SPEAKER INTERVIEW
Cristina Saiz-Arroyo, Manager New Products and R&D, Cellmat Technologies
Dr. Saiz-Arroyo graduated in Physics and received her PhD at the University of Valladolid, Spain. She has been working in the field of polymeric foams for more than 15 years. During these years she has been focused on the development and optimization of foaming processes and formulations for the production of advanced polymeric foams. Currently, she works as Manager of New Products and R&D in CellMat Technologies SL, which is a spin-off company of the CellMat Laboratory of the University of Valladolid. Since then, she has worked on more than 100 projects for companies involved in the plastic-producing and transformer sector. She will be speaking at Foam Expo North America and Adhesives & Bonding Expo on June 26.
Reducing weight is essential in automotive and construction applications. Why is this requirement so fundamental to these specific end-users?
In the specific case of the automotive industry, there is a direct translation between weight and fuel or energy consumption. Regulations and the interest in becoming more sustainable and reducing the CO2 footprint in the whole value chain clearly motivate the need for lightweighting.
In the automotive industry, it is clear, that the lighter, the better. Reducing the weight of a motor vehicle by 10 % reduces the raw material consumption but also reduces fuel consumption by 6 to 8%. The weight of a vehicle is its most significant tractive force and 75 % of fuel consumption depends on it. Additionally, in the last years, the average weight of the cars has overall increased due to the size increment triggered by the boom of SUV vehicles. Counteracting by introducing lighter materials or technologies aimed at reducing the weight of specific parts has become a paramount need.
In the case of construction applications, they also face challenges connected with the reduction of CO2 footprint. Reducing the consumption of raw materials is driven in this sector by two mainstreams: the reduction of density of the different solutions and therefore the generation of lighter products and the introduction of PCR resins in significant percentages to reduce the amount of virgin material included in the formulations. The main challenge to being able to create lighter products in this sector is being able to create products with reduced thermal conductivities so a product with a reduced thickness can reach a similar level of insulation and at the same time keep enough mechanical performance for a lower density.
To what extent has sustainability shaped the adoption of lightweight solutions in the automotive market?
During the last few years, more and more stringent regulations are hitting the automotive sector. Europe, set a target of 95 g of CO2 emissions per km for vehicles in 2021 aiming to reduce this value to 70 g/km by 2025. It is followed by the United States which has set a target of 89 g/km for 2025. Every 100 kg removed from a motor vehicle reduces CO2 emissions by 9 g per km, therefore, is clear that producing lighter cars undoubtedly helps to boost sustainability. Therefore, is clear that lightweighting via different strategies including foaming is key to increasing the sustainability of traditional gasoline-powered cars but also EVs. The latter do not emit CO2 while driving, contributing to reducing its carbon footprint, however, lighter solutions are clearly welcome since they contribute to battery duration and performance.
The replacement of heavy materials (metals) by lighter ones (metals or composites for example) has contributed historically to reducing the weight of vehicles. However, there are still many plastic-based parts whose weight can be further reduced by adopting other approaches like foaming.
Why does weight reduction often lead to the loss of essential foam properties, such as stiffness and impact resistance, and what kind of consequences does it cause?
The introduction of a gas phase is typically accompanied by a reduction of stiffness and impact resistance. The rate at which mechanical properties are lost depends on density, typically, the higher the density reduction, the higher the loss in properties. Additionally, it is well known that density reduction does not affect every property in the same way. For example, the rate of reduction of stiffness with density is less pronounced than that suffered by impact resistance. In high-density materials (relative density higher than 0.6) for example, the reduction of stiffness is almost proportional to the reduction of density, however, the reduction of impact resistance is proportional to the reduction of density elevated to the power of 3 to 4. Such a strong reduction in impact resistance is in many cases accompanied by a change in the failure mode of the product. This effect is known as the ductile-brittle transition.
In this scenario, it is clear that introducing additional levels of weight reduction (i.e., density reduction), will not have a strong impact on the stiffness of the part but will cause a drastic reduction in the energy absorbed by the material and in the worst case how it breaks in an impact event.
What tools and techniques are presently accessible to facilitate the maintenance of these essential properties?
The main tool to arrest the dramatic loss of properties is mainly working on an approach focused on the smart design of the formulations to be employed to create lightweight solutions.
The properties of a foam (at a given density) depend on two main factors, the properties of the solid formulation and the morphology of the cellular structure. Taking this into consideration, it is clear, that the design of formulations can not solely focus on the properties and characteristics of the solid formulation but also on their capability to create a cellular structure able to maximize the properties of the foams at this density. Therefore, a new concept, known as foamability (the ability of the formulation to create a foam with an optimized cellular structure), shall be introduced in the formulation design.
Figuring out formulations fulfilling the technical criteria (this is having adequate mechanical or even thermal properties) is no longer enough when speaking about lightweighting. Foamability will in the first place dictate if the formula will be able to reach the desired density (i.e., expansion ratio) but also if it would provide a good quality cellular structure (fine and homogeneous closed cells in the case for example of high-density products) or a poor one (heterogeneous structures that could be even interconnected).
The importance of foamability reflects on the influence of the cellular structure in the rate at which properties are reduced when density is reduced. A good quality cellular structure can contribute to minimizing the rate at which properties are lost. However, a poor cellular structure can even hinder the use of the lightweighted solution.
In what way does CellMat Technologies support companies to develop advanced formulations capable of achieving large weight reduction levels while still maintaining excellent levels of stiffness and impact resistance?
During the last few years, CellMat Technologies has worked strongly on the design of formulations aimed at foaming applications for different industries, including the automotive and building industries. By using a combination of foamability prediction, designing of optimized formulations, modeling of properties, and prototype manufacturing and validation we have succeeded in the development of solutions that can display a better performance with the same density or even mimic the properties of current solutions but with a higher density reduction.
