Page 39 - Plastics News October 2016

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Effective stabilization for state-of-the-art hybrid polymer sealants

EVERLIGHT CHEMICAL INDUSTRIAL CORPORATION
Technical Service Dept. Specialty Chemicals BU

Hybrid polymer, especially Silyl-modified polyether (known (RO.) Those alkyoxy radicals will react with polymers and
as STPE polymers) and silyl-modified polyurethanes (known start the chain oxidation reaction which cause fragments
as SPUR polymers) are the modern hybrid sealants (SMP) and decrease the molecular weight .We can observe the
which can be used in wide ranges of applications, such as dropping viscosity (16000=>740 c.p.s). Besides, thermal-
construction and transportations. Combining the strength oxidation degradation will also generate free radical
of polyether and polyurethanes with the weathering resulting more complicated degradation which cause
resistance of silicones make these hybrid sealant as polymers turn yellow quickly. (Yi form 1.49 =>87.8).
high performance. But these hybrid sealants also shows
some disadvantages, for examples: yellowing, chalking, (Figure 2)
cracking, after exposing under sunlight in outdoors or STPE resin discoloration after UV and Heat exposure test
high temperature conditions after several months. So
how to improve the weatherability of SMP sealants, we Type of Additives Examples Ratio
found out better weathering resistance results by adding Resin Polymer STPE resin 20~35%
Eversorb. HP1 Plasticizers Phthalates, PPG 20~30%
Fillers Fumed Silica ; Calcium 30~50%
More than 65% of SMP sealants choose STPE polymer as Carbonate
their basic resin. The leading STPE polymer suppliers Stabilizers UV and Heat stabilizers <2%
are Kaneka from Japan and Wacker form Germany. The (Eversorb HP1)
structure of an STPE polymer consists of a polyether Catalysts U220H (Sn(IV)) <0.5%
backbone and silane terminal functionality (Figure 1). Moisture Scavengers Vinyl silanes <1%
Adhesion Promoters Amino/epoxysilanes <0.5%
Condition Yellow Index (Yi) Viscosity (c.p.s at 20oC TiO2; Carbon Black <10%
Pigment
0 hr 240 hrs 0 hr 240 hrs

A 5oC(UV lamp 340nm) 1.47 6.35 16000 740

B 105oC (Oven) 1.49 87.8 16000 24540

(table1)

(Figure 1) (table 2)

Although STPE polymer do not contain urethane bond or 1. QUV exposure test for transparent STPE sealant
aromatic groups, light or heat will still cause photo and
thermal degradation. The test results of UV exposure 1 Test Sample : 2mm STPE sealant plate and Dumb
test (340nm,0.89 W/m2/nm) and oven test (105oC) for bell (ASTM D412 ; Die C)
240 hours both shows the polymer degradation and
result in yellowness. (Figure 2) and a dramatic change of 2. Measure unit: Yellowness index (Yi) / Tensile
viscosity (table1). This results show photo degradation strength and Elongation retention (%)
will break ether chain and generate free alkoxy radicals
3. Criteria: ASTM G154-1(340nm UVA lamp) ;

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

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