Adhesives Magazine

The Emergence of Green Chemistry

April 1, 2006
This article examines how these trends are likely to impact the future formulation of both adhesives and sustainable materials that can be used to formulate environmentally friendly adhesives.



The new framework for Responsible Care is based on ISO 14001 and is meant to aid companies in considering initiatives such as green chemistry as they pursue R&D on new product lines, or reevaluate existing products and processes. Green chemistry, also called sustainable chemistry, was formally defined at the Environmental Protection Agency a dozen years ago with the aim of preventing pollution through better process design, rather than by managing emissions and waste. Green chemistry provides a set of 12 principles that provide a framework for chemists and engineers to design products and processes with little or no impact on the environment.

12 PRINCIPLES OF GREEN CHEMISTRY

1. Prevent waste. Design chemical syntheses to prevent waste, leaving nothing to treat or clean up.

2. Design safer chemicals and products. Design chemical products to be fully effective with little or no toxicity.

3. Design less hazardous chemical syntheses. Design syntheses to use and generate substances with little or no toxicity to humans and the environment.

4. Use renewable feedstocks. Use raw materials and feedstocks that are renewable rather than depleting. Renewable feedstocks are often made from agricultural products or are the wastes of other processes; depleting feedstocks are made from fossil fuels (petroleum, natural gas or coal) or are mined.

5. Use catalysts, not stoichiometric reagents. Minimize waste by using catalytic reactions. Catalysts are used in small amounts and can carry out a single reaction many times. They are preferable to stoichiometric reagents, which are used in excess and work only once.

6. Avoid chemical derivatives. Avoid using blocking or protecting groups, or any temporary modifications, if possible. Derivatives use additional reagents and generate waste.

7. Maximize atom economy. Design syntheses so that the final product contains the maximum proportion of the starting materials. There should be few, if any, wasted atoms.

8. Use safer solvents and reaction conditions. Avoid using solvents, separation agents or other auxiliary chemicals. If these chemicals are necessary, use innocuous chemicals.

9. Increase energy efficiency. Run chemical reactions at ambient temperature and pressure whenever possible.

10. Design chemicals and products to degrade after use. Design chemical products to break down to innocuous substances after use so that they do not accumulate in the environment.

11. Analyze in real time to prevent pollution. Include in-process real-time monitoring and control during syntheses to minimize or eliminate the formation of byproducts.

12. Minimize the potential for accidents. Design chemicals and their forms (solid, liquid or gas) to minimize the potential for chemical accidents, including explosions, fires, and releases to the environment.



Green chemistry is still a new and emerging concept in the chemical industry. It has been accepted as fact that pollution is inevitable with growth and progress. Proponents of green chemistry emphatically state that pollution and progress are not synonymous.

One of the 12 principles of green chemistry is the use of renewable feedstocks. Many in the chemical industry are skeptical that petroleum feedstocks will ever be successfully replaced with biomass-derived feedstocks.

"The stone age did not end because the world ran out of stones, and the oil age will not end because the world will run out of oil," Environmentalist Amory Lovins, CEO of the Rocky Mountain Institute, wrote in The Economist magazine in 1999.

A four-fold increase in the price of oil since the mid-1990s may be the impetus for moving the chemical industry into a post-petroleum era. The evolution could be fueled by both supply anxiety and the push for more environmentally friendly products. The consensus opinion is that the new era will be characterized by the chemistry of natural products. The first wave of renewable products is slowly replacing petroleum-based raw materials in large commodity markets such as plastics, fibers and fuels. These products come in direct contact with consumers and are marketed as "green" products. The next wave of products will be specialty materials sold primarily to industry. The main drivers for their acceptance as replacements for petrochemicals will be price and performance. Renewable chemicals are making inroads in some basic categories, like solvents, adhesive tackifiers and dispersants for coatings, because they are meeting price and performance criteria.

Patricia A. Nugent, program director for Dow Ventures, is quoted in C&EN: "Dow is not primarily looking to stamp the word `green' on coatings labels. Rather, the goal is to develop an all-around superior product. It is a whole new feedstock for us that gives us the opportunity to bring wholly new materials into the marketplace." Today, raw materials are available to the adhesives, inks, lubricants and fuels industries made from renewable raw materials like pine chemicals, oil seeds, soybeans, and citrus crops.

Table 1

TODAY'S TOP ENVIRONMENTAL CONCERNS

Public perceptions and government actions are largely influenced by the agendas of environmental activist groups. Public perceptions shape activist groups' agendas. Thus, environmental priorities identified by the public and these groups have a profound impact on the development, manufacture, and marketing of chemicals and adhesives. A survey of the most well-known and recognized environmental groups provides insight to the initiatives likely to shape environmental policy in the next decade. The most commonly cited priorities by the most well-known groups include clean air and water, global warming, control of toxic chemicals, and protection of forests (see Table 1).

In October 2004, the Sierra Club polled online subscribers to find out what issues they would want covered in the upcoming presidential candidate debate. The top issues identified in this poll of registered voters were global warming, energy policy, protection of wild lands against oil and gas exploration, mercury pollution, and stricter enforcement of existing environmental laws. The Center for Strategic and International Studies and the Massachusetts Institute of Technology identified the top five global issues on sharing the planet: global warming, biodiversity and ecosystem loss, fisheries depletion, deforestation, water deficits, and maritime pollution. Many of these issues are reflected in the goals of the 2003-2008 EPA strategic plan.

IMPACT ON THE ADHESIVES INDUSTRY

Environmental trends and regulations are shaping programs and influencing product development in the adhesives industry. Green buildings and architecture, renewable raw materials, reduction of volatile organic compounds, and lifecycle considerations (recycling requirements) are the primary environmental drivers in the adhesives industry.

In pressure-sensitive tapes, the major environmental concern is from the formation of the adhesive layer on the tape backing. Early PSAs, such as low-viscosity natural rubbers and rosin resins, were coated from a variety of organic solvents. Typically, solvents were exhausted to the atmosphere. Since the 1970s, regulations have restricted the quantity and types of emissions for such processes. A consequence of increasingly restrictive emission regulations has been the development of pollution- prevention products and processes. This explains the rapid growth of hot-melt pressure-sensitive adhesives based mostly on styrenic block copolymers. These products require no solvents and use much less energy on a lifecycle basis. Emerging technologies are aimed at addressing deficits of current hot-melt formulations. UV-crosslinkable acrylates, for example, have better adhesion and wider application temperature windows than incumbent hot-melt PSAs.The presence of "stickies" in recycled paper streams is an example of a specific environmental need responsible for next-generation adhesive development. The problem with "stickies" is summarized by J.S. Guo, et al, in the October/November 2002 issue of ASI Magazine. Recycling paper mills have four basic unit operations: pulping, screening, centrifugation and flotation. When pressure-sensitive adhesives are present in the paper-recycling stream, they break into small particles and disperse in the recycled pulp. The glass-transition temperature, density and weight of dispersed adhesives often make it very difficult to remove them through the standard recycling process. If the contaminants remain high at the end of the recycling process, the "stickies" in the recycled pulp can cause the paper web to tear and shut down the machine. Companies like Solutia, Springfield, MA, responded to this trend by developing both hydrophobic and hydrophilic adhesives that are "benign" with respect to their impact on paper recycling.



Table 2
The flooring and carpet adhesive business is directly impacted by the emergence of programs that support a trend toward more environmentally friendly buildings. The Leadership in Energy and Environmental Design (LEED) Green Building Rating System® is a voluntary, consensus-based national standard for developing high-performance, sustainable buildings. Members of the U.S. Green Building Council, representing all segments of the building industry, developed LEED and continue to contribute to its evolution. Several types of buildings are covered in the LEED program, but the section of most interest to the adhesives industry is LEED-NC, which pertains to new construction and significant remodeling projects.

Buildings in the United States account for:

  • 36% of total energy use and 65% of electricity consumption
  • 30% of greenhouse gas emissions
  • 30% of raw materials use
  • 30% of waste output (136 million tons annually)
  • 12% of potable water consumption


LEED-NC is a system for designing, constructing and certifying the world's greenest buildings. If a building can claim enough credits under the LEED rating system, it qualifies to be certified as a green building. The sections of LEED-NC with specific relevance to the adhesives industry include the following.
  • Materials and Resources - Credit 4: Recycled Content
  • Materials and Resources - Credit 6: Rapidly Renewable Materials
  • Indoor Environmental Quality - Credit 4: Low-Emitting Materials
  • Indoor Environmental Quality - Credit 5: Indoor Chemical and Pollutant Source Control

Materials claiming credit under LEED require third-party evaluation and documentation of content and emissions analysis. Independent laboratories like Greenguard Environmental Institute (GEI) are developing programs to help adhesive producers certify products as "low-emitting." Greenguard certification is a tool for architects, designers and builders who want to locate and purchase off-the shelf, low-emitting products for indoor environments.

The Carpet and Rug Institute (CRI) also has a program that seeks to improve indoor air quality. Adhesives are used more often in commercial settings to adhere carpet to the floor. CRI has instituted a testing program to identify low-volatile-organic-compound floor-covering adhesives. The program tests for chemical emissions using an independent laboratory that specializes in indoor-air-quality testing. Adhesives that meet the emissions criteria are allowed to display the program's green-and-white label.

Table 3
Tested adhesives fall into a number of categories: latex multi-purpose floor adhesive, pressure-sensitive floor adhesive, vinyl-backed floor adhesive, latex seam adhesive, vinyl-backed seam sealer, cove base adhesive, "tackless" cushion adhesive and contact adhesive. Table 3 lists the criteria for the adhesive testing program based on a maximum emission factor.

The Farm Security and Rural Investment Act (FSRIA) of 2002 provides for development of a preferred procurement program for biobased products under which federal agencies are required to purchase biobased products. The United States Department of Agriculture (USDA), which administers this initiative, has created the Federal Biobased Products Preferred Procurement Program (FB4P). The term ‘biobased product,' as defined by FSRIA, means a product determined by the U.S. Secretary of Agriculture to be a commercial or industrial product (other than food or feed) that is composed in whole or in significant part of biological products or renewable domestic agricultural materials (including plant, animal and marine materials) or forestry materials.

Over 120 types of products have been identified as priority items for inclusion in the FB4P program. The list includes biobased carpets, adhesive additives and adhesive mastic removers. The biobased content of listed products must be verified by testing at the University of Iowa. The FB4P website currently does not list any products as being approved under this program, though many believe this initiative will significantly influence government purchasing trends over the next 10 years.

PINE-BASED MATERIALS FOR ADHESIVES

Of the world's 3.75 billion acres of forests, only 4% carry some type of certification. The greatest threat to forest preservation in North America is urban sprawl and, in developing countries, it is illegal logging. In North America and Europe, the forest-products industry subscribes to sustainable forestry practices, and encourages its suppliers to employ these practices in their forests.

Arizona Chemical supplies several common adhesive raw materials that are sourced from sustainable forests in North America and Europe. These include the following.

Rosin Acids and Derivatives

Rosin acids are naturally occurring compounds in pine trees. Rosin helps the tree fight disease and prevent insect attack. Several types of rosin compounds are used as adhesive tackifiers, including versatile rosin ester.

Terpene Resins

Terpentine is a natural solvent used to transport rosin within the tree. Both types of compounds - rosins and terpenes - are collected, purified, and used for a variety of adhesive resins. Alpha and beta pinene resins have many adhesive uses, including pressure-sensitive tapes, labels, and hot melts.

CONCLUSION

The modern environmental movement got its start with Earth Day in 1970. Several laws and non-governmental programs have evolved to have a profound impact on the chemical industry. Today, the principles of green chemistry and Responsible Care are having an influence on the design of processes, synthesis of polymers, and formulation of adhesives. Products like rosin and terpene resins can be used in adhesive as alternatives to depleting materials, like petroleum resins. Top environmental concerns will continue to drive product development and marketing in the chemicals and adhesives industries. Demand for hot-melt adhesives continues to grow in response to stricter limits on air pollutants and volatile organic compounds. The construction industry seeks solutions that will help reduce the environmental impact of buildings. This initiative is applied to adhesives made with very low volatiles and recycled and renewable raw materials. Green chemistry, Responsible Care, regulations and non-government programs will continue to have a significant influence on the formulation, manufacture, and marketing of chemicals, adhesives, and related raw materials.

ACKNOWLEDGEMENTS

Sincere thanks to Carolyn Hart and Jill Carney for their help in conducting the research for this paper.

For more information on pine chemicals, visit the Pine Chemicals Association Inc.'s website at http://www.pinechemicals.org. For more information on Arizona Chemical, visit http://www.arizonachemical.com or e-mail azcadhesives@ipaper.com.

Sidebar: Arizona Chemical Celebrates 75th Anniversary

In 2005, Arizona Chemical celebrated its 75th anniversary with a series of special events to recognize the invaluable contributions of its team members.

"The success of Arizona Chemical over the past 75 years would not have been possible without the commitment and dedication of our outstanding team members," said Gerald Marterer, vice president of Arizona Chemical. "Whether our employees have been working for Arizona Chemical for one year or for 40 years, they have each played an important part in the company's success."

The company was originally formed in 1930 as a joint venture between International Paper and American Cyanamid to mine salt cake in Camp Verde, AZ. After the mine was closed in 1936, the company began processing tall oil and turpentine, which are co-products of the papermaking process. Arizona Chemical eventually opened plants in Panama City, FL, and Springhill, LA, beginning the company's aggressive global growth strategy that led to the successful operation of 12 manufacturing locations throughout the United States and Europe.

Today, Arizona Chemical products, including fatty acids, rosins and terpenes, are used to make fragrances, adhesives, household cleaners, soaps, inks, paints, rubber products, hydraulic fluids, roofing material, and more. The company, headquartered in Jacksonville, FL, employs more than 1,600 people worldwide.

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