CO2 Footprint Of Natural Fibres In Bio-Composite Materials

Natural fibres are becoming more and more important in our everyday lives and are experiencing an impressive renaissance as insulating materials and bio-composites in the automotive sector. In view of the social and economic challenges of the 21st century, it is important to analyse their environmental impact and ultimately ensure the sustainability of this revival. In fact, over the last twenty years, more and more natural fibres have been used in composites, especially in the automotive sector and more generally as insulating materials in other sectors.

Bio-composites consist of a polymer and natural fibres, the latter of which guarantee stability. Bio-composites with natural fibres can have similar functionality to other composites and are comparable to many end products.

The trend has been emerging for years: In 2012, 30,000 tonnes of natural fibres were used in the European automotive industry, mainly in moulded parts, an increase of around 19,000 tonnes of natural fibres in 2005. Current analyses from 2019 also clearly confirm this trend. When using such materials, it is important not only to consider their service life but also to compare it with the CO2 footprint.

The natural fibres normally used are hemp, flax, jute and kenaf. Results from 2015 show that the CO2 footprint of all four fibres is significantly lower than that of conventional glass and mineral fibres. Besides, researchers at the Nova Institute in Hürth have found that the CO2 footprints of the various natural fibres are very similar.

Initially Outstanding Comparative Values For Natural Fibres

The values are indeed impressively positive: the production of one tonne of glass fibres means a CO2 footprint of about 1.7 to 2.2 tonnes of CO2, while natural fibres only have a CO2 footprint of about 0.5 to 0.7 tonnes of CO2 per tonne of natural fibre (excluding transport to the customer). This is only one-third of the CO2 footprint of glass fibres. Even if the initial advantage in further processing decreases, natural fibre composites have a 20 to 50 per cent lower footprint compared to glass fibre composites.

When transporting the various natural fibres, carbon dioxide emissions to the factory gate of a European nonwoven manufacturer in the automotive or insulation sector amount to around 750 kg CO2 per tonne of natural fibre for all four natural fibres. Due to manual processing, jute and kenaf have lower emissions during cultivation, harvesting and decontamination, but long transport to Europe compensates for this advantage.

Is The CO2 Footprint The Right Measure?

Although the CO2 footprint is in itself a very useful tool for assessing the climate impact of products, a comprehensive ecological assessment needs to consider other environmental categories, according to Nova Institute researchers. Only the consideration of greenhouse gas emissions can lead to insufficient product testing and recommendations for action, especially if other environmental impacts have not been considered at all. One task of further studies is therefore to consider other impact categories. Sustainability also includes social and economic aspects. Since natural fibres are used in many industries, certification is a suitable instrument for demonstrating sustainability.

Antimony Oxide As Flame Retardant – Efficient But Also Dangerous?

Flame-retardant coated fabrics typically contain flame retardants in the coating. The following applies: The thinner the fabric and the coating, the more efficient flame retardant finishes are required. Antimony oxide is a so-called synergist which, in combination with halogen-containing flame retardants in plastics, is a very efficient flame retardant. Specks of dust of antimony oxide that can enter the body via the lungs are generally classified as carcinogenic.

Therefore, investigations are currently being carried out to determine whether coated textiles equipped with antimony oxide can pose a health hazard, reports Sebastian Eibl of the ‘Wehrwissenschaftliches Institut für Werk- und Betriebsstoffe’ in Erding.

The special aspect here is the fact that a harmful effect on health is not known by an absorption through the skin. This raises the question of whether a health hazard from antimony oxide is possible at all if it is present as a flame retardant embedded in the material of the coating and is not permanently released.

In order to take into account the influence of moisture and the ageing state of the tissues, ageing tests were carried out which lasted up to twelve weeks. It turned out that antimony oxide is exposed on the surface by ageing in humid air at simultaneously increased temperatures.

To predict the release behaviour over longer periods of time at room temperature from laboratory data, a ‘Arrhenius’ method was used (quantitative temperature dependence in physical and above all chemical processes in which activation energy has to be overcome at the molecular level). Here it can be concluded that the influence of humidity is critical with regard to antimony oxide exposure under typical environmental conditions - ten per cent of the total antimony oxide contained escapes at 20°C after a few years.

Health hazard – Yes Or No?

For the assessment of a possible health hazard from antimony oxide, specks of dust that enter the lungs when inhaled are particularly relevant. However, the investigations presented here only examine the basic possibility of superficial exposure. Explicit investigations on the release of dust were not carried out. As long as the material is embedded in the polymer, no relevant exposure of a user can be assumed.

However, it is not sufficient to evaluate the tissue only in its new condition. A possible exposure or release of antimony oxide must also be excluded during use. In the sense of a risk-benefit assessment, the use of antimony oxide as a flame retardant synergist can be quite sensible in the case of a justified need for efficient flame retardancy in fabrics with thin coatings.

At present, further efforts are being made to evaluate and classify the health-endangering potential. A possible regulation by "REACH" (an EU regulation) is not to be expected in an estimated period of about ten years, according to the „Bundesinstitut für Risikobewertung“ (Federal Institute for Risk Assessment).

Japanese Fire Protection Materials Made Of Paper-Thin Material

A fire sometimes seems to arise out of nowhere and can spread so quickly that the people present can hardly be rescued. This is one reason why good fire protection properties for materials used in public areas (aircraft, ships, railways, cars and public buildings such as hotels and theatres) are absolutely essential. Weserland offers halogen-free and low-smoking flame retardant compounds for these areas, which are specially adapted to the respective requirements and applications. In addition to requirements regarding flame protection, smoke gas density and toxicity – the ’classic‘ requirements, such as good cutting edge strengthening or pole and knob integration, as well as antistatic properties can also be met.

Our development teams are happy to look beyond their own horizons and have discovered new material Gulfeng from Toray (Tokyo), which combines very good fire protection properties with very good mechanical properties.

What makes Gulfeng interesting are its mechanical properties and the variety with which the fibres can be processed. Where classic materials tend to be thick and stiff, Gulfeng is thin, light and flexible. It can be woven into fabric, knitted or felted into soft mats. The material is paper-thin (0.06 mm at 60 g/sqm) and can therefore even be used in bedding. Corresponding tests were very successful and showed a good flame retardancy.

The flame-retardant effect of Gulfeng is based on the combination of two materials - polyphenylene sulphide (PPS) and oxidised polyacrylonitrite (Ox-PAN), a non-melting, temperature-resistant fibre made of thermally stabilised PAN.

Carbonization Under Exclusion Of Oxygen

When the material is exposed to a flame, all variants react in the same way: the fabric heats up and begins to melt at 285 °C. The material is then exposed to a flame. The liquid plastic then forms a thin skin around the oxidized fibres, which absorb the heat of the flame in the absence of oxygen and therefore do not burn. This leads to carbonization – the fibres are converted into resistant graphite. The molten material fills the gaps and also carbonizes, creating a closed carbon membrane that forms an excellent barrier against the flames.

Thanks to the good material properties of Gulfeng, a high level of comfort and very thin padding can be achieved. Many airlines fight for every millimetre, especially when it comes to aircraft seating.  

Another interesting development is a base material for artificial leather. Together with a Japanese artificial leather manufacturer, a light and thin material was created - and since it uses Gulfeng as the base fabric, the flame retardant is already built in. Normal artificial leather requires an additional layer as a flame blocker between the outer material and the seat upholstery. This can be omitted with the special leather or be significantly thinner, which saves weight overall and facilitates manufacture.

 

 

Functional Coating: Atmospheric Pressure Plasma Treatment On 3D Printed Polymer Surfaces

3D-printed components have an unmistakable advantage: they have a very free shape. But when it comes to coating, especially when other materials are subsequently functionalized, this free form may become a problem. The free form of the 3D components makes them inaccessible to many coating processes, especially low-pressure ones. In addition, it is difficult to combine 3D printing processes such as fused deposition modelling (FDM) with low-pressure coating processes such as sputter deposition, evaporation, plasma-assisted chemical vapour deposition.

The actual material surface is an important influencing factor that significantly determines the usability of many plastic materials. The aim is to change surface chemistry through coating and functionalisation processes. In the case of coatings, the layer-forming material brings the required chemical groups with it, while functionalization causes the chemical groups to couple directly to the surface.

The aim is to create surfaces that strengthen or reduce adhesion to other coatings or materials, reduce migration of plasticizers and improve mechanical or chemical resistance to environmental influences.

Dr Thomas Neubert, project manager at the Fraunhofer Institute for Thin Films and Surface Technology in Braunschweig, Germany, writes in an article in the journal 'Plastverarbeiter' that one solution could be to use the atmospheric pressure plasma process, which can be integrated into FDM systems in the form of plasma jets.

Combination Of 3D Printing And Plasma Jet Coating

At the Fraunhofer Institute, so-called dielectrically impeded discharges (DBE) are used. High voltages lead to an electrical gas-discharge in a gap between two electrodes, which serves as the actual energy source. It has been shown that the combination of 3D printing and plasma jet coating also successfully coats the inner surfaces of the polymer implants. Depending on the structure density, the working gas flow and the precursor vapour pressure, the coatings penetrated several millimetres into the polymer structure. It is also possible to pulse the electrical power of the plasma jet, thereby possibly increasing the density of the nucleophilic groups on the substrate surface.

The concentration on such a process becomes clear when one considers that atmospheric pressure plasma processes - compared to other gas-phase coating processes - are characterized by low investment costs, high treatment speeds and good scalability. In addition, there are various industrially established treatment sources for flat, curved or three-dimensional substrates.

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