Poly(methyl methacrylate) vs. Polycarbonate

Attribute	Poly(methyl methacrylate)	Polycarbonate
Chemical Formula	C5H8O2	(C16H14O3)n
Common Name	Acrylic or PMMA	PC
Transparency	High transparency	High transparency
Impact Resistance	Brittle	High impact resistance
Tensile Strength	Medium	High
Flexibility	Rigid	Flexible
Heat Resistance	Good	Good
Chemical Resistance	Resistant to many chemicals	Resistant to many chemicals
UV Resistance	Low	High
Applications	Signage, displays, lenses	Automotive parts, safety glasses

Introduction

Poly(methyl methacrylate) (PMMA) and polycarbonate (PC) are two widely used thermoplastic materials with distinct attributes and applications. Understanding the differences between these materials is crucial for selecting the appropriate material for specific projects. In this article, we will compare the attributes of PMMA and PC, including their physical properties, chemical resistance, optical clarity, impact resistance, and applications.

Physical Properties

PMMA, also known as acrylic, is a transparent thermoplastic with excellent optical clarity. It has a high glass transition temperature (Tg) of around 105°C, making it suitable for applications requiring dimensional stability at elevated temperatures. PMMA has a relatively low melting point of approximately 160°C, which allows for easy processing through various techniques such as injection molding and extrusion.

On the other hand, PC is a transparent amorphous thermoplastic with a higher Tg of about 145°C. It has a higher melting point of around 240°C, making it more heat resistant than PMMA. PC also exhibits excellent dimensional stability, even at elevated temperatures, which makes it suitable for applications requiring high-temperature resistance.

Both PMMA and PC have good electrical insulation properties, but PC has a higher impact strength compared to PMMA. PC is known for its exceptional toughness, making it more resistant to impact and cracking. PMMA, although not as impact resistant as PC, still possesses good mechanical strength and can withstand moderate impacts.

Chemical Resistance

When it comes to chemical resistance, PMMA and PC have different characteristics. PMMA is resistant to many common chemicals, including alcohols, dilute acids, and alkalis. However, it is susceptible to solvents such as acetone and chloroform, which can cause crazing or cracking. PMMA is also sensitive to UV radiation, leading to yellowing and degradation over time.

On the other hand, PC exhibits excellent chemical resistance to a wide range of chemicals, including many solvents and acids. It is more resistant to UV radiation compared to PMMA, making it suitable for outdoor applications where prolonged exposure to sunlight is expected. PC's superior chemical resistance and UV stability make it a preferred choice for applications requiring long-term durability.

Optical Clarity

Both PMMA and PC are known for their optical clarity, but there are some differences between the two. PMMA has exceptional transparency, with a light transmission of around 92%. It has a refractive index of approximately 1.49, which is close to that of glass, resulting in minimal light scattering and excellent optical properties.

PC also offers high optical clarity, with a light transmission of about 88%. However, PC has a higher refractive index of around 1.59, which can lead to more light scattering compared to PMMA. This difference in refractive index can be a consideration in applications where optical quality is critical, such as lenses or display panels.

Impact Resistance

As mentioned earlier, PC is known for its exceptional impact resistance. It is virtually unbreakable, even at low temperatures, due to its high toughness and ductility. PC can withstand significant impacts without shattering or cracking, making it an ideal choice for applications requiring impact resistance, such as safety glasses, protective shields, and automotive components.

While PMMA is not as impact resistant as PC, it still possesses good mechanical strength and can withstand moderate impacts. PMMA is often used as a lightweight alternative to glass, where impact resistance is not the primary requirement. It is commonly used in applications such as signage, lighting fixtures, and display cases.

Applications

PMMA and PC find applications in various industries due to their unique attributes. PMMA's excellent optical clarity and weather resistance make it suitable for outdoor signage, architectural glazing, and lighting fixtures. It is also commonly used in the automotive industry for headlight lenses and interior trim components.

PC's superior impact resistance and high-temperature stability make it ideal for applications requiring durability and safety. It is widely used in the automotive industry for windshields, safety glasses, and interior components. PC is also used in electronics, such as smartphone screens and computer housings, where impact resistance and optical clarity are essential.

In summary, PMMA and PC have distinct attributes that make them suitable for different applications. PMMA offers excellent optical clarity, good mechanical strength, and chemical resistance to many common chemicals. PC, on the other hand, provides superior impact resistance, high-temperature stability, and excellent chemical resistance to a wide range of chemicals. Understanding these differences allows engineers and designers to select the most appropriate material for their specific project requirements.