Syntactic Foams with Poraver® as cellular filler
13,400 m² expanded glass acoustic ceiling for the Louvre Abu Dhabi
17. January 2019
Foto: Die hierarchische Rippenstruktur von Smart Slab
World’s first ceiling made of lightweight concrete and formwork of 3D-printed sandstone – Smart Slab DFAB House
23. January 2019

Reduced component weights, increased specific strengths and reduced thermal conductivity with Poraver® expanded glass Reduced component weights, increased specific strengths and reduced thermal conductivity with Poraver® expanded glass


Composites combine the positive properties of the starting materials to increase the performance of the resulting material. Poraver® expanded glass is lightweight, temperature stable and variable in processing, making it the ideal lightweight filler for a wide range of applications.

Depending on the application, porous fillers are used in cellular composites to reduce density, to enhance strength and other physical properties or to reduce the cost of the part. Ideally, one filler will effect all points and additionally is easy to process.

The multicellular expanded glass granule Poraver®, which is resource-saving produced from recycled glass, is since many years successfully used as a lightweight aggregate in various applications – from insulating materials and concretes to fire prevention.

At cellular composites, the particular challenge is to achieve better or optimum mechanical properties at lower density – or to be more precise, a lower component weight. A syntactic foam is used to demonstrate the suitability of Poraver® for this purpose.

Casting and infiltration processes - variability in production

In general, syntactic foams can be produced with Poraver® using both, casting and infiltration processes. Due to the spherical shape (sphericity of grain size 0.5-1.0 mm on average 0.97) and the available grain sizes, medium (Fig. 1) to very high filler contents are possible. The aim is to achieve a homogeneous structure. At a high content of Poraver®, it is advisable to fill a closed mould with Poraver® under maximum space filling and infiltrate the resulting voids with the matrix material of choice in a second step. For the casting process, the expanded glass can be homogeneously mixed into the resin within a short time, e.g. with a dissolver.

For the investigations shown here, the casting method was chosen to prevent the other filler (limestone powder) from floating and to obtain test specimen, which are as isotropic as possible. The samples consist of 40 vol.% binder (polyester resin) and 60 vol.% filler. The filler content contained successively more Poraver® expanded glass. Since limestone powder is not a porous material, the reference sample without Poraver® does not represent a syntactic foam. It serves to highlight possible advantages of a cellular composite material compared to standard materials.

Not only an improved density

Due to the increasing volumetric proportion of Poraver® expanded glass with a grain size of 0.25-0.5 mm (density 0.68 g/cm3), the density of the syntactic foam can, as expected, be significantly reduced. Soley with expanded glass of this grain size as filler, the density is only 0.8 g/cm3 and is thus significantly lower than that of the epoxy resin (approx. 1.1 g/cm3).

With the density, the strength of the system is reduced. The reference sample with a density of 2.1 g/cm3 achieves an average flexural strength of 38 MPa. The specimen with a density of 1.0 g/cm3 withstands a flexural load of 22 N per square millimetre. However, in the selection of a material its specific strength is decisive. Calculating these, the trend reverses and an increase with decreasing density becomes apparent (Fig. 2). The syntactic foam with a density of 1.0 g/cm3 achieves a specific strength that is more than 20 % higher compared to the reference.

Another positive effect of reducing density is the decreasing thermal conductivity. Comparing the samples without and soley with expanded glass reveals a density reduction of 62 %, which causes a decrease in thermal conductivity from 0.78 W/(m·K) to 0.16 W/(m·K). This corresponds to a reduction of 79 %.

Price and performance add up

At several Euro per kilogram, the price of pure resin is significantly higher than that of Poraver®. In addition, syntactic foams with expanded glass show good strength even with a lower resin content. Therefore, the material costs for a resin-bonded part can be reduced by using Poraver®. Even in comparison to comparable fillers for the production of syntactic foams, such as hollow glass microspheres, Poraver® is a more cost-effective alternative.

Versatility in application

Due to the high temperature resistance of the expanded glass, there is also the possibility of infiltration with thermoplastics and molten metals such as aluminium or zinc. Due to the large selection of matrix materials, a multitude of application areas and forms are possible. Walls of liquid heat accumulators, car body components and support cores can be cited as examples.

Foto eines zellularen Verbungwerkstoffs mit Poraver
Fig. 1: Section of a cellular composite made of Poraver® in epoxy resin matrix at medium filler content
Chart
Fig. 2: Change in strength and thermal conductivity over density of syntactic foams with Poraver® compared to the reference without Poraver® (density 2.1 g/cm3)

20 % higher specific strength with Poraver® expanded glass

Due to the increasing volumetric proportion of Poraver® expanded glass with a grain size of 0.25-0.5 mm (density 0.68 g/cm3), the density of the syntactic foam can, as expected, be significantly reduced. Soley with expanded glass of this grain size as filler, the density is only 0.8 g/cm3 and is thus significantly lower than that of the epoxy resin (approx. 1.1 g/cm3).

With the density, the strength of the system is reduced. The reference sample with a density of 2.1 g/cm3 achieves an average flexural strength of 38 MPa. The specimen with a density of 1.0 g/cm3 withstands a flexural load of 22 N per square millimetre. However, in the selection of a material its specific strength is decisive. Calculating these, the trend reverses and an increase with decreasing density becomes apparent (Fig. 2). The syntactic foam with a density of 1.0 g/cm3 achieves a specific strength that is more than 20 % higher compared to the reference.

Another positive effect of reducing density is the decreasing thermal conductivity. Comparing the samples without and soley with expanded glass reveals a density reduction of 62 %, which causes a decrease in thermal conductivity from 0.78 W/(m·K) to 0.16 W/(m·K). This corresponds to a reduction of 79 %.

At several Euro per kilogram, the price of pure resin is significantly higher than that of Poraver®. In addition, syntactic foams with expanded glass show good strength even with a lower resin content. Therefore, the material costs for a resin-bonded part can be reduced by using Poraver®. Even in comparison to comparable fillers for the production of syntactic foams, such as hollow glass microspheres, Poraver® is a more cost-effective alternative.

Versatility in application

Due to the high temperature resistance of the expanded glass, there is also the possibility of infiltration with thermoplastics and molten metals such as aluminium or zinc. Due to the large selection of matrix materials, a multitude of application areas and forms are possible. Walls of liquid heat accumulators, car body components and support cores can be cited as examples.


Do you have any questions? We are happy to answer them - contact us at any time!