| August 30, 2023
The topic of regrind use is a hot topic in today’s processing world. We will be discussing its impact on plastic part production on this blog. Regrind offers a solution to minimizing plastic use and reducing plastic waste. It is crucial to understand the technical considerations and challenges that come from using regrind effectively.
Challenges with Regrind
The use of regrind can lead to various issues like possible contamination, inconsistent pellet configuration, glass fiber breakage, and polymer degradation. These problems can affect the final part dimensional control, the overall quality of the final plastic part and processing consistency.
Contamination is often the result of improper material handling. To avoid this, it is essential to establish specific and detailed material handling procedures. Properly cleaning grinders and hoppers and keeping material containers covered are just a few of the essential steps that need to be taken to maintain the purity of the regrind. Another method of avoiding contamination is to do the grinding press side and adding the regrind back into the process at the established ratio. This will avoid any possible contamination in a separate part of the plant.
Glass-filled materials commonly exhibit some degree of fiber breakage during processing and regrinding. Using such reground material can lead to reduced mechanical properties, particularly tensile and impact strength. Moreover, maintaining dimensional control becomes more challenging due to changes in shrinkage rates. The extent of these issues depends on the amount of fiber breakage and the quantity of regrind utilized. Low rpm grinders and press side cutting while the runners or parts are warm is an effective method of reducing fiber breakage.
One common misconception about regrind is that it might process better than virgin material. While this may be true in certain cases, it is most likely that moisture or degradation of the material is the cause of the change in viscosity. This is the case when dealing with hygroscopic resins with hydrolytic degradation or thermally degraded materials. Please note that the mechanical properties of the regrind are compromised in these cases and the final parts molded with regrind will have diminished mechanical attributes, which can impact their performance of the parts.
Consideration for Regrind Particle Size
Another crucial factor to consider is the particle size of the regrind. The size of the particles, whether large particles, small particles, or fines, can significantly affect the performance of the regrind. Inconsistent sizes, especially large variations, may lead to non-uniform melting and variable drying rates for hygroscopic resins. The larger the particle, the longer it will take to dry. This can cause issues such as variations in shrinkage, part weights, dimensional results, warpage, functional deficiencies, and even non-melt in the parts, particularly for semi-crystalline materials. Additionally, fines can cause unwanted black specs or discoloration streaks in transparent or translucent materials because of degradation of the fines. Consider using screens with your grinders to greatly reduce adding the fines into the process or separating large particles before they are introduced into the hopper.
Methods of Regrind Use
There are several ways of managing the use of regrind in plastic part production:
Regrind undoubtedly has a significant role to play in reducing waste and cost in the plastics industry. However, its successful implementation relies on establishing proper procedures and disciplines on the production floor. Regardless of the chosen method, it is crucial to ensure that parts produced with regrind are fully qualified to minimize any potential performance risks.
We hope you found this Tech Tip informative and useful for your plastic part production processes. Stay tuned for more insights into the world of plastics in our future blog posts!
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Cesar Alcantar | Senior Application Development Engineer
Cesar currently serves as Senior Application Development Engineer. Cesar has 30 years of experience in the plastics industry. During this time, he has held technical, sales, marketing, and management roles. Prior to joining Nexeo Plastics, Cesar was employed at General Motors, GE Plastics, and Celanese Engineered Materials where he served in several roles supporting their global customer base in most major markets and applications. Here he was responsible for developing new applications for manufactured resins, with a focus on injection molding thermoplastics in the global marketplace. Cesar has extensive knowledge in 6 Sigma processes, QS trained, DFMA, Lean manufacturing, Project Management and Change management, and acceleration and 3D printing processes. His role is to assist customers with material selection, processing challenges, part design, and providing general feedback on new product development. Cesar has a Bachelor of Science in Mechanical Engineering from the University of Texas at El Paso and many years of industry training in injection molding, extrusion, and 3D printing.
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