Engineers Give Bioplastics Thumbs UpEngineers Give Bioplastics Thumbs Up
May 5, 2011
More than six in 10 American design engineers say they willconsider use of plastics made from renewable resources in the next five years.
That's a huge shift from current practice: less than 10 percentof design engineers currently use plastics made from plants or algae.
Those data points are just afew of the results from a Design News survey addressing the use of bioplastics, whichare increasingly competing directly with plastics made from oil and naturalgas, particularly for packaging and disposable products.
Somewhat surprisingly, the biggest attraction of these materials to design engineers is not environmental. It's the desire to reduce American dependenceon imported petroleum.
"I think that (bioplastics) isthe future," says Charlie Putland, a senior mechanical engineer for a companythat designs machine tool enclosures. "Petroleum supplies will eventually bedepleted and will continue to climb in price for as long as it is stillavailable. Add to that more stringent environmentalregulations (RoHS et al); bioplastics are ever-more important."
The second biggest attraction of bioplastics is an environmentalaspect - but not the one typically pitched by producers of the materials.
Four in 10 respondents to the survey said they will usebioplastics because they reduce greenhouse gases. As plants grow, theysequester carbon dioxide, which is later released when the plastics areincinerated or decompose. ?Asa result, they are said to have a neutral effect from a climate changeperspective.
CLICK HEREFOR FULL SURVEY RESULTS
Oil-based plastics, on the other hand, only release carbondioxide. Their carbon dioxidesequestration phase took place in primordial times.
For every 100 kg of polypropylene or polyethylene manufacturedusing "biocarbon" (such as starch or polylactic acid) as opposed to fossilfuel-based carbon, 320 kg of carbon dioxideemissions reduction are achieved in an "intrinsic" analysis, according toRamani Narayan, a professor of material science and chemical engineering atMichigan State University.
In an intrinsic analysis (spelled out in ASTM D6866), thereduction achieved is equal to the amount of biocarbon content in thebioplastic.
Some design engineers, however, say that it's still notclear what impact bioplastics have on climate change.
"Renewables work only if performance is comparable and the'cradle-to- grave' environmental impact is less than more conventionalmaterials," says David Hutchison, a manager of mechanical engineering for amanufacturer of camping equipment. "Isee too narrow a vision used when assessing the impact of alternate materialslike the increased use of non-renewables to produce renewables."
He raises the point that the oil used to grow and harvest cropsand then transport them to processing locations may outweigh any benefitderived from the carbon dioxide sequestration when the plant is growing. ?A similardebate has surrounded biofuels such as ethanol.
Narayan and others worked todevelop American and global standards that measure the "cradle-to-factory-gate"environmental footprint of bioplastics. That data can now be determined in ASTMD7075.
Some environmental advocateseven go farther to demand a "cradle-to-cradle" footprint to determine the totalimpact of a material from its origins to its end-of-life or re-use. In thatview, the best materials are those that can be "upcycled" following their useto a more demanding application. One example could be the use of PET sodabottles in composites for car parts. Design programs that subscribe to the"cradle-to-cradle" approach put a high value on recyclability, notbiodegradability.
Engineers Give Bioplastics Thumbs Up_A
The third biggest benefit of designs that incorporate bioplasticsis not a surprise - it's a good marketing story. That'sclear from the plethora of advertisements touting green virtues in the past 12months. Some examples:
Stonyfield Farms replaced oil-based polystyrene in its multipack yogurt cupswith polylactic acid (PLA), which is a plastic made from corn and syntheticadditives.
Citing "its heritage as an innovator and leader in environmentalsustainability," PepsiCo announced development of the world's first PET plasticbottle made from switch grass, pine bark and corn husks. In the future, thecompany expects to broaden the renewable sources to include orange peels,potato peels, oat hulls and other agricultural by-products from its foodsbusiness.
Papermate introduced a pen last year with components that will biodegrade inabout a year when buried in soil or placed in an industrial compost facility.The biodegradable components are molded with Mirel, a biodegradable corn-basedbioplastic called upolyhydroxyalkanoate (PHA).
The biodegradability aspect is an area that's declining inimportance overall and is of less interest to design engineers, who aregenerally looking for products with good durability.
Some marketers overplayed the biodegradability card with commentsthat were sometimes misleading or even outright incorrect. For example, somemade claims that their bioplastics would degrade in landfills, but landfillsare generally oxygen- and moisture-free to prevent any biodegradation, whichcould cause toxic chemicals to leak into aquifers.
Many of the newer bioplastics are not biodegradable atall.
DuPont, for example, is one ofthe leaders in developing engineering polymers that have bioplasticroots. At K 2010 held in Dusseldorf, Germany last year, DuPont's standdisplayed 10 products made at least in part from bioplastics.
DuPont worked with Takata-Petri of Aschaffenburg, Germany todevelop the industry's first renewably sourced thermoplastic elastomer for usein airbag systems. The material contains a minimum of 35-percent renewablecontent by weight derived from non-food biomass. The newly developed grade ofHytrel is based on a thermoplastic ether-ester elastomer (TPC-ET) with hardsegments of polybutylene terephthalate and soft segments that contain apolyether derived from non-food biomass.
DuPont stands alone among the major chemical companies as asignificant investor in multiple bioplastic technologies. Most renewablysourced materials are being developed by start-ups and technology spin-offs.
"DuPont's strategy is to offer polymers that are at least 20percent renewably sourced and have equal or better performance than theentirely petrochemically based materials they replace," says Marsha A. Craig, DuPont's global businessmanager for renewably sourced materials.
The company's portfolio keepsexpanding and now includes Sorona EP thermoplastic polymers, which exhibitmolding characteristics similar to high-performance PBT (polybutyleneterephthalate); Hytrel RS thermoplastic elastomers, which contain 35 to 65percent renewably sourced material and provide the same established performancecharacteristics of original Hytrel; and a family of Zytel RS long chain nylons.
Engineers Give Bioplastics Thumbs Up_B
One in three designengineers surveyed say they plan to use bioplastics because of their superiorproperties.
"(Bioplastics) will only be a good choice if they perform equallyor better than their petroleum-based cousins," says Roger Sharp, a toolengineer. "We shouldn't be using them simply because they claim to be green."
Most bioplastics have inferiormechanical properties compared to oil-based plastics, particularly in thermalresistance. A few, however, have superior, or even unique, property profiles. The engineering properties ofrenewably sourced plastics vary widely because of the wide range of biologicalmaterials they are made from.
One interesting example is aclass of polyamides made from castor beans.
In 1942, BASF chemists in Germany invented castor-derivedpolyamide 11 and 12, which have different properties from their better-knownpolyamide cousins, polyamide 6 and 66. Polyamide 11, sold as Rilsan 11, byArkema, offers excellent chemical resistance, as well as impact strength, highservice temperatures and dimensional stability. It's widely used for oilcountry umbilical cables, automotive fuel and fluid transfer tubing, and transfusion bags.
Since the "renewable" aspect became a selling point, four othercompanies announced development of their own castor-derived polyamides: DuPont,Rhodia, BASF and Evonik. BASF had lost rights to the material.
In another example, DuPont says its Sorona plastic has improvedsurface appearance and lower warpage compared to the PBT-type polyesters ittargets.
The extent to which design engineers will make greateruse of bioplastics will depend on a variety of factors, led by cost andproperty deficiencies for the most common grades.
In cases where there are clearchoices between petrochemically based plastics and those derived from renewableresources, there generally is a premium for the latter. And sometimes thepremium is significant.
One example is a class of bioplastics calledpolyhydroxoxyalkanoate (PHA). The leading developer is Telles, a joint ventureof Archer Daniels Midland and Metabolix. Its product, trade named Mirel, ismade from corn sugar via a fermentation process at an Iowa biorefinery. Itsprice is about 2.5 times higher than ABS, an entry-grade thermoplastic. Thepitch is that it has a better carbon footprint than ABS and is biodegradable.
That type of argument isn't flying with many of the designengineers surveyed.
"Bioplastics are great if they're competitive on cost andproperties," says one design engineer. "Otherwise they're a waste of money."
Several respondents to thesurvey also made comments on the potential impact on food supplies if bioplastics are widely used.
CLICK HEREFOR FULL SURVEY RESULTS
"Ethically, I cannot in good conscience recommend the use ofplastics made from food crops," says David E. Palmer, a metallurgist in the Powertrain Div. of Bombardier Recreational Products. "I am also skeptical about the purported environmentalbenefits. It is really very dishonest to pretend that carbon dioxide emissionscreated in generating the energy needed to convert these crops into plastics issomehow offset by the carbon dioxide absorbed by the crops - wouldn't thatacreage be planted anyway? That being said, I would potentially be interestedin plastics made from biologically based materials - if they were made fromwaste materials, for example."
Palmer's comments reflect a growing consensus among thepublic in general. The firstmajor bioplastics' projects in the U.S. focused on the use of corn. Most newprojects target use of plants not used for food or waste.
For example, Ford Motor, a leader in the use of naturalmaterials, is studying use of Indian grass that grows wild in Michigan andelsewhere in the Midwest.
"The big motivation in working on natural fiber is a 30-percentweight reduction compared to glass fiber," says Dr. Deborah Mielewski, theleader of a Ford engineering team studying sustainable materials. "Also, glassfiber takes a lot of energy to produce, and you also get the carbon dioxidereduction because you're sequestering carbon dioxide in the plant when you growit."
Cereplast is developing polymercompounds made from algae.
Over time, the developers ofplastics made from annually renewable resources will solve many of theobjections they currently face. They will be made from resources that don'tthreaten global food supplies. Their properties will improve. They will becomemore cost competitive as the price of oil rises. Governments will enact morelaws that address global warming.
Given those factors, the role of bioplastics likely will remainsmall.
For example, a study conductedby BCC Research forecasts that bioplastics will grow at a 41 percent annualrate through 2015 to reach 3.2 million metric tons, but they will still onlyaccount for about 1 percent of theglobal plastics market.
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