PC and TPU: the science behind phone case materials

Polycarbonate (PC) and Thermoplastic Polyurethane (TPU) are two key materials in phone case production, each with distinct properties. PC offers rigidity, clarity, and strong impact resistance, making it ideal for protective, clear cases. TPU, known for its flexibility and shock absorption, provides a softer, grippier texture. We've explored the science behind these materials to help you make an informed choice.

Polycarbonate (PC) is a strong, transparent plastic composed of large molecules called polymers. Its unique atomic structure grants it exceptional properties, including:

• High strength-to-weight ratio: PC is remarkably durable for its lightweight composition. It can withstand significant impact forces without breaking or deforming, making it ideal for applications requiring high mechanical strength.
• Heat resistance: PC can resist elevated temperatures without softening or deforming, making it suitable for use in environments with extreme heat conditions. It can withstand temperatures up to 130°C (266°F) without losing its mechanical properties.
• Flame retardancy: PC is inherently resistant to combustion, making it a safe material for applications requiring fire safety. It is classified as self-extinguishing, meaning it will stop burning on its own once the ignition source is removed. This property is particularly valuable in industries such as electronics, automotive, and construction, where fire safety is a critical concern.
• Transparency: PC is optically clear, allowing for the creation of translucent or transparent products. Its high light transmission makes it an excellent choice for applications requiring visibility, such as lenses, windows, and lighting fixtures. PC's transparency also enables the incorporation of decorative elements or the display of underlying designs.

PC is a popular choice for phone case manufacturers due to its:

• Durability: PC cases can effectively protect phones from drops, bumps, and scratches.
• Precision molding: PC allows for the creation of cases with precise fits and intricate details, ensuring that the case fits snugly around the phone and provides optimal protection.
• Clarity: PC's transparency enables the display of phone designs or the addition of decorative elements. This allows users to showcase the phone's aesthetic appeal or personalize their device with unique designs. PC cases can also be made with transparent backs, allowing users to admire the phone's design while still providing protection.
• Scratch resistance: PC is more resistant to scratches than many other plastics, maintaining a pristine appearance over time.

While PC offers numerous advantages, it also has some drawbacks:

• Rigidity: PC can be less flexible than softer materials, potentially affecting shock absorption. For example, while PC cases can provide excellent protection against drops and bumps, they may not be as effective at absorbing the impact of a fall from a great height or a direct hit to a vulnerable area of the phone. In contrast, softer materials like silicone or TPU can better absorb shock energy, reducing the risk of damage to the phone's internal components.
• Yellowing: Some types of PC may yellow over time when exposed to ultraviolet (UV) radiation. This is particularly noticeable in cases that are frequently left outdoors or exposed to direct sunlight. However, manufacturers often incorporate UV stabilizers into PC to mitigate this issue.
• Cost: PC can be more expensive than other plastics, potentially increasing the overall cost of a product. This is due to the higher cost of the raw materials used to produce PC, as well as the additional processing steps required to create products with the desired properties.
• Susceptibility to cracking: While PC is tough, it can crack under extreme stress, especially when subjected to sharp impacts or sudden temperature changes. For example, dropping a PC case onto a hard surface from a great height or exposing it to extreme temperature fluctuations can increase the risk of cracking. While PC can withstand a certain amount of stress, it is not indestructible, and it is important to handle it with care to avoid damage. In contrast, soft cases made from materials like silicone or soft-touch TPU offer greater flexibility. These cases provide a softer feel and better grip but may lack the precise molding and scratch resistance of PC.

TPU belongs to a family of elastic polymers that combine hard plastic and soft silicone. Chemists create TPU by reacting diisocyanates with diols, resulting in a material with a unique molecular structure. This structure gives TPU its characteristic elasticity and durability. TPU can stretch and then return to its original shape, making it both flexible and resistant to tearing. It also resists oils, greases, and abrasions, adding to its versatility. Recent studies have shown that TPU can be effectively blended with functionalized polypropylenes (PP), particularly those grafted with primary and secondary amines, to improve mechanical properties such as tensile strength and elongation. These compatibilized TPU/PP blends exhibit enhanced performance, making them suitable for applications requiring robust material synergy.

Phone case manufacturers love TPU for several reasons. Its flexibility allows the case to absorb shocks from drops, protecting your device better than rigid materials. TPU's soft texture provides a comfortable grip, reducing the chance of accidental drops. The material's elasticity makes it easy to fit the case onto your phone and remove it when needed. TPU resists yellowing and discoloration, keeping your case looking new for longer. Additionally, manufacturers can easily color TPU, offering a wide range of design options.

Despite its many advantages, TPU has some limitations. It's generally not as clear as hard plastics like PC, which can affect the aesthetics of transparent or translucent cases. TPU can feel 'sticky' or attract dust in some formulations, potentially making your phone feel less smooth in your pocket. While TPU offers good protection, it might not provide the same level of rigid defense against sharp objects as harder materials. Lastly, some users find that TPU cases can stretch over time, potentially affecting the fit of the case.

PC takes the crown for hardness. It's tough and rigid, providing solid protection against direct impacts. If you drop your phone on a sharp corner, PC will stand strong. TPU, on the other hand, is the flexibility champion. It bends and flexes, absorbing shocks and vibrations. Think of PC as armor and TPU as a cushion.

PC shines in the looks department. Its clarity allows for crystal-clear cases that show off your phone's design. Manufacturers can also easily add colors and patterns to PC. TPU offers a softer, more matte appearance. While it's not as clear as PC, TPU provides a sleek, modern look and comes in various colors.

TPU wins the grip game hands down. Its slightly soft, rubbery texture helps prevent your phone from slipping out of your hand. PC feels smoother and harder, which some users prefer, but it can be more slippery.

Both materials hold up well over time, but in different ways. PC resists scratches better, keeping its clear appearance longer. However, it can crack under extreme stress. TPU might show scratches more easily, but it's less likely to crack or break. It also resists yellowing better than some PC formulations.

PC offers excellent protection against direct impacts and scratches. It's great for defending against keys in your pocket or a fall onto a hard surface. TPU excels at absorbing shock from drops, potentially preventing internal damage to your phone. It also protects well against everyday bumps and scrapes.

PC allows for thinner, lighter cases without sacrificing protection. TPU cases often need to be slightly thicker to provide the same level of defense, but the difference is usually minimal.

Generally, PC costs more to produce than TPU. This often translates to higher prices for pure PC cases. TPU is typically cheaper to manufacture, allowing for more budget-friendly options.

Both materials can be recycled, but TPU often has an edge in biodegradability. Some TPU formulations break down faster than PC, potentially making it a more eco-friendly choice.

Hybrid cases blend the best of both worlds. The hard PC layer provides solid protection against direct impacts and scratches. It forms a tough outer shell, guarding against keys, coins, and other sharp objects in your pocket. The softer TPU layer acts as a shock absorber. It cushions your phone during drops, reducing the risk of internal damage. While these cases protect the body of your phone, pairing them with a screen protector made of tempered glass adds an extra layer of defense against cracks and scratches on your display. This combo offers comprehensive protection that neither material could achieve alone.

PC+TPU hybrids open up new design possibilities. Manufacturers can create cases with clear PC backs to show off your phone's design, while TPU bumpers provide grip and drop protection. This combination allows for slim profiles without sacrificing durability. Designers can play with color contrasts, textures, and patterns, mixing the materials for both aesthetic appeal and practical functionality.

Creating hybrid cases involves a multi-step process. First, manufacturers mold the PC and TPU components separately. They often use injection molding for PC and compression molding for TPU. Then, they combine these parts using various techniques. Some use adhesives, while others employ a process called two-shot molding. This method injects the materials into a single mold sequentially, creating a seamless bond between PC and TPU.

Phone case makers put their products through rigorous testing. Common tests are:

• Drop tests from various heights and angles
• Scratch resistance checks
• UV exposure tests to check for yellowing
• Fit and compatibility tests with phone models
• Button and port accessibility checks

Many manufacturers follow standards set by organizations like ASTM International or ISO. Some also seek military-grade certifications for extra durability assurance.

The tech industry is increasingly committed to sustainability, and case materials are no exception. While both polycarbonate (PC) and thermoplastic polyurethane (TPU) are recyclable, hybrid cases combining these materials can pose recycling challenges due to potential material incompatibility.

To address this, manufacturers are exploring ways to make hybrid cases more recyclable. This includes using compatible grades of PC and TPU and incorporating recycled materials. Additionally, research is ongoing into biodegradable alternatives that can decompose naturally.

By focusing on these areas, the tech industry can continue to make significant strides toward a more sustainable and environmentally friendly future.

Key points to consider:

• Recyclability: Both PC and TPU are recyclable, but hybrid cases can pose challenges due to material incompatibility.
• Material compatibility and recycled materials: Manufacturers are working to improve recyclability by using compatible materials and incorporating recycled content.
• Biodegradable alternatives: Research is ongoing into biodegradable options for a more sustainable future.

As phone technology evolves, we can expect case materials to keep pace, offering ever-improving protection, functionality, and sustainability. The future of phone case materials looks exciting. Researchers are exploring several avenues:

• Self-healing materials that can repair minor scratches and dents
• Advanced shock-absorbing compounds inspired by materials used in sports equipment
• Antimicrobial coatings to keep phone surfaces cleaner
• Eco-friendly bioplastics derived from renewable sources
• Smart materials that change properties in response to temperature or impact

Some companies are also looking into incorporating advanced features into case materials, such as improved heat dissipation for better phone performance or energy-harvesting capabilities to extend battery life.

PC is the go-to for clear, tough cases thanks to its high impact resistance and heat tolerance, though it can be a bit rigid and prone to cracking. TPU, on the other hand, is all about flexibility—absorbing shocks and providing a grippy, comfortable feel. It’s durable against oils and abrasions but lacks the crystal clarity of PC. Some hybrid cases blend PC and TPU, combining the best of both worlds: the toughness and scratch resistance of PC with the flexibility and shock absorption of TPU.

Thanks for reading! For any suggestions or inquiries regarding this article, feel free to contact the author at brand@evelatus.com.

Did this article help you? You might also find this one helpful: What are shatterproof screen protectors made of?