Effects of nucleating agents on the morphological, mechanical and thermal insulating properties of rigid polyurethane poams

Abstract

This study examined the effects of liquid and solid additives on the morphological, mechanical and thermal insulating properties of rigid polyurethane foams (PUFs). The PUFs synthesized with tetramethylsilane (TEMS) as a liquid-type additive showed a smaller average cell size and lower thermal conductivity than those with the aerosil 200 and clay 30B as solid-type additives. When TEMS was added, the average cell size of the PUF became more uniform and finer due to the reduced surface tension of the polymer solution, which increased the nucleation rate and number of bubbles produced and reduced cell size. The PUFs with TEMS showed the highest closed cell contents among the PUFs prepared using TEMS, aerosil 200 and clay 30B. This suggests that the insulation properties of PUF can be determined by both the size of the cell structure and the amount of closed cell contents in the system. The compression and flexural strengths of the PUF increased slightly when the aerosil 200, clay 30B and TEMS were added compared those of the neat PUF. The reaction profiles of the PUFs showed a similar gel and tack free time with the reaction time among the PUFs synthesized with three different additives and neat PUF. This suggests that the nucleating additives used in this study do not affect the bubble growth of the chemical reaction, and the additives may act as nucleating agents during the formation of PUF. From the above results of the cell size, thermal conductivity, closed cell contents and reaction profile of the PUFs, liquid-type nucleating agent, such as TEMS, is more effective in decreasing the thermal conductivity of the PUF than solid-type nucleating agent, such as aerosil 200 and clay 30B.

Hydration-induced reinforcement of rigid polyurethane–cement foams: mechanical and functional properties

“…To overcome this problem, in the scientific and technological literature, there can be found numerous strategies aimed to the increase of the mechanical properties of PU foams, mostly by filling the polymeric matrix with a rigid phase. Reinforced PU foams have been prepared with several kinds of fillers, such as glass fibers [3,4], nano-silica [5,6], wood flours [7], clays [6,8], and carbon powder [9]. These studies point out the problem of adhesion between the polymeric matrix and the filler for mechanical applications.…”

“…Thus, while the filler may act to stiffen the foam, the individual particles can act as pre-existing flaws, allowing for easier crack initiation and propagation, thereby decreasing deformation and strength. Pre-treatments of the filler have been successfully performed to improve the adhesion [2, 5,6,8] although increasing material cost.…”

Recent Developments of Foamed Polymer/Layered Silicates Nanocomposites

“…The mechanical properties of rigid polyurethane foams increase with a small addition of the layered silicate and reach the maximum value at clay content of 2-3 wt % [19,20,22]. On the other hand, the thermal conductivity of the composite foams is lower than pristine foam due to the decreased cell size and increased number of cell [21].…”

“…This process can result in a broad cell size distribution, because the cells do not generate simultaneously. The shortening of the nucleation time interval yields a narrow cell distribution in microcellular foams, because the cell nucleation rate increases [19,78,89,100,101]. The application of super critical fluids (SCFs) to the preparation of foams leads to reduction of matrix viscosity and/or helps to nucleate nanoscale bubbles.…”

Crystallization behavior and physical property of poly( ε ‐caprolactone) tailored by a biocompatible linear diamide nucleating agent

“…erties of composite materials are affected by many factors, such as the additive and its content of the NA. [40] The enhanced elongation at break of the PCL maybe associated with the uniform dispersion of the EBH in the PCL matrix and strong interfacial adhesion (entanglement of the molecular chain) between the PCL and EBH, [41] resulted from their hydrogen bond interaction. Similar result was reported in the poly(L-lactide) (PLLA)/modified nanoparticile of magnesium oxide (m MgO NPs)…”