Formulating High Weatherability Sealants: Possibilities and Challenges

ABSTRACT: Customers challenge sealant formulators to develop high weatherability construction sealants with ever-higher performance. This paper will discuss some of the factors that influence weatherability and durability of sealants, such as binder, pigments, stabilizers, and catalysts. One-component polyurethane and modified silicone sealants will be evaluated. Raw material influences need to be carefully tested and optimized in order to develop high weatherability sealants. Taking these factors into consideration, it is possible to formulate high weatherability sealants that meet customers’ demands. These demands are expected to increase in the future.

KEYWORDS: construction sealants, polyurethane, modified silicone, weatherability, raw material influences

Introduction

Customers demand construction sealants with constantly increasing durability and weathering perfor­mance. Formulators have to respond to requests for outdoor weathering performances of 20 years and more. The challenge in meeting these requirements lies not only in the actual development of such sealants but also in finding reliable test methods to evaluate the different formulas and to estimate service life.

Xenon arc, fluorescent UV, carbon arc, and metal halide sources are commonly used to determine the accelerated weathering performance of sealants, adhesives, and other materials [1,2]. However, the prac­tical value of accelerated weathering data is often limited to relative comparisons because such data applies only to specific formulas and test conditions; therefore, it seems to be difficult to arrive at reliable correlations between accelerated weathering data and outdoor weathering results [1-3]. Formulators will therefore often have to find their own methods to gauge outdoor performance.

In this paper we will consider some of the influences that determine durability and weatherability, such as binders, pigments, plasticizers, catalysts, and additives. Examples based on polyurethane and modified silicone [4] sealants will be discussed from a formulator’s point of view.