# Determination of Acceleration Factor

Changes in the QS-value of the different sealants within set 2 with natural and artificial weathering carried out according to the conditions indicated in Table 7 are indicated in Table 8 (and shown in Fig. 9). Because exposure occurred only under dynamic conditions (with forced movement), the QS-value was determined at three points along the central axis of the test specimen, corre­sponding to movement amplitudes of 1.5%, 15%, and 25%. The MS-1 product showed adhesion failure at the 25 % extension/compression amplitude in the XWOM and SWOM exposures. The process of calculating the acceleration fac­tor between accelerated weathering and natural outdoor weathering for each sealant and the specific artificial light source is indicated below using the MS-2 product as an example (see also Fig. 10).

• The QS-values of the specific product are converted to a three­dimensional diagram as shown in Fig. 6.

• The time required in order to reach a specific QS-value was read from each of the diagrams (natural and three accelerated weathering exposures).

TABLE 9—Accelerating factors of each sealant.

 Light Source SR-2 MS-2 MS-1 PU-2 PU-1 XWOM 11.4 11.4 18.0 9.5 SWOM 16.2 18.3 16.4 25.3 UV 4.7 3.0 6.7 2.7

• The time period derived for outdoor exposure (to reach a specific QS – value) was divided by the corresponding time periods for each light source as shown in Eq 3.

• The average acceleration factor for each artificial weathering condition was calculated by repeating the above-described process for the differ­ent extension/compression amplitudes and then averaging the results

K = t[outdoor]/t[light source] (3)

where:

K = accelerated factor/ratio,

t[outdoor] = time period required in order to reach a specific QS-value in outdoor exposure, and

t[light source] = time period required in order to reach a specific QS-value in accelerated exposure.

The acceleration factors for the different light sources versus natural weath­ering are given in Table 9, and the irradiation time of each accelerated light source corresponding to one year of outdoor exposure is given in Table 10 as calculated according to Eq 4. As the silicone sealant product shows no degrada­tion, no numerical acceleration factor can be determined. The other products show acceleration factors, approximately over 10 for XWOM and SWOM expo­sures and below 5 for UV exposure.

Irradiation time equivalent to one year of outdoor exposure

= 24 hours x 365 days/accelerated ratio (4)

TABLE 10—Irradiation time corresponding to one year.

 Sealant XWOM SWOM UV SR-2 MS-2 750 550 1850 MS-1 750 500 2900 PU-2 500 550 1300 PU-1 900 350 3250

Unit: hours.