Materials Science and Engineering, A 111 ( 1989) 217-225 217 Scanning Electron Microscopy Observations of Insulation Cork Agglomerates H. PEREIRA Departamento de Engenharia Florestal, Instituto Superior de Agronomia, 1399Lisboa (Portugal) E. FERREIRA INFAL - lndfstria de Fabricacdo de Aglomerados Sarl, 2870 Monti]o (Portugal) (Received January 4, 1988; in revised form October 19, 1988) Abstract Observations by scanning electron microscopy were made of insulation cork agglomerates and of cork raw material The insulation cork agglomer- ates are agglomerates of granules of cork from the cork-oak tree (Quercus suber), self-bonded and expanded by autoclave steaming at approximately 300 °C and 40 kPa. In this process, the cork cells expand by unfolding the cell wall corrugations and by stretching the cell walls (concurrently decreasing the cell wall thickness). In the junctions between granules, the cells are compressed against each other and collapsed," the region of cell collapse is restricted to a limited number of cell layers at the boundary between the granules. The cell wall material is thermochemically degraded and a weight loss of approximately 30% of the cork material is observed in the production of these insulation agglomerates. I. Introduction Insulation cork agglomerates are manu- factured by the high temperature compression of granules of cork from Quercus suber. Particle diameters are usually in the range 0.5-1.5 cm. The process involves the direct steaming of the cork particles at approximately 300°C and 40 kPa without the use of any adhesive. Under these conditions, the cork granules expand and self-bond to each other. Autoclaves with hydraul- ic moving bottoms (or tops) are used and some compression is applied to the cork granules before steaming. The final product density may be varied by the extent of this precompression. Insulation cork agglomerates are known as pure expanded agglomerates since no foreign material is added to the cork. They are also known as black agglomerates because of their dark colour. They are produced with the lowest quality corks: mostly with virgin cork, the first- generation cork, which is rough, with deep cracks and unsuitable for other uses, and also with low quality reproduction cork as well as with cork wastes and remnants from industrial processing. The cork agglomerates obtained in this way have some remarkable properties: they are light, have a low thermal conductivity and a low per- meability to water, and are good sound insulators. Because they are chemically stable, they are resis- tant to microbial degradation and to attack by rodents, and are very durable. Table 1 sum- marizes some of the properties of insulation cork agglomerates [1, 2]. Insulation cork agglomerates are used in build- ing and industrial plants in the form of boards, pipe coverings and blocks, for thermal insulators and as sound and vibrational barriers. Utilization in interior decoration for wall or ceiling surfacing is also common. However, it is in cold storage that insulation corkboard presents outstanding advantages in relation to other insulating TABLE 1 Some propertiesofinsulation cork agglomerates [1, 2] Property Range of values Density Working temperatures Thermal conductivity (20 °c) Specific heat (20 °C) Thermal diffusivity (20 °C) Permeability to steam lO0-130kgm 3 - 180to +llO°C 0.035kcalm- i h -I °C t 0.4-0.5 kcal kg- i °C i 0.00050-0.00073 m 2 h i 0.002-0.006gm ~ h i(mmHg) i 0921-5093/89/$3.50 © Elsevier Sequoia/Printed in The Netherlands