Waste Prevention In Composite Materials: Additives Optimise Sustainability And Efficiency

Improving recycling rates and thus improving the consumption of resources is one of the outstanding tasks in the development and production of composite materials today. To this end, waste must be reduced and production residues returned to the manufacturing process, which is an important factor in reducing costs and increasing efficiency in plastics processing.

For example, newly developed polymer stabilizers enable a significant increase in the proportion of recycled materials in the production process and make it possible to operate at high speed. Film damage is avoided, and a consistent, uninterrupted production is guaranteed. Tests with a 30 percent recycled content and the use of the polymer stabiliser have shown a reduction of film stippling by up to 25 percent.

Sustainable solutions are in demand not only for processors of packaging films, but also for manufacturers of plastic components for the transport or electronics industry, write the authors Dr. Diederik Cioyvaerts and Dr. Christian Battenberg (Global Segment Manager Processors, BL) in the trade journal "Plastverarbeiter 1/20". The focus is not only on the recycling of components, but also on the use of materials that contribute to improved sustainability. As a result, plastics are increasingly being used in transport applications to reduce the weight of the means of transport and their fuel consumption. Fibre-reinforced composites are increasingly being used for sophisticated components. In order to bring their advanced material properties further towards the required target values, various additives such as flame retardants are used. This is essential due to the high carbon and hydrogen content of the underlying plastics and the associated low flammability.

Sustainability Requires Flame Retardants In Fibre Composites

The weight of vehicles can be reduced by using flame-retardant fibre composites, also for structural components. Carbon fibre reinforced composites are used - such as thermoplastics, but especially thermosets, e.g. epoxy resin systems. These weight savings and the resulting increased range are a decisive advantage, especially for the constantly growing electric mobility. It must be taken into account that each individual application has different fire protection standards, which may even differ from country to country.

Flame retardants must therefore be carefully selected and matched to the system in question. According to the Swiss authors, the chemical nature of the flame retardant as well as its decomposition products in case of fire plus their interaction with the plastic influences the mode of action and effectiveness. Therefore, the selection of the appropriate flame retardant is not trivial - on the contrary, it requires a lot of testing, experience and chemical expertise.

As far as flame retardancy is concerned, halogen-free solutions used as additives are the benchmark today for preventing the spread of a fire or the ignition point of plastic components in an environmentally friendly way. In addition to the existing additive flame retardants, the market is showing an increasing demand for additives that are soluble and reactive in the resin. A great advantage is the slightly increased viscosity compared to powdery agents.

Effective Roof Sealing Through Coatings With Latex Impregnated Fleeces

Turning a flat roof into a waterproof roof, and keeping it tight for 20-30 years, is not necessarily an easy task. One of the most common solutions to create a waterproof barrier is to use polymer bitumen roofing membranes. These have been increasingly popular for years and are 'legitimate' successors to roofing felt thanks to their superior long-term performance.

Such roofing membranes essentially consist of two parts: a non-woven polyester fabric impregnated with latex, which is the actual carrier, and a top layer of bitumen for waterproofing. The bitumen also acts as a kind of adhesive to bond the fleece to the unprotected flat roof.

An important component of many of these polyester roofing membrane systems is synthetic latex to impregnate the fleece. The latex impregnation makes the fleece resistant to dimensional changes such as shrinkage and expansion (see DIN standard 18192) – which would otherwise lead to unwanted cracks and could destroy the waterproofing. These forces are caused by fluctuations in temperature, which vary between -40°C and +80°C due to the seasons and day and night cycles. A polymer-impregnated fleece is therefore much less susceptible to these dimensional changes. The latex also prevents water from penetrating the bitumen sheeting and thus prevents the sheeting from becoming delaminated – especially in frosty conditions. The cross-linking agent contained in the latex creates a three-dimensional link between the polymer chains before, during and after the evaporation of the water. This contributes to a balanced ratio of mechanical strength and hardness.

Advantages In Terms Of Environmental Compatibility – Reduction Of Formaldehyde Release

During the impregnation of nonwovens with typical chemical binders available on the market, formaldehyde is released by the cross-linking reaction. However, crosslinking is necessary – tantamount to the use of a polymer-impregnated nonwoven.

The latex also prevents water from penetrating into the bitumen sheeting and thus prevents the sheeting from becoming delaminated - especially in frosty conditions. The cross-linking agent contained in the latex creates a three-dimensional link between the polymer chains before, during and after the evaporation of the water. This contributes to a balanced ratio of mechanical strength and hardness.

Advantages in terms of environmental compatibility - reduction of formaldehyde release

During the impregnation of nonwovens with typical chemical binders available on the market, formaldehyde is released by the cross-linking reaction. However, crosslinking is necessary – as described – to achieve the required resistance and good thermal stability. New latex compounds are ammonia-free and do not contain formaldehyde-releasing crosslinkers.

Measurements show that the emission of the product not only meets the previous requirements of < 20 ppm/m3 exhaust air, but also stricter ones, such as the German Federal and State Working Group on Emission Control with 5 mg/m3 exhaust air (valid since February 2020).

In addition to a formulation that avoids the release of unwanted substances, modern polymers (such as the product 'Litex SkyShield') are also suitable for use as a 1 K system without thermoset resins. This leads to considerable cost savings, such as fewer logistics or reduced warehousing. Another advantage of the new polymer is that it allows the nonwoven to dry at much lower temperatures: The drying air can be reduced from typically 200°C to 170°C during the manufacturing process.

All this represents a significant economic benefit for the end-user compared to conventional technologies.

((From: nonwovens TRENDS 1/2020, authors: Michael Karnop, Andreas Gehr of Synthomer Deutschland GmbH, Marl/Germany))

Weserland can provide hands-on help in this area. We are looking forward to receiving your enquiries.

 

The German Federal Ministry Of Economics And Energy Supports A Project For The Development Of A Fully Recyclable Clean Floor Mat And A Process For Separating Raw Materials

Clean floor mats are used in entrance areas to remove dirt and moisture from shoe soles. A high-quality textile clean floor mat, also known as a dirt-trapping mat, usually consists of a rubber backing layer, a base of polyester fabric or fleece and a pile of polyamide yarn. As the rubber backing layer is firmly attached to the top side (carrier and pile), it is not possible to separate the individual components, e.g. after the mat has been used for a long time. Re-use of the raw materials is therefore impossible. For this reason, clean floor mats are usually sent for thermal recycling and valuable raw materials are burned.

In order to prevent this, the aim of the project 'Clean Floor Mat' („SauberKREISLAUFmatte") is to develop a recyclable clean floor mat. In addition, a process is being developed with which the individual raw materials can be returned to the recovered substance cycle. The qualified, safety-related and health-related properties of the new „SauberKREISLAUFmatte" must at least correspond to the state of the art.

 The project is funded by the Federal Ministry of Economics and Energy (BMWi). This will be indicated externally in all project-related presentations by a corresponding logo (BMWi logo with funding supplement).

RWTH Aachen University Tests 3-D Heat Insulation Textiles In Simulation

As part of the 'HEATex' research project, the Institute for Textile Technology at RWTH Aachen University developed heat-protective textiles as underwear. In addition to experimental tests, the heat transport properties of the multi-layer heat protection textile are simulated under the influence of contact heat. The simulation allows a qualified pre-estimation of the heat protection effect of different layer constructions. The simulation model was carried out with the simulation software 'Abaqus/CAE' of the Parisian software company Dassault Systemes SE.

With this approach, the costs and effort of future comparisons can be noticeably reduced. The results of the simulation model show a fundamental similarity to the experimental test results used so far.

Point of fact is that such textiles and materials are extremely important for about 10 per cent of the German workforce: At their workplaces they are exposed to high temperatures (metal, glass, ceramics and steel production as well as forges, foundries, fire departments). During their work assignments, they are regularly scalded and, in worst cases, suffer heat strokes, which occur at a body temperature of over 40 °C. Thermal protection textiles prevent direct contact between external protective clothing and skin and improve the absorption and transport of the body's own moisture.

How are the thermal protection textiles tested?

In the tests, the textile layers of the undergarments are assumed to be solid materials with isotropic material properties. Air inclusions within textile layers and the use of different materials in a layer are taken into account by adjusting the material parameters. Finally, averaged parameters are used. At 79.2 °C, the final temperature of the simulation is slightly higher than comparable final temperatures measured in in vitro tests with heat protection textiles using contact heat and without pressure. In reality, the textiles are actually surrounded by air. Circulation of the air on the textile caused by temperature differences leads to cooling of the textile by natural convection. This effect is enhanced by forced convection in the form of air movements in the test environment. Finally, according to the authors of the Institute of Textile Technology, a certain inaccuracy in the material parameters leads to the fact that the final temperatures from simulation and tests are of the same order of magnitude despite some simplifications.

With the help of simulation, textiles can be efficiently and quickly pre-estimated in a first step. In addition, the component-based structure of the simulation allows quick changes of material parameters or a change of the layer structure. All in all, this can be used to optimise the development of heat-protective clothing. If such a simulation is used, special attention must be paid to the accuracy of the material parameters used. Other physical effects, such as radiation influences, can be integrated into the simulation if these parameters are known. In addition, the authors recommend minimizing the required computing power by simplifying and exploiting symmetries in the geometry.

A detailed version by Kevin Krause, Paul Grünefeld, Lena Barth, Lukas Lechthaler, Christoph Peiner and Thomas Gries has been published in melliand Textilberichte 1/2020.

 

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