Kenaf—Natural Fiber for Lightweighting

By on March 19, 2019 in IN THE NEWS, MATERIAL MATTERS

Fast-growing, sustainable and easy on the environment

“Someday you and I will see the day when auto bodies will be grown down on the farm.” Henry Ford, 1934

That someday has yet to come—but it’s getting closer.

Ford did try his hand at a “plastic car made of soybeans” in 1941. It had 14 plastic panels that the designer, Lowell E. Overly, said were made from a “… soybean fiber in a phenolic resin with formaldehyde used in the impregnation.” The car only weighed 2,000 pounds, which was a third lighter than one made of steel.

With the onset of World War II, auto production was suspended as the automotive industry turned its attention to supplying military vehicles. There was no time for experimental cars, only Jeeps, tanks and transport trucks.

Henry Ford died in 1947, and no one at his namesake company took up the green mantle. But the idea of using natural fibers has been revived as a way to reduce weight and increase fuel economy with inexpensive, environmentally friendly materials.

Toyota got on the natural-fiber reinforced composites bandwagon in 1999 when it used kenaf to strengthen a phenolic-resin door trim in the Kijang minibus manufactured in Indonesia.

And Kenaf Is?
Kenaf? That might not be familiar. Flax, hemp, jute, yes. But kenaf? They are all bast fibers, which are stiff when used to reinforce a composite. The stems of bast plants have pulp or short fibers cores with long fibers encasing them. Kenaf has a low density at around 1.2 to 1.4 g/cm³ and a high tensile strength of about 700 MPa.

The plant is grown primarily in China, India and Thailand. Malaysia sees it as a cash crop of the future and is spending millions of ringgits (its currency) on research.

Other features that make kenaf desirable include its CO2 absorption rate, the highest of any plant. Basically, it has net zero carbon emissions. It doesn’t require irrigation in floodprone areas like Bangladesh. And it self-fertilizes because kenaf leaves stay on the ground, providing nourishment for the next crop.

Kenaf takes considerably less energy to process when compared to glass fibers. To produce one pound of glass fiber takes 23,500 British thermal units (BTUs) of energy. For one pound of kenaf fiber, only 6,500 BTUs are needed.

Another positive for kenaf is as much as 40 percent of its stalks produce usable fiber That’s twice as much as jute, hemp and flax. And then there is the incredible growth rate. The plant grows from seed to heights of 3.6 meters to 4.3 meters (12 ft to 14 ft) in five to six months. Asian kenaf is predominantly grown for the fiber, and soaking the stalks during the retting process, combined with manual removal of the fibers, is believed to result in superior reinforcement quality.

Kenaf, flax, jute and hemp are seen as low-cost and low-weight alternatives to fiberglass and are part of a “green” industry with enormous potential.

Other features that make kenaf desirable include CO2 absorption rate, the highest of any plant. Basically, it has net zero carbon emissions.

In addition, these natural fibers are easy to recycle, provide thermal and acoustic insulation and have carbondioxide neutrality. That means its burned fibers give off no more carbon dioxide than they consumed growing. It’s been found that on average, producing natural-fiber composites (biocomposites—biopolymers reinforced by plant fibers) uses 60 percent less energy than what is used to manufacture glass fibers.

BMW and Kenaf
Who is using kenaf? BMW, for one. It teamed up with Dräxlmaier, a German automotive component supplier, to find sustainable lightweight design solutions using biocomposite materials.

One problem they found with natural fibers was their rough structure, making them unacceptable for interior use. The question became how could natural-fiber materials find their way into the vehicle interiors as a styling element on the one hand and save weight on the other hand.

Dr. Isabella Schmiedel, Dräxlmaier’s head of technology and innovation management of interiors, and several of her colleagues, wrote a paper, “Use of Visible Natural Fibres in Vehicle Interiors,” describing their efforts to overcome the problem for a BMW i3 electric vehicle (EV).

This is what they did. “In the BMW i3 door panelling and the instrument panel cover, a kenaf natural fibre nonwoven fabric is combined with fibres made of polypropylene (PP), which are with about 0,9 g/cm3 the lightest of all chemical fibres. In addition, a wafer-thin black PP decorative film (200 µm) is laminated onto the surface in the manufacturing process.

“The natural fibre composite material that is produced in this way also shows the advantages of material characteristics in the case of a crash: Because natural fibre-reinforced plastics (NFP) do not splinter and break without any sharp edges. Basically, one can say that NFP exhibit a high degree of rigidity and strength as well as a low density. Thus, they are mechanically very resilient and light at the same time.”

They go on to say, “Other decors are much heavier than this: The mass per unit area of a conventionally used TPO foam film (thermoplastic elastomer on an olefin basis) is four times the weight at 720 g/m². As a result, it can be seen that when using visible natural fibre surfaces, they only have to be sealed with a comparably thin film, as their structure should remain visible to passengers as a styling element. This shows that a weight reduction of about 30 to 45% can be achieved.”

The end result? “A variety of tests was made to prove suitability for daily use. Thanks to the specially developed decorative film, the BMW i3 door panelling was not only up to standard with regards to a flammability rate of 15 mm/min, even the scratch resistance is comparable with models made of conventional injection moulded plastic.

The question became how could natural-fiber materials find their way into the vehicle interiors as a styling element on the one hand and save weight on the other hand.

“Olfactory characteristics of the kenaf door panelling were also tested with the VDA 270 test standard of the German Automobile Industry Association (determination of the odour characteristics of materials in vehicle interiors) and are also up to standard.”

Mike Clowry, vice president of advanced development and engineering at the International Automotive Components Group (IAC) points out that car interiors are where manufacturers are using biocomposites.

“We have produced map boxes, trunk trim, rear seat liners and door components employing natural fiber composites,” Clowry said. In 2017, IAC produced what it said was the first natural-fiber composite sunroof frame. It was 70-percent hemp and kenaf fiber, bringing the frame in 50-percent lighter than a metal sunroof frame. It is now found on all Mercedes-Benz EClass and A-Class cars.

Sun and panoramic roofs have become more in demand for vehicles of all sizes and segments. IAC Director of Advanced Engineering Fritz Schweindl explained that “This market trend inspired IAC to develop stiff and lightweight concepts, which help realize different fixation concepts on the car body, the sun roof or the panoramic roof module. Within its strategy of viable innovation, IAC leveraged its integrated material and process know-how to provide our OEM customers with significant weight savings, a lower carbon footprint for their vehicles and a more efficient production process.”

Henry Ford’s Biocomposite Legacy
When you’re talking biocomposites, all roads lead back to Ford. And that road began years before Henry famously whacked his soybean car with an ax to show it survived without dents or dings. (There is some dispute whether he hit the actual soybean car or another with a soybean panel.) The company was using renewable materials as far back as 1915 when wheat-based glue, soybean wool and soybeans were used in the Model T.

Ford’s interest in developing the soybean car was said to have arisen out of concern for the plight of farmers during the Great Depression. He wanted to provide another market for crops by sourcing them for car parts and fuel.

Ford began to research how to integrate natural fibers into automobiles, which led to the 1941 T concept (soybean) car with a body of primarily soy resin-reinforced hemp, sisal and wheat straw composites, fueled by hemp oil.

World War II stalled further research. Interestingly, the war brought kenaf onto the research radar because jute imports from Asia came to a halt. Rope was made from jute, and rope was needed in the war effort. Kenaf could be a jute substitute.

In the 1950s, the Agricultural Research Service (ARS) of the U.S. Department of Agriculture looked at more than 500 plant species as potential fibers for pulp and paper manufacturing. Kenaf was selected as the most promising non-wood fiber plant.

Desirable Kenaf Properties
Ford was back on the kenaf track with the 1998 Ford Cougar. It sported a polypropylene plastic and kenaf-fiber composite in its interior door panels. The 2000 Mustang was slated to have kenaf in its trunk liners. A reason for choosing kenaf was its shatter-resistant properties.

The question became how could natural-fiber materials find their way into the vehicle interiors as a styling element on the one hand and save weight on the other hand.

“The natural fibers are very ductile, and they don’t splinter, so they manage energy well during side impacts,” said Ken Urolini, who was the area manager for door-trim engineering at Ford’s Visteon Automotive Systems. Urolini pointed out that natural-fiber composite components weigh about 30 percent less than traditional wood-based materials. They also cost less because they take half as long to make.

According to Liat Margolis, director of research at the Material ConneXion, a materials consultancy, fiber composites are replacing petroleum-based products, including resins in thermoset plastics. These are toxic and are not very biodegradable. On the other hand, kenaf fiber mixed with a thermal plastic like polypropylene is easier to re-melt and reuse.

“Kenaf stalks, which are comparable in strength to carbon or glass, are replacing fiberglass, and polypropylene is replacing liquid resin, which eliminates a lot of the toxic chemicals for workers,” Margolis said.

“People are fusing old materials with different physical treatments to make different materials. It’s like old-time alchemy,” said George Beylarian, founder and president of Material ConneXion.

Ford’s 2002 Escape had interior door bolsters made from kenaf in its effort to use more sustainable materials. Blended with polypropylene in a 50-50 mixture, kenaf was reported to reduce the door component’s weight by 25 percent compared with conventional materials. Other eco-friendly materials were soy-foam seats and head restraints, recycled plastic bottles in the carpeting, 10 pounds of scrap cotton from manufacturing denim jeans and recycled tires. Ford said the Escape would be 85-percent recyclable when it reached end of life.

“People are fusing old materials with different physical treatments to make different materials. It’s like oldtime alchemy.” — George Beylarian

Ford’s Biomaterials Efforts
Debbie Mielewski has been leading a team in Ford’s biomaterials department for almost two decades. The aim has been to develop strong plant-based plastics that could replace conventional ones. This research began as the environment and oil supplies became higher priority issues.

Despite that, Mielewski had a hard time getting support for her research. “We were told over and over it could not be done,” she said. “We got thrown out of every conference room in the company.” Initially, coming up with viable results proved difficult, and the team was in danger of losing funding. “But Bill Ford stepped in and kept us going,” Mielewski said. “He said simply, ‘It’s the right thing to do.’”

Then, in 2007, oil prices took a sharp upturn as world production stalled. “Oil went from $40 to $160 a barrel. And we were ready with soybean foam that met all the requirements for durability and performance,” Mielewski said. Suddenly, plants replacing oil looked like the smart way to go.

Kenaf’s Future in the Automotive Industry
What lies ahead for kenaf and other biocomposites components?

Obed Akampumuza et al, Donghua University, Shanghai, wrote in their paper, “Review of the Applications of Biocomposites in the Automotive Industry,” “Demand for a better end of life disposal and lightweight automotive parts as a gateway to easing on the automotive fuel consumption and this cutting greenhouse gas emissions will continue to spur an increasing research on the feasibility of natural fiber-based composites in automotives.

“With a flicker of hope so far manifested, car makers in the major industrial blocks; Europe, Japan, Korea, Brazil, and the United States are expected to keep up with the pursuit of these materials. The growing awareness amongst the end users, together with continued government and environmental bodies’ involvement will help achieve more innovations in the coming future.”