Tag Archives: multi-walled carbon nanotubes (MWCNTs)

Plantains and carbon nanotubes to improve cars

I always enjoy the unexpected in a story and this one has to do with plantains and luxury cars, from a July 29, 2020 news item on phys.org (Note: A link has been removed),

A luxury automobile is not really a place to look for something like sisal, hemp, or wood. Yet automakers have been using natural fibers for decades. Some high-end sedans and coupes use these in composite materials for interior door panels, for engine, interior and noise insulation, and internal engine covers, among other uses.

Unlike steel or aluminum, natural fiber composites do not rust or corrode. They can also be durable and easily molded. The biggest advantages of fiber reinforced polymer composites for cars are light weight, good crash properties, and noise- and vibration-reducing characteristics. But making more parts of a vehicle from renewable sources is a challenge. Natural fiber polymer composites can crack, break and bend. The reasons include low tensile, flexural and impact strength in the composite material.

Researchers from the University of Johannesburg [South Africe] have now demonstrated that plantain, a starchy type of banana, is a promising source for an emerging type of composite material for the automotive industry. The natural plantain fibers are combined with carbon nanotubes and epoxy resin to form a natural fiber-reinforced polymer hybrid nanocomposite material. Plantain is a year-round staple food crop in tropical regions of Africa, Asia and South America. Many types of plantain are eaten cooked.

A July 29, 2020 University of Johannesburg press release, which originated the news item, delves into plantains and how their fibers enhance nanocomposites destined for integration into luxury cars,

Plantain is a year-round staple food crop in tropical regions of Africa, Asia and South America. Many types of plantain are eaten cooked.

The researchers moulded a composite material from epoxy resin, treated plantain fibers and carbon nanotubes. The optimum amount of nanotubes was 1% by weight of the plantain-epoxy resin combined.

The resulting plantain nanocomposite was much stronger and stiffer than epoxy resin on its own.

The composite had 31% more tensile and 34% more flexural strength than the epoxy resin alone. The nanocomposite also had 52% higher tensile modulus and 29% higher flexural modulus than the epoxy resin alone.

“The hybridization of plantain with multi-walled carbon nanotubes increases the mechanical and thermal strength of the composite. These increases make the hybrid composite a competitive and alternative material for certain car parts,” says Prof Tien-Chien Jen.

Prof Jen is the lead researcher in the study and the Head of the Department of Mechanical Engineering Science at the University of Johannesburg.

Natural fibres vs metals

Producing car parts from renewable sources have several benefits, says Dr Patrick Ehi Imoisili. Dr Imoisili is a postdoctoral researcher in the Department of Mechanical Engineering Science at the University of Johannesburg.

“There is a trend of using natural fibre in vehicles. The reason is that natural fibres composites are renewable, low cost and low density. They have high specific strength and stiffness. The manufacturing processes are relatively safe,” says Imoisili.

“Using car parts made from these composites, can reduce the mass of a vehicle. That can result in better fuel-efficiency and safety. These components will not rust or corrode like metals. Also, they can be stiff, durable and easily molded,” he adds.

However, some natural fibre reinforced polymer composites currently have disadvantages such as water absorption, low impact strength and low heat resistance. Car owners can notice effects such as cracking, bending or warping of a car part, says Imoisili.

Standardised tests

The researchers subjected the plantain nanocomposite to a series of standardised industrial tests. These included ASTM Test Methods D638 and D790; impact testing according to the ASTM A-370 standard; and ASTM D-2240.

The tests showed that a composite with 1% nanotubes had the best strength and stiffness, compared to epoxy resin alone.

The plantain nanocomposite also showed marked improvement in micro hardness, impact strength and thermal conductivity compared to epoxy resin alone.

Moulding a nanocomposite from natural fibres

The researchers compression-moulded a ‘stress test object’. They used 1 part inedible plantain fibres, 4 parts epoxy resin and multi-walled carbon nanotubes. The epoxy resin and nanotubes came from commercial suppliers. The epoxy was similar to resins that auto manufacturers use in certain car parts.

The plantain fibres came from the ‘trunks’ or pseudo-stems, of plantain plants in the south-western region of Nigeria. The pseudo-stems consist of tightly-overlapping leaves.

The researchers treated the plantain fibers with several processes. The first process is an ancient method to separate plant fibres from stems, called water-retting.

In the second process, the fibres were soaked in a 3% caustic soda solution for 4 hours. After drying, the fibres were treated with high-frequency microwave radiation of 2.45GHz at 550W for 2 minutes.

The caustic soda and microwave treatments improved the bonding between the plantain fibers and the epoxy resin in the nanocomposite.

Next, the researchers dispersed the nanotubes in ethanol to prevent ‘bunching’ of the tubes in the composite. After that, the plantain fibres, nanotubes and epoxy resin were combined inside a mold. The mold was then compressed with a load for 24 hours at room temperature.

Food crop vs industrial raw material

Plantain is grown in tropical regions worldwide. This includes Mexico, Florida and Texas in North America; Brazil, Honduras, Guatemala in South and Central America; India, China, and Southeast Asia.

In West and Central Africa, farmers grow plantain in Cameroon, Ghana, Uganda, Rwanda, Nigeria, Cote d’Ivoire and Benin.

Using biomass from major staple food crops can create problems in food security for people with low incomes. In addition, the automobile industry will need access to reliable sources of natural fibres to increase use of natural fibre composites.

In the case of plantains, potential tensions between food security and industrial uses for composite materials are low. This is because plantain farmers discard the pseudo-stems as agro-waste after harvest.

Here’s a link to and a citation for the paper,

Physical, mechanical and thermal properties of high frequency microwave treated plantain (Musa Paradisiaca) fibre/MWCNT hybrid epoxy nanocomposites by Patrick Ehi Imoisili, Kingsley Ukoba, Tien-Chien Jen. Journal of Materials Research and Technology Volume 9, Issue 3, May–June 2020, Pages 4933-4939 DOI: https://doi.org/10.1016/j.jmrt.2020.03.012

This paper is open access.

Nanoparticles make home refrigeration more accessible

Periodically, academic institutions recycle news about their research. I think it happens when, for one reason or another, a piece of news (somebody was exciting) slips past with little notice. I’m glad this June 1, 2020 news item on phys.org brought this research from South Africa to my attention,

Power consumption of a home refrigerator can be cut by 29% while improving cooling capacity. Researchers replaced widely used but environmentally unfriendly R134a refrigerant with the more energy-efficient R600a dosed with multi-walled carbon nanotube nanoparticles (MWCNT). This drop-in refrigerant replacement can be deployed in the field by trained technicians, says an engineer from the University of Johannesburg.

A May 30, 2020 University of Johannesburg press release on EurekAlert, which originated the news item, provides more details about the research,

This test of nanoparticle-dosed refrigerants is a first of its kind and recently published in Energy Reports, an open-access journal. The results can help make home refrigeration more accessible for low-income families.

R134a is one of the most widely-used refrigerants in domestic and industrial refrigerators. It is safe for many applications because it is not flammable. However, it has high global warming potential, contributing to climate change. It also causes fridges, freezers and air-conditioning equipment to consume a lot of electrical energy. The energy consumption contributes even more to climate change.

Meanwhile, a more energy-efficient refrigerant can result in much lower electricity bills. For vulnerable households, energy security can be improved as a result. Improved energy economy and demand-side management can also benefit planners at power utilities, as cooling accounts for about 40% of energy demand.

Nanoparticles enhance power reduction

Nano eco-friendly refrigerants have been made with water and ethylene glycol. Previous studies showed reduced energy use in nano-refrigeration, where refrigerants were dosed with multi-walled carbon nanotube (MWCNT) nanoparticles. The nanoparticles also resulted in reduced friction and wear on appliance vapour compressors.

But previous research did not test the effects of MWCNT’s on hydro-carbon refrigerants such as R600a.

In a recent study, researchers at the University of Johannesburg tested the drop-in replacement of environmentally-unfriendly refrigerant R134a, in a home refrigerator manufactured to work with 100g R134a.

They replaced R134a with the more energy-efficient refrigerant R600a, dosed with MWCNT nanoparticles.

Reduces electricity use by more than a quarter

The researchers removed the R134a refrigerant and its compressor oil from a household fridge. They used a new refrigerant, R600a, and dosed it with multi-walled carbon nanotubes (MWCNTs). Mineral oil was used as a lubricant. The new mix was fed into the fridge and performance tests were conducted.

They found that the R600a-MWCNT refrigerant resulted in much better performance and cooling capacity for the fridge.

“The fridge cooled faster and had a much lower evaporation temperature of -11 degrees Celsius after 150 minutes. This was lower than the -8 degrees Celsius for R134a. It also exceeded the ISO 8187 standard, which requires -3 degrees Celsius at 180 minutes,” says Dr Daniel Madyira.

Dr Madyira is from the Department of Mechanical Engineering Science at the University of Johannesburg.

“Electricity usage decreased by 29% compared to using R134a. This is a significant energy efficiency gain for refrigerator users, especially for low income earners,” he adds.

To gain these advantages, the choice of MWCNT nanoparticles is critical, he says.

“The MWCNT’s need to have nanometer-scale particle size, which is extremely small. The particles also need to reduce friction and wear, prevent corrosion and clogging, and exhibit very good thermal conductivity,” says Dr Madyira.

Managing flammability

The new refrigerant mix introduces a potential risk though. Unlike R134a, R600a is flammable. On the other hand, it is more energy efficient, and it has a low Global Warming potential. Some refrigerator manufacturers have already adopted production with R600a and these appliances are available in the market.

“To do a safe drop-in replacement, no more than 150g of R600a should be used in a domestic fridge,” says Dr Madyira. “Before the replacement, the fridge used 100g of R134a gas. We replaced that with 50g to 70g of R600a, to stay within safety parameters.”

An untrained person should not attempt this drop-in replacement, says Dr Madyira. Rather, a trained refrigeration technician or technologist should do it.

Replacement procedure

“Mineral oil is used as the compressor oil. This should be mixed with the recommended concentration. A magnetic stirrer and ultrasonicator are needed to agitate and homogenize the ingredients in the mixture. The mixture can then be introduced into the compressor. After that, R600a can be charged into the refrigerator compressor, while taking care to not use more than 150g of the gas,” says Dr Madyira.

A woman’s fridge is her castle [Haven’t seen that kind of reference in many years]

A far more energy-efficient refrigerant, such as the R600a-MWCNT mix, can save consumers a lot of money. Vulnerable households in hot climates in developing countries can benefit even more.

Low income earners in many countries are dependent on home fridges and freezers to safely store bulk food supplies. This greatly reduces the risk of wasting food due to spoilage, or food poisoning due to improperly stored food. These appliances are no longer a luxury but a necessity, says Dr Madyira.

Without fridges, people may be forced to buy food daily in small quantities and at much higher prices. Because daily buying may not be required anymore, travel time and costs for buying food can be much lower as well.

Refrigeration also makes it possible to safely store more diverse food supplies, such as fresh fruit and vegetables. Medicines that require cooling can be stored at home. This can make more balanced diets and nutrition, and better physical health, more accessible for a low-income household.

Grid power still rules for low-income refrigeration

From a sustainability point of view, it can look preferable to run most home fridges and freezers from solar power.

However solar panels, backup batteries, and direct current (DC) fridges are still too expensive for most low-income families in areas served by power utilities.

Energy-efficient, alternating current (AC) fridges running on grid power may be more affordable for most. Further cutting power consumption with R600a-MWCNT refrigerant can bring down costs even more.

Refrigeration for all vs demand-side management

As more low-income households and small businesses switch on grid-powered fridges, freezers and air-conditioning, power demand needs be managed better

In South Africa where the study was conducted, the state-operated power utility faces huge challenges in meeting demand consistently. Long-lasting rolling blackouts, known as load-shedding, have been implemented as a demand-side power management measure.

Shaving off more than a quarter of the power consumption of fridges, freezers and air-conditioning units can free up national power supply for improved energy security.

Here’s a link to and a citation for the paper,

Energy performance evaluation of R600a/MWCNT-nanolubricant as a drop-in replacement for R134a in household refrigerator system by T.O Babarinde, S.A Akinlabi, D.M Madyira. Energy Reports Volume 6, Supplement 2 ([proceedings] The 6th International Conference on Power and Energy Systems Engineering (CPESE 2019), 20–23 September 2019, Okinawa, Japan), February 2020, Pages 639-647 DOI: https://doi.org/10.101/j.egyr.2019.11.132

This paper is open access.