Kevin Lewis examines lightweight foam formulations for advanced applications in the transportation sector
The versatile properties of modern silicone elastomers are essential in our digital world and increasingly electrified mobility. Advanced silicone products with technology-enabling properties are an important ingredient for future products and developments. Lightweight silicone products are a logical next step to conquer the increasing need for higher efficiency in the transportation sector.
Upon becoming commercially viable in the 1940s, silicones have developed into a versatile class of polymers that form the basis of many products spanning a wide variety of consumer and industrial applications. The inherent properties of this class of polymer enable a design space where viscosity, rheology and cure profile (if applicable) can be tailored to suit processing, and hardness along with elements of physical strength such as tensile, tear, and elongation can be adjusted to enable longevity in the end-use application. Though inherently insulative, silicones can be formulated into thermally and/or electrically conductive compositions allowing them to serve as a key material in technologically demanding applications. The ability of silicone to offer protection from the environment or relatively harsh operating conditions is enabled, and sets them apart from other chemistries, by their inherent chemical stability and wide range of temperature use – typically -55 to 200°C and can be further broadened with modification. The combination of customisability and inherent properties can enable silicones to be a better cost-in-use solution relative to other chemistry sets due to longevity and processing advantages in the application.
Where Can They Be Used?
As mentioned above, silicones find utility in many applications. Some, such as caulking compounds, “gasket-maker in a tube” and O-rings are familiar to a common end user. Being ubiquitous, one often encounters silicone-based products, perhaps unwittingly, in numerous other applications. For example, syringe needles are often lubricated with a thin layer of silicone to lessen the insertion force and the pain or skin trauma involved with receiving a vaccination. For textiles, items such as bath towels are often treated with a fabric softener based upon silicone to impart smoothness and richness. In more industrial oriented applications, such as the powertrain control module of a vehicle, a silicone product is often used in the form of a conformal coating, gel or thermally conductive potting compound to provide protection by preventing moisture ingress, dampening vibration or transferring away heat to prevent hotspots and thermal failures. Outdoor LED displays used for advertising or at sporting events often incorporate silicone to protect electrical components to ensure the screen can operate over a wide range of outdoor temperatures and offer protection against moisture.
As society moves toward an increasingly environmentally conscious future, particularly regarding transportation, silicone-based products present an opportunity to provide protection and do so in a lightweight format. Various lightweighting methods can be employed to lower the inherent density of silicone.
These may include “whipping air” into the formulation, incorporating low-density fillers, or creating a self-blowing formulation; all of which result in cured-in-place voids or bubbles comprising a type of silicone foam.
Unbeknownst to many, passengers embarking on tube trains are sitting on cushions made from a silicone foam and those on aeroplanes are surrounded by a fuselage containing a layer of silicone foam. The products used in these applications are engineered specifically to result in a high-quality silicone foam that is a resilient flexible solid that is cut or carved to shape. And most important for these applications, the final product is flame-retardant, self extinguishes and generates only traces of white smoke. With the increasing development and adoption of electric vehicles, manufacturers and governing bodies will seek technologies that enhance efficiency of the automobiles and safety of the passengers.
A Flexible Solution
With the goal of streamlining manufacturing and enhancing the safety and efficiency of vehicles in the transportation sector, CHT USA has introduced a liquid silicone formulation that cures to form a solid foam. Designing the formulation to be modest in viscosity allows it to flow around complex parts and shapes. Upon mixing volumetrically in a 1:1 ratio, the curing process begins immediately where a number of processes take place: the foaming reaction; viscosity build to stabilise foam cells; and gelation to lock the structure in place. The product is designed with speed of manufacture in mind; the initial cure for building structure and volume is complete and the product is “dry to touch” after approximately 10 minutes. On average, dispensing two litres of liquid results in approximately five litres of cured silicone foam that is flame-retardant and self-bonding to many surfaces.
Kevin lewis, PhD is reasearch &development director at CHT, USA