Production Processes 

Impregnation

A key driving force behind building with wood is to reduce environmental footprints of construction. Impregnation is chosen as the method to embed the bioPCMs into the solid wood and fibers as it has various advantages including the ability to control parameters such as vacuum depth, pressure, duration and temperature.

Impregnation allows the bioPCMs to penetrate deep into the wood structure, reaching the inner layers and enhancing the effectiveness of the phase change materials. By impregnating the wood, desired properties such as pressure and durability are enhanced, making it a well-suited application, ensuring optimal results and performance. Additionally, compared to surface treatment, impregnation requires less chemical usage, reducing environmental footprints and minimising exposure to harmful substances.

In BIOBUILD, solid wood flooring and wallboards are targeted as bio-based building material. In modern buildings, flooring is an improved alternative to commonly used materials such as carpets, laminates and ceramics. The wood flooring is designed as a parquet consisting of a softwood-core layer placed between the bottom layer and upper surface layer. It is the core layer that is impregnated with the bioPCM and glued to the other layers using conventional glueing systems as well as the developed bio-resins. The wood fibers are also impregnated with the bioPCMs and bonded into bio composites to produce the wallboards. The impregnation parameters will be optimised to achieve the optimal bioPCM impregnation into fibers.

Wood Controls without BPCM (slide 1) / Wood Controls Impregnated with BPCM (slide 2) © SLU

The ThermoVuoto Process

The major challenge to be addressed during the production processes is the potential leaching of bioPCMs from solid wood and fibers. To mitigate this issue and eliminate the leaching, BIOBUILD will employ thermal modification. The aim of thermal modification is to enhance the permeability of wood, improve retention of impregnated bioPCMs, increase dimensional stability by reducing absorption and enhance durability against biodegradation.

This eco-friendly process used in the project is known as ThermoVuoto, a technology that involves thermal modification of wood. This process differs from traditional thermal modification methods by substituting oxygen inside the reactor with a partial vacuum. As a result, it alters the wood heating conditions, leading to specific changes in its structure and properties.

During the ThermoVuoto process, wood undergoes thermal treatment in the absence of oxygen which can result in the degradation of certain chemical compounds in the structure of the wood ultimately, altering the fiber cell walls. The technology is designed to provide an eco-friendly and efficient method for enhancing such properties of wood, improving its permeability, increasing the retention of bioPCMs, ensuring a stronger hold following the impregnation.

Plant Oil Resins, BIOBUILD Project

Working Mechanism of Phase Change Materials © SLU

The Microwave Approach 

The microwave (MW) approach is another method used to improve the bioPCM retention and eliminate leaching. This method is used primarily to increase the permeability of refractory wood species to facilitate enhanced impregnation by precisely controlling the drying process and modifying the wood structure, making it more receptive to bioPCM.

Microwave radiation penetrates materials and generates heat through energy absorption by polar molecules within the material. By using the microwave approach, wood can be dried to a specific moisture content, which is crucial for impregnating it with bioPCM and preventing leaching. In BIOBUILD, pine, beech and poplar undergo irradiation before bioPCM impregnation.

Before manufacturing the composite, the impregnated solid wood and fibers undergo leaching tests. This process involves subjecting the materials into multiple thermal cycles to simulate real working conditions. The testing is done to optimise the bioPCM aiming to eliminate leaching based on the results obtained from the leaching procedure.

Plant Oil Resins, BIOBUILD Project

MW Treatment on Wood Cell Wall © SLU

BPCM (ethyl palmitate (EP) ester) in wood composites
during releasing heat © SLU

BPCM (ethyl palmitate (EP) ester) in wood composites
during absorbing heat © SLU

Bio-binders

Once the bioPCMs are impregnated into the solid wood and the parquet layers are glued, the impregnated wood fibers must be bonded to form bio composites. These bio composites are used as wallboards or integrated into other building elements. The impregnated wood fibers will be processed into bio-composites using only bio-binders. BIOBUILD showcases three bio-binders: plant oil resins, lignin and fungal mycelia.

Novel Materials with Thermal Energy Saving Functions produced in laboratory scale at SLU, BOKU and CNR-IBE;
a) parquet; b) wood composite with spruce pulp fibres; c) bio-composite with wood particles and recycled paper fibres; d) bio-composite with wood particles and mycelia.
© SLU

Plant Oil Resins

The first bio-binder is a resin made of plant oil. Plant oils serve as starting materials for polymer synthesis due to their widespread availability, inherent biodegradability and minimal toxicity. Traditionally, the processing required high curing temperatures and lengthy durations, rendering it unsuitable for processing bioPCM fiber composites due to the risk of leaching.

In BIOBUILD, a newly developed fast curing epoxy resin is being adopted, obtained through a single-step process at room temperature. The resulting materials are plant oil resins as binders with favorable mechanical properties.

Lignin

The second bio-binder is made of lignin that serves as a substitute for fossil-based binders mainly, formaldehyde-based binders. In BIOBUILD, an established technology is used to produce the lignin-based binders.

Unlike previous methods that required incorporating secondary polymers, the enzyme-based system employs laccases and an efficient oxygen supply to produce highly polymerised lignodulfonates with high quality adhesion properties, replacing the use of toxic agents.

Fungal Mycelia

The third bio-binder relies on the growth of fungal mycelia. Wood decay fungi is bound by strong mycelia which bind the dispersed fibers and serve as a matrix medium within the composite. The amount of bioPCM impregnated will be optimised starting from 30% into the mycelia composite. The composite will be moulded in a desired shape and dimensions of the final wallboard; the mycelia are left to colonise the fibres in a controlled environment for three weeks. After the colonisation process is complete, the panel is demoulded, dried and finished.

The bio-composite moulding process with the three binders is studied in terms of temperature, pressure and duration of pressing. X-ray micro-tomography is employed to perform detailed characterisation of the internal structure of the most promising lightweight bio-composites obtained for each bio-binder. To meet European safety standards, the produced bio-composites fulfil European class E for fire resistant wood products. To further achieve this, a sustainable and non-toxic flame-resistant solution is used in the bio-composites as an additive.

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Eco-friendly Materials

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Testing