LinkedIn

Today, we'll delve into the world of regrind and its impact on plastic part production.  Regrind offers a solution to minimize plastic waste. However, it's crucial to understand the technical considerations and challenges that come with using regrind effectively.

Challenges with Regrind

Using regrind can lead to various issues like contamination, inconsistent pellet configuration, glass fiber breakage, and polymer degradation. These problems can wreak havoc on dimensional control, processing consistency, and the overall quality of the final plastic part.

Contamination is often the result of improper material handling. To avoid this, it's 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.

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.

One common misconception about regrind is that it might process better than virgin material. While this may be true in certain cases, such as when dealing with hygroscopic resins with hydrolytic degradation or thermally degraded materials, it's important to note that the mechanical properties of the regrind are compromised. As a result, the final parts molded from regrind will have diminished mechanical attributes, which can impact their performance in applications.

Consideration for Regrind Particle Size

Another crucial factor to consider is the particle size of the regrind. The size of the particles, whether big chunks, small chunks, 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. 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.

Methods of Regrind Use

There are several schools of thought on how to handle regrind in plastic part production:

1. The 75-25 Blend Ratio: This method, commonly recommended by many material suppliers, suggests using a blend of 75% virgin material and 25% regrind. This approach typically works well if the regrind is consistent in pellet configuration, free from contamination or degradation, and blended properly. However, it's essential to evaluate the mechanical property implications of using this method, especially when using glass-filled materials.
2. Cascade Regrinding: This innovative method involves using 100% virgin material in the first production run. The regrind generated from this run is marked as "first generation" and used entirely in the second production run. The process continues for subsequent runs until all the regrind is utilized. While this approach may work effectively for certain applications, it might not be ideal for hygroscopic materials due to moisture uptake and drying concerns. It may also pose challenges in demanding applications that have specific mechanical requirements, especially for glass-filled materials.
3. Application-Specific Usage: The third method focuses on tailoring the use of regrind to the specific requirements of each part. Some parts may tolerate using 100% regrind, while others demand 100% virgin material to meet stringent product and performance criteria.

Regrind undoubtedly has a significant role to play in reducing waste 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!

Visit our Technical Solutions page.