Effective Stabilisation for State-of-the-Art hybrid Polymer Sealants

Hybrid polymer, especially Silyl-modified polyether (known as STPE polymers) and silyl-modified polyurethanes (known as SPUR polymers) are the modern hybrid sealants (SMP) which can be used for wide ranges of applications, such as construction and transportations. Combining the strength of polyether and polyurethanes with the weathering resistance of silicones make this hybrid sealant as high performance. But these hybrid sealants also shows some disadvantages, for examples: yellowing, chalking, cracking, after exposing under sunlight in outdoors or high-temperature conditions after several months. So how to improve the wearability of SMP sealants, we found out better weathering resistance results by adding Eversorb. HP1

More than 65 percent of SMP sealants choose STPE polymer as their basic resin. The leading STPE polymer suppliers are Kaneka from Japan and Wacker from Germany. The structure of an STPE polymer consists of a polyether backbone and silane terminal functionality.

Although STPE polymer does not contain urethane bond or aromatic groups, light or heat will still cause photo and thermal degradation. The test results of UV exposure test (340nm,0.89 W/m2/nm) and oven test (105?) for 240 hours both shows the polymer degradation and result in yellowness. (Figure 2) and a dramatic change of viscosity (table1). These results show photodegradation will break either chain and generate free alkoxy radicals (RO.) Those alkyoxy radicals will react with polymers and start the chain oxidation reaction which causes fragments and decrease the molecular weight.We can observe the dropping viscosity (16000=>740 c.p.s). Besides, thermal oxidation degradation will also generate free radical resulting more complicated degradation which causes polymers turn yellow quickly. (Yi from 1.49 =>87.8).

1. QUV exposure test for transparent STPE sealant

1. Test Sample: 2mm STPE sealant plate and Dumb bell (ASTM D412; Die C)

2. Measure unit: Yellowness index (Yi) / Tensile strength and Elongation retention (%)

3. Criteria: ASTM G154-1(340nm UVA lamp);

4. Test period: 1000 hrs.; Temperature: 50 °C

STPE transparent sealant without UV stabilisation in QUV test will turn yellow and decompose very quickly less than 100 hours. By adding Eversorb HP1 2,4% can well protect STPE sealant not to be decomposed and keep colour retention.

2. QUV exposure test result for grey STPE sealant

1. Test Sample: 2mm grey STPE sealant plate

2. Measure Unit: Delta color difference (?E) /Tensile strength and Elongation retention (%)

3. Criteria: ASTM G154-1(340nm UVA lamp);

4. Test period: 1000 hrs.; Temperature: 50 °C

Adding 1phr,2phr Ev.HP1 in STPE grey sealant is slightly different in colour difference. Besides, adding TiO2, carbon black and other filler can also decrease the impact of yellowness issue and adding Ev.HP1 can help to maintain tensile strength and elongation retention after QUV exposure test.

Conclusions:

1. Why hybrid polymer sealant need Eversorb for stabilisation?

Using UV light stabilisation to improve the hybrid polymer sealant further in UV stability and adhesion after a long-time outdoors exposure is necessary. Everlight Chemical provide solutions of Eversorb® HP1 to reduce polymer degradation such as yellowing, cracking, losing mechanical and elastic properties.

2. What are the advantages of Eversorb® HP1

Eversorb® HP1 is a high-performance UV stabiliser providing a long-term UV protection for STPE polymers, especially those high-performance sealants for construction, automotive and other outdoor applications. Unlike other powder additives, its liquid form can homogeneously incorporate in resin system which means you won’t need any heat up a process for incorporation and hardly concern the migration issue.

3. Our recommendation

The recommended dosage of Eversorb HP1 is 0.5~3% based on resin solid. Incorporating Eversorb HP1 in resin prior to catalyst is recommended as another catalyst might interact or interfere the system.

Article By: Everlight Chemical Industrial Corporation, Technical Service Dept. Specialty Chemicals BU