Introduction Of Thermoplastic Materials Such As PEEK And PEI For 3D Printing

  The first synthetic polymer was developed by John Wesley Hyatt in 1869 as an alternative to ivory. We can't imagine life without polymers right now. It is understood that in 2015, more than 320 million tons of polymers (excluding fibers) were produced worldwide, a large number of thermoplastics entered the automotive industry (reducing weight and reaching higher fuel efficiency standards), and more than 70 million tons of thermoplastics were used in textiles, mainly clothing and carpets, every year. But one of the most interesting thermoplastics is high-performance thermoplastics, designed for very demanding applications. Although they account for less than 1% of the total market share of all thermoplastics, they are becoming increasingly important due to their potential in industries that require high heat resistance, chemical reactivity, mechanical strength, recyclable and lightweight materials.

Properties of thermoplastic materials?

  Today, industrial 3D printing has used high strength thermoplastic peek, PEKK and PEI in many engineering applications in difficult environments. When 3D printing is combined with thermoplastic, it can produce optimized and high-quality parts for practical use.

  "Ultra high polymer at high temperature (over 300 ℃)" ° C) Stable, chemical and radiation resistant, compatible with many enhancers, stronger than many metals, and with high mechanical properties, make them attractive for industrial applications in various industries, such as aerospace, oil and gas, nuclear power, marine, biomedical, tools and automotive industries. " Avalos, one of aon3d's research scientists, said.

  Since 1985, polymer is often used in 3D printing. Peek and PEKK are semi crystalline (now there is amorphous PEKK), while Pei is amorphous. According to Avalos, the glass transition temperature (TG) determines the state of the polymer, that is, "the temperature at which the polymer changes from an amorphous state to a more flexible rubber state.". These "semi crystalline polymers" are crystalline at the same time (for example, peek is extremely resistant compared to most other plastics, TG 143) ° C. The melting temperature is 343 ℃ ° C。

  "Thermoelasticity also means that some high-performance thermoplastics are resistant to thermal degradation and compatible with ultra-high vacuum applications, which are necessary for many use cases in the aerospace industry and biomedical fields - making them ideal for parts that need to be sterilized at high temperatures."

  In addition, peek has excellent mechanical and chemical resistance, which is of great interest to the automotive industry, because of its heat resistance, high strength and durability, it can withstand the temperature under the hood, and it can achieve functional prototype design at a lower cost than before.

  Medical grade and implantable biomaterials, such as PEEK, can also be used in nervous system applications to help control epilepsy, Parkinson's disease, brain trauma, and even spinal fusion devices. Peek has the greatest clinical impact in the field of spinal implant design, and has been widely accepted as a radioactive substitute for metal biomaterials in the spinal community. After confirming its biocompatibility 20 years ago, Paek is increasingly used as a biomaterial for plastic surgery, trauma and spinal implants.

  Avalos explained that heat resistance is an important quality of thermoplastics, and the ability to withstand extreme temperature conditions is one of the factors that people consider when using them in the manufacturing process

  "When 3D printing, the crystallization rate is never constant and is largely affected by the environment in which the molten polymer is extruded. Many temperatures in the printing environment affect the printing layer, such as chamber temperature, chamber convection and nozzle temperature. Therefore, rapid changes in temperature between the extruder and the environment may result in a lower overall crystallinity. "

  "PEKK looks like peek and has similar crystallization behavior, but its TG is slightly higher than 160 ° C. And peek was 143 ° C. The melting point of pseudoamorphous grade is 305 ° C. The melting point of the semi crystalline junction is 332 ° C。 Unlike peek, the crystallization rate of PEKK is slightly slower, which makes it easier to control and leads to better layer bonding. " Avalos claims.

3D printing parts with PEKK

  However, many experts also believe that even the most modern version of PEKK is still more difficult to crystallize than peek, which may be the reason why peek is one of the most concerned thermoplastics in the printing market.

  Amorphous, high-performance thermoplastic Pei also has a strong tolerance. Like most amorphous polymers, it has the characteristics of thermoforming ability, translucency, easy adhesion with adhesives or solvents and so on. Because of its chemical resistance to many fluids, it is very popular in aerospace and automotive industry. In addition, Pei is much cheaper than other high performance thermoplastics and has good physical properties, such as high heat resistance, solvent resistance and flame retardancy.

What are the challenges for 3D printing of thermoplastic materials?

3D printing of PEI

  Avalos says some of the challenges of 3D printing high-performance materials include warpage, shrinkage and deformation.

  "Semi crystalline polymers present a unique challenge, as crystallization leads to further shrinkage, resulting in internal stress, which in turn leads to deformation. The crystallization of the lower layer can change the displacement in welding with the lower layer. Thermoplastics usually reduce in volume and keep cooling from the molten state to the solid state. The ambient temperature contained in the chamber and bed has a great influence on the shrinkage of the first layer during deposition. The lower layer will also undergo the same cooling and shrinkage process, resulting in residual stress, which exists in the component and accumulates layer by layer. " "High strength materials like peek and Pei need an actively heated construction chamber, otherwise they will be affected by poor lamination and extremely low strength parts," he said

  Avalos claims that the temperature environment of the extruder, heating chamber and bed is very important in order to avoid shrinkage, change the material from a molten state to a solid state, and reduce residual stresses in the components. Polymer is very popular at present, but in the past, temperature was a big obstacle, so he suggested "printing amorphous polymer at room temperature and bed room temperature as high as possible, keeping the bed temperature as close as possible to Tg, so as to keep the temperature of the whole environment consistent." At present, some 3D printers have been designed in this way.

  He also suggested that "understanding the material of the construction plate and its interaction with the printing material" is the key, because all the first layer adhesion will lead to warpage, and too high bed temperature will lead to too strong adhesion during the first layer implantation, and finally it is difficult to remove the components, which may damage the bed and components; However, if the bed is too cold, the first layer may not adhere firmly, and the part may warp during printing.

  "For amorphous and semi crystalline materials, the environment of layer welding must be carefully controlled to ensure good part strength."

  In some cases, the performance of thermoplastic products in terms of weight ratio and stiffness ratio is even better than that of metals, but thermoplastic products are not cost-effective in mass production, and can not print very large parts.