The effects of hygrothermal exposure on the thermal conductivity, mechanical properties and density of nanocellulose based foams
Creators: name: LaMarche, Whitney Marie
Publisher: name: Washington State University
Year: 2019
Subjects: Foamed materials--Effect of high temperatures on
Cellulose nanocrystals--Effect of high temperatures on
Cellulose insulation--Effect of high temperatures on
Foamed materials--Thermal properties
Cellulose nanocrystals--Thermal properties
Cellulose insulation--Thermal properties
Foamed materials--Mechanical properties
Cellulose nanocrystals--Mechanical properties
Cellulose insulation--Mechanical properties
Hygrothermoelasticity

description: Petroleum-based insulation materials, including polymer foams, depend on global resources, have high transportation costs associated with manufacturing, and are habitually non-biodegradable/recyclable. During foam fabrication, the use of harmful chemicals in the manufacturing process chemistry has caused direct acute toxicity to the workers as well as harmful impacts to the environment. With a global shift from reusable to single use containers, the plastics market currently accounts for over 275 million metric tons of waste, of which an estimated 8 million accumulate annually in the oceans. These issues have led to a heightened demand for more environmentally friendly materials and processes for insulation and packaging applications, driven by eco-conscious consumers and increased global regulations against petroleum-based plastics. This brands bio-based insulation materials a viable alternative in the global market. Cellulose-based foams are a greener replacement opportunity over traditional synthetic insulation materials. Composite foams of nanocrystalline cellulose (NCC) and polyvinyl alcohol (PVA) have shown replicable thermal and mechanical properties. Unfortunately, one of the challenges associated with cellulose-based foams is their susceptibility to moisture, especially at elevated temperatures. Theoretically humid environments soften the polymer matrix reducing mechanical strengths and increasing elasticity This work shows further investigation into 1,2,3,4-butanetetracarboxylic acid (BTCA) cross-linking of NCC-PVA isotropic foams and their respective thermal and mechanical properties. Various freezing temperatures and freezing techniques were tested to find the optimal samples with the best mechanical properties. Low density foams of 0.019 g/cm3 were achieved with an average thermal conductivity of around 20 mW/mK. Cellulose foams were then exposed to three relative moisture environments at 40 °C for up to twenty-four hours to test their integrity under hygrothermal degradation. Thermal insulation properties were retested post exposure to 77, 82, and 96 percent relative humidity (RH). It is reported in this work that the thermal conductivity and apparent density of the foams remain unchanged after extreme moisture exposure. However, the mechanical strength and modulus decrease at different rates upon exposure to different humidity levels. Such changes were related to the chemical interactions of the polymer matrix with cations of saturated salt solutions, as demonstrated by SEM-EDS.