When you run a plastic extrusion blow molding machine, the workflow is smooth, but waste plastics are an unavoidable part of the process—sprues, off-cuts, defective parts, and purge scrap add up fast. For suppliers like us, we don’t just sell machines; we help our customers turn that waste into a profit stream instead of a disposal cost. After working with 100+ blow molding facilities over the last 12 years, I’ve learned that successful recycling isn’t just about tossing scrap into a bin—it’s about tailored, step-by-step systems that fit the rhythm of your extrusion blow molding line. Here’s what actually works. Plastic Extrusion Blow Molding Machine
First, you need to separate your waste correctly, and that starts right at the machine floor. Most people make the mistake of mixing all scrap together: a small defect from a HDPE milk jug, a purge shot from a PP bottle line, and even leftover resin bags. But extrusion blow molding waste isn’t one-size-fits-all, and cross-contamination is the biggest barrier to reusing it. Let’s break down the types you’ll encounter: Process scrap includes sprues (the plastic holding the part to the mold), flash, and defective parts trimmed off after cooling, which are often the cleanest—they haven’t been in contact with food, chemicals, or external contaminants. Purge scrap is the material you run through the machine to switch resin types or fix melt inconsistencies; this can be slightly degraded, but still usable if isolated. Contaminated scrap might include parts that held harsh chemicals, food waste remnants, or even labels left on recycled resin parts.
The fix here is simple: install dedicated scrap bins right next to each blow molding machine, clearly labeled by resin type (HDPE, PP, PET, etc.) and cleanliness grade. Our team often suggests color-coded lids—green for clean process scrap, blue for purge only, red for contaminated—that’s hard to mix up. I’ve seen customers cut rework waste by 30% just by implementing this small floor upgrade.
Next, you need to process the scrap immediately, because leaving it as loose chunks leads to dust, inconsistent melt, and even safety issues in your machine’s hopper. Loose plastic scrap can’t be fed evenly back into the extruder, which causes melt temperature spikes and reduces part quality. The first step here is granulation. A quality granulator (what we sell as part of our integrated blow molding line packages) will cut your plastic scrap into uniform, small pellets called regrind. The key is matching the granulator’s blade type to your resin: for soft materials like LDPE, you need a slow-speed, low-torque granulator to avoid shearing the plastic too much, which degrades its molecular structure. For rigid HDPE, a high-speed granulator with sharp, hardened steel blades will produce a clean, consistent regrind.
A common mistake here is over-granulating or using dull blades. Dull blades tear plastic instead of cutting it, creating fine dust that can clog filters and ruin extruder screws. We test every granulator we provide to make sure it produces regrind with a particle size between 3mm and 6mm—small enough to feed smoothly, large enough to avoid dust. For facilities producing 1,000+ pounds of scrap a day, we also suggest adding a screen changer to the granulator outlet to filter out any metal or other contaminants that slipped past your initial sorting step.
Once you have clean, uniform regrind, you need to test its quality before you put it back into production. Even clean process scrap has minor degradation—exposure to heat and shear in the extruder changes the resin’s melt flow rate (MFR), which is critical for blow molding. If the MFR is too high, your part will be too thin; too low, and it will tear during molding. We always recommend our customers send a sample of their regrind to a local materials testing lab to measure MFR, tensile strength, and impact resistance. Most HDPE and PP process scrap will have MFR values within 10% of virgin resin, which is perfect for reuse. Purge scrap, though, can have a 20-30% lower MFR, so it should only be blended with virgin resin at a 25% max ratio to avoid defects.
Another quick check: check for moisture. Plastic scrap that’s been stored outside or exposed to humidity will have water molecules trapped inside. When you melt that, the water turns to steam, causing bubbles in your finished parts—called “voids”—that are a major quality flaw. We always advise our customers to dry regrind in a hot air dryer for 2-4 hours at 180°F (82°C) before blending. For PET scrap, you need a desiccant dryer, since PET is more hygroscopic, but for most blow molding resins, a standard hot air dryer works.
Now, the blending step is where you balance cost savings with part quality. You can’t just dump 100% regrind into the extruder and expect the same part quality as virgin resin. The sweet spot we’ve found is blending 10-40% clean process regrind with virgin resin, depending on the part’s end use. For non-critical parts like shipping drums or toy housings, you can go up to 50% regrind. For food-contact parts, you have to stick to local regulatory limits (the FDA allows up to 25% regrind from the same food-contact resin, as long as it’s not contaminated).
We’ve seen customers create custom blends that fit their specific machine and parts. For example, a company making HDPE detergent bottles blends 30% clean process regrind with virgin HDPE, adding a small amount of regrind from recycled milk jugs (sorted to match their resin) to cut costs even more. The key here is consistency—if your blend ratio changes, your MFR changes, which leads to machine downtime and defective parts. That’s why we offer optional blending systems that automatically mix virgin resin and regrind at a fixed ratio, so you don’t have to rely on manual scooping.
What if you have more scrap than you can reuse in-house, or your scrap is contaminated (like off-spec resin from a new batch)? That’s where external recycling comes in, and it’s not a last resort—it can be an extra revenue stream. First, make sure you sort this scrap properly: separate different resins, remove any metal or paper labels, and grind it into a uniform regrind. Many regional plastic recyclers will pay $0.10-$0.30 per pound for clean sorted HDPE and PP regrind, which offsets disposal costs. Just make sure to research local recyclers’ requirements—some only accept certain resin types, others require regrind to be a specific size or moisture level.
One thing to watch out for: don’t send mixed resin scrap to recyclers. A single pound of HDPE mixed with PP can contaminate an entire batch of recycled resin, making it unusable and costing you more in scrap fees than you’d save in recycling. That’s why our initial sorting step is so critical—even if you’re recycling externally, separating resins saves everyone time and money.
Now, what about the waste that’s too degraded to reuse or recycle (like heavily contaminated parts or purge from multiple resin types)? For that, energy recovery is a compliant alternative to landfilling in most countries. Modern waste-to-energy facilities burn non-recyclable plastic waste to generate electricity, and they’re far more efficient than landfilling. Just make sure the facility you use meets local environmental regulations—you don’t want to get fined for burning plastic in an unregulated incinerator. We always advise our customers to check with your local waste management provider to see what energy recovery options are available in your area.
I’ve heard too many operators say “recycling is too much hassle” or “the cost isn’t worth it.” But after working with blow molding lines for years, I can tell you that a good recycling system saves an average of $12,000 per year per machine in disposal and material costs, while reducing your carbon footprint by 40% (according to the American Chemistry Council, recycling plastic uses 70% less energy than making virgin plastic). And when you combine that with the right equipment, it doesn’t have to add more work to your team—we design all our integrated blow molding systems with built-in scrap handling that lets operators toss sprues right into the granulator bin without extra steps.
If you’re running a plastic extrusion blow molding machine and want to cut down on waste, improve part quality, or explore tailored recycling solutions for your facility, we can help. Our team has the expertise to audit your current workflow, recommend the right sorting, granulation, and blending equipment, and work with you to set up a recycling system that fits your production volume and budget.
If you’d like to discuss your specific needs, connect with us to learn more about how our solutions can reduce your waste costs and boost your bottom line.
Plastic Extrusion Blow Molding Machine References:
- American Chemistry Council. (2023). Plastic Recycling and Circular Economy Report.
- Society of Plastics Engineers. (2022). Extrusion Blow Molding Waste Management Best Practices.
- U.S. Environmental Protection Agency. (2021). Sustainable Practices for Plastic Manufacturing Facilities.
Dongguang Golden Sincerty Machinery Manufacturing Co., Ltd.
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