In practice, fibrous materials, such as glass wool, rock wool and
natural plant fibers, and highly porous materials, such as polymer,
aluminum, glass and cement foams, are often used as sound
absorbing and insulting materials. However, glass and rock wools
are sensitive to moisture and harmful to health, while natural plant
fibers and polymer foams are less fire-resistant, thus limiting their
application as sound absorbing and insulting materials. Aluminum
foams are expensive, and their sound reduction index is small at
low frequencies [6]. The manufacturing of glass foams and Portland
cement at high temperatures consumes a significant amount
of energy, and leads to the emission of huge amounts of carbon
dioxide, which is the main cause of the greenhouse effect [7,8].
Therefore, it is necessary to develop an inexpensive, fire-resistant,
energy-saving and environmentally benign sound absorbing and
insulting material to replace these existing ones.