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Pultruded natural fibres for cleaner air

The four-year OSIRYS project is developing natural fibre-based composites for façades and interior partitions that will improve indoor air quality in both new builds and restoration projects. 

Indoor air quality and emissions from building materials are a major challenge, says Inmaculada Roig Asensi, head of the Composites Department of Spanish research organisation AIMPLAS, a partner in the project. 

There is currently a growing trend of replacing traditional construction materials, which contribute to contaminants such as VOCs, formaldehyde, particulates and brick fibres, with multilayer façades offering several advantages.

In addition to environmental benefits, many new building envelope improvements result in lower energy bills, as well as improved thermal comfort and moisture and noise control.
From a construction point of view, the use of a modular panel structures with no water required for their assembly also allows shorter installation times and easy maintenance while the façades are also lighter.

Previous studies have shown that biocomposites offer a sustainable alternative to traditional polymers and composites. Their advantages include, low fibre density, recycabilit and lower energy consumption in their production.

Within the OSIRYS project, new pultrusion biocomposite profiles have been obtained to replace typical light gauge steel products. These profiles can also be used to finish existing masonry partition walls, cladding mechanical and extraction shafts and column cladding. The profiles have been designed to be processed from a bio-based epoxy resin and using flax and glass fibres as reinforcements. They have been integrated into a  modular multi-layer envelope.

Testing
A new concept for testing building materials with respect to good indoor air quality is being developed and tested as part of OSIRYS by the IVL Swedish Environmental Research Institute. The testing concept consists of evaluation of the material with respect to primary emissions of VOCs and secondary emissions –reaction to products after exposure of the material to ozone, deposition velocity of ozone and microbiological resistance.

The emission of the VOCs is being evaluated according to the German evaluation scheme AgBB: Health-related evaluation of emissions of volatile organic compounds (VOC and SVOC) from building products.

Indoor ozone may react on the surfaces of a material and can lead to elevated concentrations of oxidized products. The new material provides an opportunity for passive reduction of indoor ozone. Ozone deposition velocity describes a materials’s ability to destroy ozone. Resistance to microbiological activity is also being tested in another experimental set-up.

Processing
Processing biocomposites is complex and low output and there is a need for new technologies adapted to the behaviour of the bio-based materials. Biocompositesthermoset profiles have been developed at pilot plant level and continuous natural fibres with low twist have been employed for profile manufacturing.

A homogeneous curing, minimised residence time and processing temperature are required to improve formulations with bioepoxy and natural fibres. For this, specific characteristics of the new bioresins have been  assessed in respect of:

Evaluation of curing cycle of selected bioepoxy, taking into account requirements in terms of temperature for the processing of natural fibers at 160ºC).
Differential Scanning Calorimeter (DSC) and Dynamomechanical analyzer (DMA) tests to ascertain the maximum temperatures to optimise glass transition temperature (Tg) results.
The adaptation of the pultrusion process to biocomposites with natural fibres yarns has been required to improve formulations and process parameters to avoid fibre breakages. A post curing area has been added to the pultrusion equipment to adapt to requirements of bioepoxy resin in terms of post-curing.

Different trials of pultrusion with glass, flax and hybrid (glass and flax) fibres have been carried out with standard polyester resin and bioepoxy resin in order to optimise processability.
Pultrusion profiles were prepared for mechanical characterization according to ISO 10406-1:2008 standard.