Date of Award

Summer 8-16-2024

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Forest Resources

Advisor

Ling Li

Second Committee Member

Benjamin Herzog

Third Committee Member

Samuel Glass

Additional Committee Members

Douglas Gardner

Stephen Shaler

Abstract

This study aimed to characterize the hygrothermal and material, i.e., physical and mechanical, properties of wood fiber insulation (WFI) that can be an alternative to fossil-based building insulation, targeting structural insulated panels, retrofit insulated panels, and a novel all wood structural insulated panel. The hygrothermal properties of rigid WFI boards with varying densities, 110, 140, and 180 kg/m3, and one 140 kg/m3 without paraffin wax treatment were evaluated following relevant ASTM standards. The hygrothermal properties measured were, porosity, water vapor transmission, liquid water absorption, and thermal conductivity at varying temperatures. Additionally, the Tensile strength and block shear strength of WFI bonded to lumber, OSB, and WFI was evaluated using three different structural adhesives to select one adhesive for further prototyping. The porosity of the WFI varied from 85-92% and is primarily impacted by density and not the presence of wax in the composite. The permeability of the WFI ranged from 65 ng·s-1m-1Pa-1 to 90 ng·s-1m-1Pa-1 depending on the samples’ density. Liquid water absorption on a % volume basis ranged from 2.5 – 20%, both wax and density were impactful to the results. Thermal conductivity coefficient (λ), ranged from .038 - .055 W/(m·K) depending on moisture content, average temperature, and density. 140 kg/m3 WFI with wax was selected as a representative material for the mechanical property testing of WFI laminated to other substrates. The tensile-perpendicular to grain bond strength was 10-16 kPa with substrate being more impactful than adhesive type. The shear strength was 60-90 kPa again with substrate being more impactful than adhesive type. For all tests the primary failure occurred within the insulation substrate illustrating the strength of the composite was not controlled by the adhesive layer but instead the insulation lamina itself. The results of this body of work establish that all wood structural insulated panels have the potential to succeed when used properly as a component of novel bio-based buildings based on their competitive hygrothermal properties and no immediate issue presented in using construction adhesives to manufacture the panels. However, the work also shows that bio-based materials are variable and complex in their composition and interaction with the environment. Rigorous testing will be required to fully predict how WFI will perform in-situ in various climates and in more complex assemblies.

The built environment is one of the leading contributors to global CO2 emissions and this margin is projected to grow. The materials that are used to construct a building are a major component of the associated carbon of a building. They represent the majority of embodied carbon and contribute to the rate at which operational carbon is generated. High performance, renewable, and carbon sequestering materials will be critical as the world continues to develop and demand more housing. This study reports the continuation of the development of a wood fiber-insulated panel (WIP) that offers a high-performance envelope without requiring hydro-carbon materials, by utilizing an all-wood design constructed with adhesives as opposed to mechanical fasteners. This design eliminates the cost and thermal reduction associated with the fasteners while retaining thermal performance. To this end, a WIP prototype was developed and manufactured along with two control wall assemblies: a similar wall assembly to the WIP with fasteners instead of adhesive (to laminate the WIP components), and an assembly made with polystyrene insulation. These assemblies were then evaluated in a simulated winter environment in climate zone 6A for hygrothermal performance. Temperature, relative humidity, and moisture content data were collected throughout the panels, and heat flux measurements were used to evaluate the impact of the fastener penetrations on thermal bridging. The WIP panels were found to perform as well or better than the control panels when evaluated for moisture interactions and insulative performance. Primarily, the use of structural adhesives within the assembly did not create a location where moisture accumulated. The mechanically fastened wood insulated panels performed well and managed bulk moisture very effectively. The polystyrene insulated panels performed well thermally but had high moisture levels between layers of insulation. Through these results it can be seen that a prefabricated all-wood panel could be successfully implemented as a high performance and environmentally friendly solution to growing housing demands and the requirements for more efficient buildings. Further analysis of the life cycle of these panels and complex hygrothermal simulations to investigate other potential designs and climate zones will be necessary to further develop this product.

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