The choice of polymer significantly affects the mechanical properties and printability of 3D printed objects. Polymers are large molecules made up of repeating units called monomers, and their properties can vary widely depending on their chemical structure, molecular weight, and processing conditions. When it comes to 3D printing, the most common polymers used are thermoplastics, which can be melted and solidified multiple times without significant degradation.Here are some factors that influence the mechanical properties and printability of 3D printed objects based on the choice of polymer:1. Glass transition temperature Tg : The glass transition temperature is the temperature at which a polymer changes from a hard, glassy state to a rubbery, more flexible state. Polymers with a higher Tg will generally have better dimensional stability and heat resistance but may be more challenging to print due to the higher temperatures required.2. Melting temperature Tm : The melting temperature is the temperature at which a polymer transitions from a solid to a liquid state. Polymers with a higher Tm will require higher printing temperatures, which can affect the printability and may require specialized equipment. Additionally, higher Tm polymers generally have better heat resistance and mechanical properties.3. Crystallinity: Polymers can be either amorphous or semi-crystalline. Amorphous polymers have a more random molecular structure, while semi-crystalline polymers have regions of ordered, crystalline structures. Semi-crystalline polymers generally have better mechanical properties, such as tensile strength and impact resistance, but may be more challenging to print due to their higher melting temperatures and potential for warping.4. Flexibility and toughness: The choice of polymer can greatly affect the flexibility and toughness of the 3D printed object. For example, polylactic acid PLA is a rigid and brittle polymer, while thermoplastic polyurethane TPU is highly flexible and elastic. The desired mechanical properties of the final object will dictate the choice of polymer.5. Printability: Some polymers are easier to print than others due to their flow properties, adhesion to the print bed, and resistance to warping. For example, PLA is known for its ease of printing, while materials like nylon and polycarbonate can be more challenging due to their higher printing temperatures and tendency to warp.6. Chemical resistance and biocompatibility: The choice of polymer can also affect the chemical resistance and biocompatibility of the 3D printed object. For example, polypropylene PP has excellent chemical resistance, while PLA is biodegradable and considered safe for use in medical applications.In conclusion, the choice of polymer for 3D printing has a significant impact on the mechanical properties and printability of the final object. It is essential to consider the desired properties of the final object, such as strength, flexibility, heat resistance, and chemical resistance, when selecting a polymer for 3D printing. Additionally, the ease of printing and compatibility with the 3D printer should also be taken into account.