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HINA R&P TECHNOLOGY AND EQUIPMENT

pieces into standard specimens. 2.1.1 Density and expansion ratio of foamed
Table 5 Experimental formula and process parameters silicone rubber with physical foaming agent
using hollow glass microspheres added
Serial Fill and add Process temperature / ℃ Curing time
number proportion (in minutes) Through calculation, the density and expansion ratio of
B1 5% 130 10 foamed silicone rubber prepared with different proportions of
B2 6% 130 10
B3 8% 130 10 physical foaming aids under pressurized and unpressurized
conditions were obtained. As shown in Figure 1, with the
1.3 Testing and characterization increase of the content of physical foaming aids, the density of
(1) Testing of foam material density and expansion ratio: foamed silicone rubber gradually decreases, and the expansion
Cut the foamed silicone into cuboids, weigh its mass, measure ratio gradually increases. When the mass fraction of physical
the side length, calculate the volume, and obtain the density. foaming aids reaches 2% under unpressurized conditions,
Then compare it with the parameters of unfoamed silicone to the density of foamed silicone rubber is 0.4 g/cm3, and the
obtain the expansion ratio, which is calculated according to expansion ratio is 2.73 times; when the mass fraction reaches
formula 1 or formula 2. 4%, the density of foamed silicone rubber is 0.27 g/cm ,
3
Foaming ratio=volume after foaming / original volume (1) and the expansion ratio is 4.04 times, making it a medium-
N=ρ 1 /ρ 2 (2) expansion foam material. Pressure has a significant impact on
In the formula, N represents the foaming ratio, ρ1 denotes the foaming density and expansion ratio during the foaming
the initial apparent density of silica gel, and ρ2 signifies the process. The density of foamed silicone rubber obtained under
apparent density of foamed silica gel. unpressurized conditions is lower than that obtained under
(2) Mechanical property testing: Cut the foamed silicone pressurized conditions, and the expansion ratio of foamed
rubber into standard dumbbell-shaped tensile specimens. The silicone rubber obtained under unpressurized conditions
tensile strength is tested using dumbbell-shaped specimens is higher than that obtained under pressurized conditions,
with a testing speed of 100 mm/min, a gauge length of 25 indicating that reducing pressure can yield better foaming
mm, and a testing environment temperature of 23±2 ℃ and materials.
humidity of 50±5%. The tensile properties of the specimens are 2.1.2 Density and expansion ratio of foamed
tested using a tensile machine that complies with ISO5893 and silicone rubber with sodium bicarbonate as
has a force measurement accuracy of Level 2. The accuracy foaming agent
of the extensometer used in the testing machine is Level D Sodium bicarbonate is an endothermic foaming agent that
for Type I, Type II, and Type IA dumbbell-shaped specimens, decomposes endothermically at a temperature ranging from
and Type A ring specimens; Level E for Type III and Type 60 to 150 ℃, producing gases CO 2 and H 2 O. The chemical
IV dumbbell-shaped specimens, and Type B specimens. The equation for its thermal decomposition is shown in Equation 3.
testing machine should be capable of operating at a minimum 2NaHCO 3 ＝ Na 2 CO 3 +H 2 O+CO 2 ↑ (3)
of 100 mm/min±10 mm/min, 200 mm/min±20 mm/min, and The influence of the mass fraction of sodium bicarbonate,
500 mm/min±50 mm/min. a foaming aid, on the density and foaming ratio of foamed
(3) Observing the morphology of foamed silicone silicone rubber is shown in Figure 2. As can be seen from
rubber using an electron microscope: Take a cross-section Figure 2, with the increase in the proportion of sodium
of the foamed solid silicone rubber and observe it under a bicarbonate added as a foaming aid, the density of foamed
microscope.
silicone rubber decreases, and the foaming ratio increases.
When 2% sodium bicarbonate is added, the density of foamed
2 Results and discussion silicone rubber is 0.67 g/cm , and when 3% sodium bicarbonate
3
2.1 Density and expansion ratio of foamed is added, the density is 0.66 g/cm . The foaming effects of
3
materials adding 3% and 2% sodium bicarbonate are not significantly

·44· Vol.51，No.12