Influence of nanofillers on thermal insulating properties of polyurethane nanocomposites foams

Abstract

The effect of several nanofillers on thermal insulating properties of polyurethane rigid foams (PUR) was analyzed. The nanofillers used differ for chemical nature and aspect ratio. We used both pristine and organically-modified layered silicates (OMLS) and inorganic spherical nanopowders. The fillers were first dispersed in the polyol component through use of sonication; then doped polyol was mixed with isocyanate. The effect of polyol viscosity and nature (polyether or polyester) on the degree of the dispersion of the filler was also taken into account. The results obtained showed that the chemical nature and viscosity of polyols as well as the kind of compatibilization of the filler play a very important role in favoring the filler dispersion on a nanometer scale; the aspect ratio of the filler is instead not so important. When a good degree of dispersion is achieved, the thermal insulating properties of the foam can be slightly enhanced, as the fillers may act as nucleating agents. Some drawbacks were also found in using nanofillers: the fillers may bring in some cases an increase of the open cell content making the diffusion rate of the blowing agents faster thus leading to a worsening of thermal insulating properties during time.

How much do nanoparticle fillers improve the modulus and strength of polymer foams?

“…Nanofiller can have numerous other beneficial effects: nucleating foam bubbles, 47,51,52 decreasing the cell size, [53][54][55] acting as diffusion barriers, 56-58 increasing electrical conductivity, 59,60 stabilizing the foams through interfacial adsorption, 61 stabilizing foam through reduced crystallinity, 62,63 improving fire retartance, 64 reducing thermal conductivity, 65,66 and increasing open cell content. 48 For some of these properties, the questions central to this review may be posed, e.g., how much does thermal conductivity reduce once samples are compared at the same foam density?…”

“…6,25 The solid lines correspond to envelopes of closed and open-celled foams from Gibson and Ashby. 65 improvement can be realized. Since the material comprising the cell walls of the foam is a nanofiller-reinforced composite, this suggests that nanofillers are likely to be more effective at modifying the properties of foams made from low-modulus polymers.…”

The Effects of Functionality of the Organifier on the Physical Properties of Polyurethane Rigid Foam/Organified Nanosilica

“…With increasing modified nanosilica content, cell density was increased and cell size was reduced. Small amounts of nanoparticles in the polymer may serve as nucleation sites to facilitate the bubble nucleation process and produce a finer cell structure [12]. Also, N f almost was higher in NCAEAP, which showed better dispersion of nanoparticles in the PU matrix because of the stronger interaction.…”

Nanoki̇l Ve Kabaran Alev Geci̇kti̇ri̇ci̇ İlavesi̇ni̇n Ri̇ji̇t Poli̇üretan Köpük Malzemeleri̇n Isil Bozunma Ve Yanma Davranişlarina Etki̇leri̇ni̇n İncelenmesi̇

“…Bununla birlikte, NCL oranının % 10 ve % 15'e yükselmesi ile ısı iletim katsayılarında sırasıyla yaklaşık % 2,4 ve % 12,9 oranında artış tespit edilmiştir. % 15 NCL ilaveli poliüretan köpük malzemenin ısı iletim katsayısında dikkate değer artış, bu oranda kil ilavesinin köpük malzemedeki hücre boyutundaki artışa (Şekil 4) ve kapalı hücre sayısındaki azalmaya sebep olması ile açıklanabilir [21,23,32,39]. Poliüretan köpük malzeme içerisine dolgu maddesi olarak ilave edilen kil oranının artmasıyla köpük malzemenin hücre duvarları arasına yerleşen kil nedeniyle hücre duvarları daha zayıf ve ince hale gelerek daha kolay kırılmaktadır.…”