Biocomposites With Good Outdoor Durability
Biocomposite with good outdoor durability – coatings for outdoor use.
Durability is one of the key issues in the development of fibre reinforced polymer composites for construction.
Since the application of FRP in the construction industry is quite recent, there is little knowledge of the short and long term behaviour of these materials. The durability of FRP structures depends both on specific environmental conditions (alkalinity, moisture, temperature) and long term effects (creep and relaxation, fatigue loading) among others.
One of the objectives of the OSIRYS project is to minimise the influence of environmental factors and improve bio-composites outdoor durability. To that end, several protection strategies are now commercially available and will be tested during this project.
All these efforts are moving towards the objective of increasing the use of bio-composites in the construction market and to obtain more market penetration by manufacturing components that fulfil all the technical requirements from this very demanding market.
There are two main ways to improve outdoor performance of composite materials. Either applying an external protection layer (coating) on the exposed surface or modifying the resin formulation, adding additives to bring intrinsic properties to the matrix. In OSIRYS it was decided to apply external coatings to protect the bio-composite against deterioration caused by external factors such as UV rays, wind, rain and thermal changes, reducing maintenance and increasing the life of the building.
On the basis of a deep analysis of most of the state of the art products commercially available, six coatings were selected taking into account several factors such as design requirements, process requirements (processability, price) and service conditions (service temperature, humidity degree). These coatings were applied by a roller on bio-composite laminates, see figure below.
Compatibility and performance of the coatings with the raw materials selected to fabricate the bio-composite laminates was evaluated by means of several tests, following either ASTM or EU standards (adhesion test, abrasion test, impact test). A summary of the results obtained from all the tests carried out on the selected coatings can be found in the table (right).
From these results it is clear that most of the coatings showed good impact and abrasion resistance and adhesion to the substrate. However, selection of the most appropriate coating depends also on the final application and additional testing is needed, such as:
- Durability test to identify the colour, gloss and mechanical properties lost when the coated material is exposed to different climatic conditions: for that, accelerated tests are carried out using a QUV testing machine.
- Fire test to investigate fire performance of the samples and check whether or not they fulfil the requirements for an exterior façade (cone calorimetric test).
Regarding the durability test, all the relevant standards for coatings and composite materials were identified in order to select the most appropriate ones for the product.
In addition, the study of the climatic conditions of different European countries was done to define the most appropriate testing conditions for carrying out the accelerated weathering tests in the QUV.
Preliminary results on OSIRYS laminates are shown in the image. Laminate 1 is a non-coated sample and is used as a reference. Laminates 2 and 3 were coated with two different transparent fire retardant coatings. The coated samples remain unchanged from their initial appearance after the first 500 hours of the test. The most severe changes were observed for the uncoated sample including a loss of colour, brightness and original appearance.
So, as expected, the use of coatings helps to improve the outdoor durability of the bio-composites.
The task now is to quantify and optimise the coatings.