Microwave Curing of Silicone Elastomers and Foams for Energy Savings

Jul 23, 2009 - 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 t...
0 downloads 10 Views 497KB Size
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