As crude oil price volatility increases, fuel economy has become a global priority leading automakers to intensify their efforts to lightweight car parts for improved mileage. Pricing of bio-based chemicals and plastics has been less volatile than petroleum-based products. And in the longer term, they are expected to become cheaper as the technologies mature and production achieves economies of scale.
Bio composites contribute to the automotive manufacturer’s final goal by delivering a 30% weight reduction and a cost reduction of 20%. Automotive is one of market driving toward greater use of high-performance bio-based materials to meet sustainability challenges. Hence use of plant based chemicals in automotive applications has been steadily growing as per ICIS.
Natural fiber-reinforced plastics, vegetable oil-based polyols and polyamides, bio-based polyesters and thermoplastic elastomers are some of the bio-based materials being incorporated in several vehicles. A DEFRA report from 2002 projected the growth rates for bio-fibers in automotive components at 54% pa. European automakers have, in the last decade, welcomed bio-fiber reinforced polymer composites for door panels, seat backs, package trays, dashboards, and trunk liners. In recent years, North America is widely accepting bio-fiber composites where almost 1.5 million vehicles include applications for bio-fibers such as kenaf, jute, flax, hemp and sisal in combination with thermoplastic polymers such as polypropylene and polyester.
As per Dale Brosius in compositesworld.com, natural fiber provides some benefits such as lower weight, ease of recycling, carbon dioxide neutrality while burning, lower energy consumption in manufacture of natural fiber. Natural fibers can broadly be divided into three classes. They are bast fiber consisting of flax, hemp, jute and kenaf, leaf fiber consisting of sisal, henequen, pineapple and banana, seed fruit fiber consisting of cotton, kapok and coir from coconut husk.
Bast fiber has the largest potential for polymer composite. Flax and jute were the principal fibers used in biocomposites, but have been joined by higher strength industrial hemp and kenaf in automotive applications. Flax fiber called textile flax is the source for natural fiber composite. Jute is also popular in automotive industry. Kenaf fiber has been developed for natural fiber composite in the last decade. Bast fiber composites are predominantly used in automotive interior panels, such as doors, pillar trim, trunk liners and package or rear-parcel trays. Early composites, replacing wood fiberboard, were a mixture of flax and sisal fibers in an epoxy matrix, first used on the Mercedes E-Class door panels in the early 1990s.
The fibers are generally supplied in a needle-punched nonwoven mat format. The production method involves placing the mat into the heated mold, pouring liquid resin on top, and pressing until cured. Most thermosetting resins, including polyester, epoxy, phenolic and urethanes, can serve as the matrix for natural fiber composites. Such low-viscosity resins provide excellent fiber wetting and adhesion, and the composites can be compression molded in more complex shapes compared to wood fiber-based materials.
An alternate method of combining the materials is pre impregnation of the mat prior to compression molding. A technology named NafPur Tec has been used in the production of door panels for the Mercedes E- and S-Class since the late 1990s, using Baypreg F sprayable PU supplied by Bayer MaterialScience. The nonwoven flax/sisal fiber mats are sprayed on each side, and then stacked in a charge pattern before putting in the mold. The prepreg has a room temperature life of 30 to 45 minutes with molding occurring around 130°C in as little as 60 seconds per cycle.
As per ICIS, soybean-based foam, made from soybean polyols, combined with petroleum-based isocyanate, is being used in the seat cushions and backs of 2010 Ford and Lincoln car models. Ford notes that more than 2 mln vehicles in its fleet already use the bio-based foam, which reduces petroleum oil use by a total of 1.5 mln lb (680 tons). The automaker plans to convert 100% of its fleet to the biofoam. US companies manufacturing soy polyols include Dow Chemical, Cargill, BioBased Technologies and Urethane Soy Systems. Technical developments by producers have continued to improve the property profile of the polyols, and allowed their use in a broadening array of applications.
Soy- and corn-based polyols are also being used to make coatings, adhesives, sealants and elastomers. Corn-based polyols can also be used to make a more durable, scratch-resistant automotive coating. Castor oil is used as an additive for leather-like seat covers and bio-based nylon that finds applications in heat sensitive areas, such as engine compartments, or chemical sensitive areas, such as fuel lines.
In April, DSM introduced a castor oil-based polyamide engineering plastic for automotive application under the name EcoPaXX. The polyamide contains 70% castor oil-based materials, and is the first high-heat-resistant engineering plastic which has more than 50% bio-based origin but the same performance profile as its traditional counterpart. Automotive applications are mostly in the engine compartment, and commercial sales are expected in Q1-2011. DSM also launched its Palapreg ECO composite resin, which contains 55% renewable-based resources for use in exterior auto panels.
DuPont’s Sorona is currently used in fiber materials for the ceiling surface skin, sun visor and pillar garnish of Toyota’s new Sai model. The biopolymer is a polytrimethylene terephthalate resin, made from a copolymerization of terephthalic acid and DuPont’s corn-based 1,3 propanediol. Toyota’s 2009 Camry vehicles also adopted DuPont’s Zytel RS bio-based nylon for its radiator end-tank, co-developed by Japanese company DENSO. About 40% of the resin contains castor oil-based materials.
In 2009, Mazda Motor began leasing its Mazda Premacy Hydrogen RE Hybrid vehicle, in which the car seat fabric contains a high-heat-resistant polylactic acid (PLA)-based plastic called BIOFRONT made by Japanese chemical company Teijin. BIOFRONT not only overcame conventional bioplastics’ problems with hydrolytic degradation in high heat and humidity, it also boasts excellent moldability, resulting in a material that is as durable as polyethylene terephthalate (PET) but without any loss of heat resistance. When used as a compound with other petroleum-based plastics, it can also produce a very high bio-content ratio compared with other bioplastics.
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