Premiered: 05/02/2026 START ROTO #3

Start Roto SR#03 | LDPE x HDPE: choosing the right resin in practice — LIVE

In Start Roto SR#03, we show how to differentiate LLDPE and HDPE in practice, control recycled material, pigmentation, and reprocessing to avoid warped parts.

1:05:18 OF TALK 12 CHAPTERS YOUTUBE

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What you gain by watching

You learn to differentiate LDPE and HDPE in practice and to avoid the wrong resin before it turns into a warped part or a recurring problem.
You understand the complete path from powder to pellet, from grinding to the extruder, and how to control recycled material, pigmentation, and reprocessing without guessing.
You come away with criteria to choose a partner, prepare your workforce, and recover material more safely on the factory floor.

About the episode

Is every polyethylene suitable for rotomolding? On the factory floor, that question comes up when the bag arrives unmarked and nobody knows whether it's high or low density. In Start Roto SR#03, we went straight to the painful point: the wrong choice between LDPE and HDPE costs you dearly in the part, and recycled material without hardness control is a real trap. We've seen the era of medium density and few micronized options, and we learned in practice — as we recalled in the episode: 'A gente foi aprendendo aí também na cacettada, né, na pancada' — that material analysis is not a gimmick.

Density is not a detail: it's water or honey inside the mold

We showed that density is like water and honey: low density gives you a softer material, high density is harder. Flowability above the ideal makes the plastic swirl inside the mold and form that ball with a thin layer instead of coating the mold in layers up to the right thickness. From there we opened up the cycle: the powder forms the first layer, melts, sticks to more powder, melts again, until closing. The mold needs to rotate and translate to distribute everything evenly. In recovery, the warped part goes back to the mill, is chopped and ground until the granule passes through the ten-millimeter mesh. Then comes the extruder, the heating elements melt it, the screw builds pressure, the degasser removes the air that would ruin the strand, which comes out cooled in water and goes on to the pelletizer. We also talked about how grinding is where pigmentation and material recovery happen, and that additives come in later, right at the extruder's doorstep.

In practice, unmarked bags mixed high- and low-density material, and the solution was literally to bite the pellet: the low-density one is soft, the high-density one is hard. We got to the micronizer, which crushes the pellet until it becomes powder, passes through a screen of about 35 mesh, and sends back whatever didn't pass to be ground again — rotomolding only works with micronized powder, because granules don't melt in the mold. Cold pigmentation only works after the resin has already become powder, and on the factory floor this has even been done in a concrete mixer; the result dirties your hands and isn't suitable for parts in contact with food, so everything depends on the application and the quality of the pigment. Black-market material still circulates because of its low cost, and the question remains: is there a limit to polyethylene reprocessing?

We saw a homemade test: someone thinned the lid of a water tank, stood on top of it, and showed that the strength supported their seventy kilos, saving weight for the company. We understood that plastic recovery can be continuous, as long as the right additives are used to keep characteristics close to the manufacturer's, and that even brittle material can be recovered instead of becoming a lost cause. And as we said in the episode: 'Dá pra você fazer sem roteiro? Dá. É arriscado? Muito arriscado.'

Good recycled material requires the right partner, method, and prepared people

We've seen clients send material to be recovered and get something else back — working with recycled material demands real care for mechanical strength. That's why we talked about the right partner and a prepared workforce. The Essential Rotomolding Course, from science to the factory floor, trains from absolute zero anyone who needs to identify and fix problems without relying on outside consulting. It's two days of theory and practice; on the second day, you smell burning plastic and immediately understand the cause of the problems. In the marketplace, with updated equipment and molds, there's everything from mannequins and crates to fifteen-thousand-liter tanks, plus opportunities like a complete recovery factory and pet line for those who want to enter or expand in the segment. A supplier in our network saw two micronizers break at once and had to scramble to replace them with new machines; what sustains the operation is market knowledge and the strength of sharing what you know. And we remembered: 'Nós não somos os especialistas em tudo. Nós conhecemos, temos a nossa experiência.'

Hit play and watch the full Start Roto SR#03 to choose the right resin and take this knowledge into your production.

Summary generated with AI from the episode; some information may not be 100% accurate relative to the original content.

Episode chapters

1

HDPE, LDPE and the recycled material nobody knows what's inside

We opened Start Roto talking about a topic that scares a lot of people on the factory floor: after all, is every polyethylene suitable for rotomolding? Drawing on our own experience — from when only medium density existed and one or two companies dominated micronized material — we show why the wrong choice between high and low density takes its toll on the part, and we recall that recycled material without hardness control is a real trap. The lesson we take from the conversation is that material analysis isn't a frill: it's what separates a good part from the recurring problem nobody can explain.

We also learned it the hard way, right, by getting knocked around
Watch at approximately 4:34
2

From uncontrolled recycled material to the alphabet soup of polyethylene

We started by recalling why so many people avoid recycled material: until recently it reached the market haphazardly, without density and flow control, and only those with know-how, like partner companies that work with recycling masterfully, can turn that into an advantage. In the same way, we explain the so-called alphabet soup — LLDPE, MDPE and HDPE — showing that density is like water and honey, that low density gives a softer material and that flow above the ideal makes the plastic roll inside the mold and form that ball with a thin layer instead of coating the mold in layers up to the right thickness.
Watch at approximately 9:59
3

How powder becomes a part: the resin cycle inside the mold

Have you ever stopped to think about how that polyethylene powder becomes a box that's smooth inside and out? We explain in a simple way the back-and-forth of the material: the powder resin forms the first layer, melts, sticks more powder, melts again, alternating until closing — and that's why the mold needs to rotate and translate to distribute everything evenly. From there we show the complete cycle starting with recovery: the part that came out warped goes back to the mill, is chopped and ground until the granule passes through the ten-millimeter mesh, ready to return to the process.
Watch at approximately 15:11
4

From the mill to the spaghetti: how leftovers turn back into input material

We opened up the equipment on screen and showed how the leftover box turns back into raw material: the rotating and stationary blades keep cutting everything into smaller and smaller pieces until the flake passes through the ten-millimeter screen, and each cycle depends on the degree of contamination and the requirements of your product. Once the material is ground, it goes into the extruder, where the heating elements melt it, the screw builds pressure, and the degasser removes the air that would ruin the spaghetti — which comes out cooled in water and goes on to the pelletizer, closing the recovery loop.
Watch at approximately 20:23
5

The pellet's journey: from grinding to the extruder, with a cable in the way

Before the material becomes pellet, there's a step that almost goes unnoticed: it's during grinding that pigmentation and material recovery happen, and only after that does the additivation come in, already at the extruder's doorstep. Meanwhile, we were tripping over a ten-meter cable with three splices to get the sound working — and even so we kept showing the spaghetti turning into pellet, because on the factory floor the process doesn't stop for a detail.

After you ground it, right? Before going into, into the extruder, you usually do this additivation, right?
Watch at approximately 25:26
6

The extruder's hollow spaghetti and the color that can't stain

That pellet that comes out of the extruder with a hole in the middle looks like a silly detail, but that's where the fight begins between the natural material and the final color the customer expects to receive without stains. We discussed why many people still prefer hot pigmentation, even though it's the more laborious path, and we showed how having the natural material in stock with the right equipment allows you to make the shade on demand — including remembering the names of the injection molding machine's zones, each with its own temperature, so as not to degrade the material before it becomes a product.

If you have the natural material and have the right equipment for it, you can already make the shade.
Watch at approximately 30:26
7

Biting plastic to know which resin is in the bag

On the factory floor, unlabeled bags mixed high- and low-density material and nobody knew what was in there anymore — and the solution was literally to bite the pellet: the low-density one is soft, the high-density one is hard. It was in that conversation that we got to the micronizer, which grinds the pellet until it turns to powder, goes through a screen of about 35 mesh, and sends back what didn't pass to be ground again, because rotomolding only works with micronized material — granule doesn't melt in the mold.
Watch at approximately 35:31
8

Nego de fumo, concrete mixer and the limit of reprocessing: what decides the color and strength of the rotomolded part

Cold pigmentation only works after the resin has already turned to powder, and on the factory floor this has even been done in a concrete mixer — but the result dirties your hands and isn't suitable for parts in contact with food, which shows that everything depends on the application and the quality of the pigment. We also talked about nego de fumo, which still circulates on the market because of its low cost, and we opened the door to the lingering question: is there a limit to reprocessing polyethylene?

The pigment doesn't just give color. There are also some characteristics of the pigment that have to be taken into consideration
Watch at approximately 40:45
9

When a homemade test proved that the material could handle the job

Someone from our circle tightened the lid of a water tank, climbed on top of it, and showed that the material's strength supported his seventy kilos, saving weight for the company. From there we understood that plastic recovery can be continuous, as long as the right additive is used to keep the characteristics close to the manufacturer's, and that even brittle material can be recovered instead of becoming a lost cause.

We always say that every material, every plan you're going to make for your business, depends on what you're going to produce, right? Can you do it without a script? You can. Is it risky? Very risky.
Watch at approximately 45:49
10

Recycled material requires the right partner and prepared labor

We've already seen a customer send material to be recovered and get another one back — working with recycled material requires real care with mechanical strength. That's why the next episode will open up the topic of reuse in practice, and we take the opportunity to remind you that the Essential Rotomolding course, from science to the factory floor, trains from absolute zero those who need to identify and fix problems without depending on external consulting — especially since labor is getting harder to find every day and training someone is also passing on your company's culture.
Watch at approximately 51:07
11

Essential Rotomolding Course: first-day theory turns into the smell of burnt plastic on the second

We know that showing basic examples here doesn't replace hands-on time on the machine, so we talked about the Essential Rotomolding Course, on the 24th of [month], two days with theory and practice — on the second, you smell the burnt plastic and immediately understand the cause of the problems. And in the marketplace, with equipment and molds being updated, there's everything from mannequins and bins to fifteen-thousand-liter tanks, plus opportunities like a complete recovery factory and pet line for those who want to enter or expand in the segment.

In practice it's better. A course like this you do in practice, you do a theory session, then you go and put your hands on the machine, smell the burnt plastic
Watch at approximately 56:12
12

When the machine breaks and the community holds the market together

A supplier in our network saw two micronizers break at once and had to rush to replace the machines amid everyone's shock — but what sustains the operation is market knowledge and the strength of sharing what you know. It's that same spirit that drives us: we continue preparing a tour of the rotomolding scene in Brazil and worldwide, and we remind you that here nobody owns the truth — if you have a better solution to a problem, the invitation is to bring it into the conversation.

We are not experts in everything. We know, we have our experience.
Watch at approximately 1:01:13