Material PropertiesMeasurement of thermal conductivity of hollow glass-bead-filled polypropylene composites
Introduction
Foamed plastics are commonly used as thermal and sound insulation materials. However, their application is limited due to poor mechanical properties. There is, therefore, a focus to fabricate a kind of light, porous plastic with better mechanical strength and good thermal and sound insulation properties. Rigid hollow micro-spheres (e.g., hollow glass beads (HGBs), hollow ceramic beads, rigid hollow plastic beads, and so on) containing inert gas have some advantages, such as low thermal conductivity and are lightweight. In addition, these micro-particles do not generate important stress concentration at the interface with the matrix owing to their smooth spherical surface. When they are used to fill and modify resins, polymer/hollow micro-sphere composites with thermal and sound insulation ability, light weight and good mechanical properties may be prepared [1]. This kind of composite is applied in building materials, space-flight and the aviation industry.
The effective thermal conductivity is an important heat transfer property of materials. The heat transfer process of porous materials is very complicated, especially for polymer composites. It is quite important, therefore, to understand the mechanisms of heat transfer in polymer composites. For porous materials, several researchers [2], [3] have derived effective thermal conductivity equations based on the Maxwell expression, or established a more accurate formula for calculating the effective thermal conductivity of porous materials [4]. The models proposed respectively by Nielsen [5] and Cheng-Vochon [6] can better estimate the effective thermal conductivity of filled composite materials, while the Agari–Nagai equation can predict the effective thermal conductivity of composites with high-loading [7] Liang [8] analyzed the thermal conductivity of a porous material with closed spherical and cylindrical holes. Suvorov et al. [9] studied the thermal conductivity of hollow emery-filled composites.
Generally, measuring the thermal conductivity accurately is helpful to study the heat transfer process and mechanisms in composite materials. The objective of this work is to measure the thermal conductivity of HGB-filled polypropylene (PP) composites and to determine the effects of the content, size and its distribution on the thermal conductivity of these materials.
Section snippets
Raw materials
An injection grade of PP with trade mark CJS-700, supplied by Guangzhou petrochemical Co. Ltd in China, was used as the matrix resin. The density and melt flow index (230 °C, 2.16 kg) of the resin were 0.91 g/cm3 and 12 g/10 min, respectively.
Two kinds of HGBs supplied by Molüs Company in Germany, TK35 and TK70, with different sizes were used as the fillers in this work. The mean diameters of the fillers were 35 and 70 μm, and the densities were 0.68 and 0.21 g/cm3, respectively. The surface of the
Particle size distribution
It is generally believed that particle size and size distribution of fillers are important parameters for affecting physical properties of composites. Differential distribution (λ) is an important parameter characterizing the particle size distribution of fillers. The higher the value of λ in a given range of particle diameter, the narrower the particle size distribution is. Fig. 2 shows the relationship between the differential distribution and the bead diameter of TK35. It can be seen that
Conclusions
The heat insulation property of polymeric materials may be improved by filling with inorganic hollow micro-spheres. Under the experimental conditions, the effective thermal conductivity of hollow glass-bead (HGB)-filled polypropylene (PP) composites decreased roughly linearly with increase of the volume fraction of the beads.
It is beneficial to improve the heat insulation property of the polymer composite systems if the size of the HGBs is relatively large and the distribution of the beads in
References (9)
Tensile and impact properties of hollow glass bead-filled PVC composites [J]
Macromol. Mater. Eng.
(2002)Principles of heat flow in porous insulation [J]
J. Am. Ceram. Soc.
(1935)Conductivity of multicomponent systems [J]
J. Am. Ceram. Soc.
(1959)A theory of thermal conductivity of porous materials [J]
J. Am. Cream. Soc.
(1954)
Cited by (120)
Mechanical and thermal insulation performance of hollow glass microsphere (HGMS)/fumed silica/polyester microcomposite coating
2023, Progress in Organic CoatingsA review on cement-based materials used in steel structures as fireproof coating
2022, Construction and Building MaterialsEpoxy-matrix composite with low dielectric constant and high thermal conductivity fabricated by HGMs/Al<inf>2</inf>O<inf>3</inf> co-continuous skeleton
2021, Journal of Alloys and CompoundsCitation Excerpt :Regarding electronic packaging substrate materials, it requires not only low Dk, but also a superior heat dissipation capability. Paradoxically, the thermal conductivity (TC) of air is very low, which can inevitably deteriorate the matrix TC by introducing pores into polymer intended for a lower Dk [27–29]. High TC fillers can effectively enhance the heat dissipation ability of composites, but usually at the cost of high loading [30].
Effective thermal conductivity changes of the hydrate-bearing quartz sands in depressurization and soaking
2021, Journal of Natural Gas Science and Engineering