Fixed IPN)
Identical watering schedule for each pot
Identical Light exposure (intended)

Manipulated Variable
Amount of rubber particles in soil (0%, 33%, 66%, 100% - by mass)

Measurable Variables
Time of penetrating the soil surface (time)
Height of plant/grass as a function of time (cm) — periodic data collection

Detailed results, graphical representation and discussion are found in the submitted report.

Conclusions:

The team has concluded that more research should be done in all of the proposed applications. If modified particles are incorporated in sport surfacing, adding nutrients to the soil/rubber mixes should be studied to provide the optimum grass density. Powder coatings are still to be investigated and the surface modification technology provides an unlimited array of functional groups that could be chemically attached to a particle surface to bind with virtually any powder coating resin. Modified particles provided an attractive decorative finish to latex paint without significantly compromising the quality of the coating and in the case of secondary layer of paint, there was no compromise at all.

The goal of the current project was to create applications for the chemically modified rubber particles produced from scrap tires via patented SSSE process and possibly evaluate the market potential of some of those applications. The benefits of implementing such technologies on a large scale are obvious. The raw material for the processes is scrap tires which are relatively economical and readily available - currently stacked in landfills. If more tires are used toward higher value applications similar to the ones investigated in this project, a rapidly decreasing volume of tires will be land-filled which would result in a smaller risk of toxic fires, mosquito spread diseases and fewer emissions from the tire derived fuel.

Proposed Plan for Phase II:

Based on the findings of Phase I, the proposed specific objectives for Phase II are:

Supplemental Keywords:

INTERNATIONAL COOPERATION, Sustainable Industry/Business, Scientific Discipline, Waste, RFA, Technology for Sustainable Environment, Sustainable Environment, Chemical Engineering, Chemistry, cleaner production/pollution prevention, Municipal, Engineering, reuse, tires, scrap tires, solid state shear extrusion, recovery, waste recovery, municipal solid waste landfills, recovered materials, recycling, hazardous waste, innovative technology, pyrolysis, municipal waste, pollution prevention, disposal

Progress and Final Reports:
Original Abstract

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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