5 Microwave Curing of Silicone Elastomers and Foams for Energy Savings C. L. LEE
Downloaded by CORNELL UNIV on September 22, 2016 | http://pubs.acs.org Publication Date: August 29, 1979 | doi: 10.1021/bk-1979-0107.ch005
Research Department, Dow Corning Corp., Midland, MI 48640
When dielectric materials are heated by microwave, the heat generated, P, is given by the following equation (1) 2
-6
Ρ = 0.555 f ε E'tan δ x 10 Where f ε Ε' tan δ
= frequency = field strength = dielectric constant = loss tangent
For a given f and ε , the heating efficiency is directly propor tional to E' and tan δ. The product of these two parameters is called the loss index, ε". Loss index of 0.2 or more results in good heatability; 0.08-0.2, fairly good heatability; 0.01-0.08, poor heatability; and under 0.01 there is l i t t l e or no response (2). The loss index of silicone elastomers made from polydimethylsiloxane, generally speaking, is low due to their low values of dielectric constant and loss tangent. The dielectric constant of polydimethylsiloxane is almost independent of the frequency, where as the tan δ is highly dependent on the frequency in the micro wave region (3,4). At 3 x 10 Hz, a 1000 cs polydimethylsiloxane fluid has a tan δ of about 0.0096 and a dielectric constant of 2.76. This gives a loss index of 0.0264, which puts polydimethyl siloxane in the poor heatability category. One can, however, increase the loss index of silicone poly mers by increasing either E' or tan δ of the material. This can be done in two ways, i . e . , 9
A. Changing the s t r u c t u r e o f the s i l i c o n e polymer. B. Introduce an a d d i t i v e , which has a high l o s s index. In the former approach, the l o s s index can be increased by changing the s u b s t i t u e n t s on s i l i c o n e . Vincent et a l (5_) r e ported that as the R group i n Me3Si0(MeRSi0) SiMe was changed from methyl to a bulky p o l a r group, the d i e l e c t r i c constant and l o s s f a c t o r increased d r a s t i c a l l y . T h i s i s shown i n Table I . x
3
0-8412-0509-4/79/47-107-045$05.00/0 © 1979 American Chemical Society
Vigo and Nowacki; Energy Conservation in Textile and Polymer Processing ACS Symposium Series; American Chemical Society: Washington, DC, 1979.
ENERGY
46
TABLE 1.
CONSERVATION
ΓΝ
TEXTILE
AND
POLYMER
PROCESSING
E f f e c t Of Chemical Composition On The D i e l e c t r i c Constant Ε and Tan δ Of Me SiO(MeRSiO) SiMe > 1
( a
3
E R
100 8
9
Downloaded by CORNELL UNIV on September 22, 2016 | http://pubs.acs.org Publication Date: August 29, 1979 | doi: 10.1021/bk-1979-0107.ch005
3
2
3
2
2
2
6
3
f
Hz
tan δ 1,000
2.38 2.54 2.76 3.03 3.18 6.84 6.84 19.28
-n-C Hi7 -η-^Η CH 0HC1(CH ) CF (CH ) ρ-Ν0 -0 Ηι»3
x
1.38 2.54 2.76 3.04 3.18 6.84 6.84 18.85
Hz
100
1,000
Hz
Hz
