7 Method Whether the Injection Molded Parts Use Recycled Materials
Introduction
In the plastic injection molding industry, it’s well-known that adding re-grind resin (recycled materials) is common practice. The industry claims that due to current economic pressures and the emphasis on environmental protection, it’s nearly impossible to remain profitable without using some recycled materials. However, from a quality standpoint, adding secondary materials can weaken the plastic due to differences in material properties, leading to reduced strength and potential cracking.
What is Recycled Materials in Injection Molding?
Recycled materials in injection molding refer to plastic resins that have been used before and then processed to be reused in new products. Unlike raw materials, which are used for the first time, recycled materials have been processed for reuse. These materials are typically sourced from post-consumer waste, such as old plastic containers, or from post-industrial scrap, like production leftovers.
Recycled materials are processed to remove impurities and then re-granulated into pellets for use in injection molding, where they are melted and formed into new parts.
Source of Recycled Materials from Plastic Waste
Recycled materials in injection molding can come from various sources:
Post-Consumer Recycled (PCR) Materials: These come from products that have been used by consumers and then collected, cleaned, and processed for reuse. Examples include recycled plastic bottles and containers. These materials often come from municipal solid waste, which includes items like plastic bottles and containers.
Post-Industrial Recycled (PIR) Materials: These are waste materials generated during the manufacturing process, such as defective parts or production scraps, which are collected and reprocessed.
Pre-Consumer Recycled Materials: Similar to PIR, these are materials generated as waste during the production of new products but before they reach the consumer.
Regrind: This is scrap material or defective parts from the same manufacturing process, ground into small pellets and reused in new production.
Reclaimed Materials: These are materials recovered from end-of-life products or waste streams that are cleaned and reprocessed for new use.
How to Prevent Injection Molding Companies Using Recycled Materials for Your Project?
To control the use of recycled materials, it is crucial to specify the type of injection molding materials allowed in the project.
First, explicitly state on the design drawings that no recycled materials are allowed. Second, conduct random audits of the production process at the injection molding facility.
Additionally, by controlling the Melt Flow Index (MFI) of each batch of plastic material and spot-checking the MFI of the final product, it’s possible to ensure the plastic’s quality with over 99% accuracy.
How to check if recycled materials are used in injection molded parts？
If you’re an auditor at a plastic factory, do you know how to check if the factory is secretly using recycled materials? Visual inspection of plastic pellets can reveal irregularities indicating the use of recycled materials.
#1. Melt Flow Index (MFI) Testing:
Test the MFI of the finished product and compare it to the expected MFI of virgin materials. Significant differences in MFI may indicate the presence of recycled content, which can affect the mechanical properties of the final product.
MFI data is a reference point. For the same injection molded part, a higher MFI usually indicates a higher amount of recycled material used.
#2. Visual Inspection:
Look for irregularities in the resin pellets or the final product, such as inconsistent shapes or colors, which can indicate the use of recycled materials.
Black products are more likely to contain recycled materials since black can hide many colors. Therefore, it’s important to specifically inspect black resin for possible regrind.
Another issue is that dyeing and modification plants may also add recycled materials, which are hard to detect visually. To identify this, first check the Melt Flow Index (MFI), then test the impact strength to ensure it meets specifications.
If the recycled material added is scrap from the original batch, there’s less concern about color mismatches. However, there’s still a risk of degradation. To avoid any issues, it’s best not to allow the use of recycled materials, even if they come from the same resin batch.
#3. Supplier Documentation:
Review material certifications or documentation provided by suppliers to check if recycled materials are disclosed. Reviewing supplier documentation can provide insights into the recycling process of the materials used.
#4. Random Audits:
Conduct unannounced inspections of the manufacturing process to check for the presence of recycled materials in the hoppers or drying bins. Random audits should include monitoring the injection moulding process to ensure no recycled materials are used.
During a random inspection at an injection molding factory, take a handful of resin directly from the drying bin or hopper. Normal resin pellets are smooth, cylindrical shapes with clean-cut ends.
In contrast, recycled materials are usually irregular in shape, as they come from reprocessed scraps or defective products. These differences are easy to spot. However, it’s impractical to monitor the factory 24/7.
If the recycled material has been reprocessed into new pellets, it becomes harder to distinguish, but subtle differences in shape might still be noticeable. Pay close attention to these details and question the factory if you notice any unusual pellets.
#5. Impact Strength Testing: Evaluating Mechanical Properties
Perform tests on the product’s impact strength, as recycled materials can reduce durability and make the structure more brittle. Additionally, recycled materials can also affect the chemical resistance of the final product, making it more susceptible to damage.
Products with added recycled materials tend to be more brittle. You can perform a destructive test by forcibly breaking the product. If it snaps with a loud “crack” and the break shows significant whitening, it likely contains recycled material.
#6. Density Measurement:
Measure the density of the material and compare it to the known density of virgin materials. Measuring the density of materials like high density polyethylene can reveal variations indicating the use of recycled content. Recycled materials might cause slight variations.
#7. Laboratory Analysis:
Send samples to a lab for detailed analysis, which can detect the composition and presence of recycled content. Lab analysis can also identify materials with a relatively low melting point, which may indicate the use of recycled content.
You can also check if the amount of resin purchased by the factory matches the amount of finished products produced. Investigate any discrepancies and track where the scrap material (regrind) goes. The formula is: Resin Purchased = Resin in Inventory + Finished Product Output + Scrap Material.