Halloysite Containing Polyurethane Foams as Insulation Materials with Enhanced Flame Retardance

Deniz Anıl

Materials Science and Nanoengineering, MSc. Thesis, 2019

Thesis Jury

Asst. Prof. Serkan Ünal (Thesis Advisor), Prof. Dr. Kürşat Şendur (Thesis Co-Advisor), Prof. Dr. Yusuf Menceloğlu, Asst. Prof. Bekir Dizman, Assoc. Prof. Engin Burgaz

Date & Time: July 16th, 2019 14:00

Place: KTMM

Keywords: Rigid Polyurethane Foams, Halloysite Nanotubes, Thermal Conductivity, Flame Retardancy

Abstract

Rigid polyurethane foams (RPUFs) are one of the high-performance insulation materials preferred due to their superior thermal insulation properties, good chemical durability, high mechanical strength and easy processability. Nevertheless, RPUFs have low thermal stability and are highly flammable, which is a critical concern in insulation applications. Conventionally, flame retardants (FRs) are used to overcome these problems. These materials help the formation of a stable char layer on the exposed surface and scavenge flammable radicals released from the burning substance. However, these FRs need to be added in high amounts to provide acceptable flame retardancy and are usually not environmentally friendly. FR chemicals can be partially replaced by alternative additives to provide safer flame retardancy. Halloysite nanotubes (HNT) are low cost, abundant clay minerals, standing as a unique, environmentally friendly alternative to numerous synthetic nanofillers. During burning, HNTs can reinforce the char layer and entrap flammable decomposition products. It can contribute to the formation of smaller cells in RPUF matrix, to reduce thermal conductivity. Like other polymeric nanocomposites, it is critical to obtain a homogeneous dispersion of HNTs in the RPUF matrix.

In the first part of this thesis untreated and sonicated HNTs were incorporated into RPUFs. Thermal conductivity of these nanocomposite foams was studied both experimentally and theoretically, followed by preliminary flame retardance tests. In the second part, FR-loaded and silane-functionalized HNTs were added into RPUF formulation. Halogenated FR content in the RPUF formulation was partially replaced with functionalized HNTs, which resulted in nanocomposites with comparable total heat release and peak heat release rates to existing commercially available RPUFs with higher halogenated FR content. The incorporation of HNTs into these RPUF matrices resulted in slightly increased time to ignition and higher residual mass.