Materials Specifier: The search for a “green” material

An environmental consciousness is emerging faster than biopoly­mer materials are being developed.

With all the recent activity around going green, it wasn’t that surprising when a customer called materials database experts IDES (Laramie, WY) looking for a way to use biodegradable plastics in an electronics application. In addition to biodegradability, she wanted a material that would perform like ABS or PA (polyamide).
Biodegradability seemed to be the most important criteria for this application, but the first step IDES took was to determine how ABS and PA behave in terms of a few specific requirements. Using the Property Search in the IDES Prospector search engine, researchers put together a typical profile for strength, toughness, and thermal properties of ABS and PA.

Application: Electronics application.

Goal: Use biodegradable plastics.

Criteria and most important properties: Biodegradability; material must perform like ABS or PA.

IDES search notes: First, we conducted a search for “generic symbols” ABS, nylon 6, and nylon 6/6. This narrowed the possibilities down to 15,059 materials from 77,127. Next, we looked at only the unfilled versions (6843 materials). To look at typical characteristics, our team performed some iterative searches, deciding to focus on four different properties: tensile strength, flexural modulus, notched Izod, and DTUL at 66 psi. These are common properties that are both reported by suppliers and used by specifiers/designers to understand a material’s performance.

It’s important to note that we defined “typical” by saying that at least 50% of the materials fit in the bounds of the search. This is the reason an iterative search technique was used.

Here’s an example of how typical flex modulus was determined using Prospector. Without a histogram of values to view and see where most values fit, it was simplest to start by searching for everything greater than 0. Results were then sorted by flex modulus and an average of 330,000 psi was determined from the values found at the middle of the 5450 results. Using that value as the midpoint, the search was expanded from there.

By editing the search and tweaking the flexural modulus range to include materials from 280-380 ksi, about 50% of the materials were found to be in range. This value range was accepted as the “typical” flexural modulus. This iterative process was performed for other properties as well. The results:
• flexural modulus: 280,000-380,000 psi
• tensile strength: 5800-8700 MPa
• notched Izod: 1.6-4.0 ft-lb/in
• DTUL @ 66 psi: 100-300°F

Without considering biodegradability, this search resulted in 621 total materials. After searching features for “biodegradable,” though, no matching materials came back. Searching on the Agency Ratings that might relate to compostability, ASTM D 6400 and EN 13432, was the next step. Again, there were no materials that met these requirements.

While we didn’t find any materials, we were able to help the customer see that, right now, it might not be possible to find a biodegradable alternative to her current material.

Commentary by consultant Jack Avery: The current petroleum pricing volatility continues to drive programs targeted to develop renewable materials. While it has not been a rapid process, these initiatives will ultimately provide materials based on renewable raw materials that will perform like an engineering thermoplastic and be truly “green.”

However, most of the biodegradable and sustainable materials currently on the market are primarily suitable for packaging applications. PLA, PHA, starch-based materials, and some blends can be found in disposable utensils, food containers, and consumer goods packaging, but not in mobile phones, laptops, or electrical applications.

The rapid increase in plastics material pricing during the past 24 months has provided the push for OEMs to substitute non­petroleum materials in nonpackaging applications. Yet, designers have found that alternative materials do not have the performance capabilities required—i.e., heat, impact, strength, and stiffness.

As the need becomes more pronounced and the demand increases, resin companies are taking steps to meet this demand. Intermediates based on corn, castor oil, and other raw materials are being developed, which will lead to new families of sustainable materials.

Some companies, such as DuPont, are beginning with hybrid materials. These materials have building blocks based on both petroleum-based and green materials. They have the capability to provide performance required for industrial applications while also providing renewable content. Although not ideal, they provide an opportunity to move into the green arena.

While a few material suppliers are in the process of developing materials based totally on renewable sources, they have yet to be commercialized in industrial applications.

DuPont Engineering Polymers has developed a fermentation process by which it is possible to manufacture 1,2-propanedion (PDO) and/or 1,4-butanediol from corn starch. These materials, called BioPDO, are then reacted with either terephthalic acid (TPA) or dimethylterphthalate (DMT) to produce a bio-polyester alternative to polybutylene terephthalate (PBT). According to DuPont, the production of BioPDO requires 40% less energy and generates 20% less greenhouse gases than its petrochemical counterpart.

DuPont has also developed a material based on this building block, called Sorona, which has approximately a 37-40% renewable raw material content along with mechanical and processing properties similar to PBT. It is being tested as an alternative to PBT and PA6 in automotive applications. Other potential areas of application are electrical/electronic systems and industrial and consumer goods.

Hybrid resins manufactured and sold by Cereplast Inc. replace 50% or more of the petroleum content used in traditional plastic resins with bio-based materials such as starch from corn, wheat, and potatoes. Cereplast recently introduced the first member of its hybrid resin family, called Biopropylene, which is said to offer properties similar to traditional PP. This material also replaces approximately 50% of the petroleum-based content with starch.

In other developments, BASF and Arkema are developing polyamide materials (PA6/10 and PA11) using sebacic acid derived from castor oil as a raw material.

These hybrid materials, while not truly green, provide the opportunity for OEMs to use more environmentally sustainable materials and to reduce the industry’s reliance on petroleum-based raw materials.

?
Arkema | www.arkema-inc.com
Avery Consultants | www.averyconsultants.com
BASF | www.basf.com
Cereplast Inc. | www.cereplast.com
DuPont | plastics.dupont.com
IDES | www.ides.com