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

What you gain by watching

• Learn how to choose between LLDPE, MDPE, and HDPE in practice and avoid costly production errors.
• Discover how to safely recover defective material and master the grinding and extrusion process, without surprises on the factory floor.
• Understand the secrets of pigmentation, density, and flow that define the final quality of your part.

Episode chapters

1. 1

   HDPE, LDPE and the risk of the wrong material in your part

   In this episode, we started late due to technical issues — and even Osmar got the blame — to talk about a subject that keeps factory floor workers up at night: after all, does every polyethylene work for rotomolding? With over 25 years in the market, Júlio César recalls the time when only medium density material existed and shows how the evolution to HDPE and LDPE brought benefits, but also traps for those who don't properly analyze what they're using — including the challenge of recycled material and the need for rigorous process control.

   Back in the day, medium density was used a lot, but I think that was from when I started, right? That was over twenty years ago.

   ▶ Watch at approximately 4:34
2. 2

   Trusted recycled material: why partners with technical control make a difference in rotomolding

   When it comes to recycled material, the lack of flow and density control can become a headache in production — and that's exactly what led us to value partners who master recycling, like Reciplast. In this section, we show how choosing the right polyethylene avoids problems and explain, simply, what the acronyms LDPE, MDPE, and HDPE mean, using everyday examples like water and honey or soda caps. And we reveal a practical secret: material fluidity directly influences part formation, and beginners need to understand this to validate products without surprises on the factory floor.

   I tell people that the plastic is there as powder, it melts, it paints the mold each time it passes.

   ▶ Watch at approximately 9:59
3. 3

   Material recovery: the path of a defective part back to the production cycle

   When a part comes out warped or defective, the immediate question is: can this material be reused? In this section, we show that yes, it can, and the path starts at the grinder, where the part is shredded until it becomes granules. We explain the importance of the right mesh, the proper blade, and the different types of grinders, and how this recovered material can return to the process — always remembering that the secret lies in movement and patience, like when the powder layers up until it forms a part that's smooth on the inside.

   We'll try to explain, even through the slides here, what each of these machines does in the recovery process, and some even work for virgin material too, right?

   ▶ Watch at approximately 15:11
4. 4

   From flake to noodle: the complete path of plastic recovery in the grinder and extruder

   When the colored material comes out of the grinder, the question that remains on the factory floor is: how to turn that flake into something usable again? We opened the equipment and showed each stage — from the three blades that cut the box into increasingly smaller pieces to the ten-millimeter screen that defines the grinding cycle, and then we followed the material to the extruder, where the heaters melt everything and the screw, which gradually reduces in size, creates the necessary pressure to eliminate gases and prevent bubbles that ruin the noodle. At the end, we revealed the detail many miss: the standard chopper size is what determines the ideal thread thickness, and for those wanting agility, the ground flake can go straight to the injection molding machine without going through this process.

   It also gradually reduces the screw size to create pressure… it's to eliminate gases, so it's not releasing bubbles either.

   ▶ Watch at approximately 20:23
5. 5

   The sound that fails and the pellet that is born: behind the scenes from grinding to extrusion

   In the middle of the explanation about the grinding stage, we discussed how pigmentation and material recovery happen right there, before the compound moves on to the extruder — and it was precisely at that point that the audio began to fail, with a ten-meter cable and three splices that couldn't handle the sea air. While we tried to resolve the technical issue, we returned to the factory floor to show the already-cut pellets, remembering that it's after grinding and adding additives that the material enters the machine and becomes that thread which, at the end, turns into the grain ready for the process.

   Okay, folks, we were explaining that here, look, these are the pellets after cutting that noodle.

   ▶ Watch at approximately 25:26
6. 6

   Why does the extruder degrade your material? The answer lies in the temperature zones

   When we look at that hollow noodle coming out of the extruder, we raise the question many have on the factory floor: why does it come out like that and how does the machine's configuration influence the result? The conversation led us to a crucial point for those working with rotomolding: the pigmentation of natural material, whether hot (more common, yet labor-intensive) or cold (which requires proper equipment to avoid staining). And it was then that we told the real case of a client who prefers hot pigmentation precisely because of staining problems, but we showed that, with the right investment, cold pigmentation can free your company from giant inventories of various colors, allowing you to create the exact shade with more agility and control — without having to pass the material through the extruder again and risk degradation.

   Folks, I remembered the name there, I was trying to remember the injection molding machine there. It's called zones, it has zone one, two, three. Why? Because each zone there has its own temperature.

   ▶ Watch at approximately 30:26
7. 7

   How to identify plastic density by biting the pellet — and why rotomolding requires micronized powder

   On the factory floor, mixing high and low density material is a classic mistake — and we tell how a flexible little screen for Nescau lids caused headaches at the injection machine, with poorly identified bags and the practical solution the worker uses: biting the pellet to feel if it's soft or not. From there, we follow the path of the material to the micronizer, explaining the conical knife, the mesh 35 sieve, and why the grain that doesn't become powder simply doesn't melt in the mold. We close by showing that rotomolding only works with micronized powder, and by the way we remember Clei, a plastisol specialist, who still comes to visit us to talk about this other liquid approach to rotomolding.

   I used to have a habit of taking one of those little pellets and chewing on it. It just kept growing, became a little plastic.

   ▶ Watch at approximately 35:31
8. 8

   Cold and hot pigmentation: when the powder decides the color of your part

   In this section, the conversation revolves around the behind-the-scenes of pigmentation in rotomolding, showing that there isn't a single recipe: the material must be in powder form for cold pigmentation, but the choice between it and hot pigmentation depends on the final application of the product. We tell how pigment quality can even weaken the part or make it translucent, a risk for water tanks and other tanks that need to block light. And we also remember the old 'nego de fumo' (a type of pigment), which still appears in applications for cost reasons, but no longer has a place in modern rotomolding.

   Because the pigment doesn't just give color. There are some characteristics of the pigment that also need to be taken into consideration.

   ▶ Watch at approximately 40:45
9. 9

   Resistance on the factory floor: the case of the lid that supported 70 kilos and choosing the right polyethylene

   On the factory floor, the choice between low and high density polyethylenes can define the success or loss of a product, and we tell the real case of an acquaintance who proved the strength of a water tank by thinning the lid, reducing weight, and stepping on it to demonstrate the quality of the material. We also explore the limits of plastic recycling, which requires constant additive use — unlike aluminum — and how small resources like zinc stearate help circumvent problems without losing ideal fluidity or density. We close by highlighting that all planning depends on what you want to produce, because without a roadmap the risk of wasting money and time is high, and we anticipate that we will bring specialists to talk about a new powder mold release technology that promises to change the game in rotomolding.

   No wind is favorable when you don't know where you want to go.

   ▶ Watch at approximately 45:49
10. 10

    Free rotomolding course: the shortcut to identify and fix flaws before paying for consulting

    The conversation exposes a real risk on the factory floor: material recovery may not go as expected and, without basic knowledge, the rotomolder pays a high price for it. At the close of the episode, we announced the free course that previews the Rotomolding Essentials, showing how a trained team can diagnose problems on the spot without spending on external assistance, and we also mentioned the case of a participant who, without ever having touched a part, pointed out the cause of a flaw on the second day of hands-on class.

    Wow, look, this is like this, fix it like this, so on, so on, picked up a damaged part, identified the problem and said: "This happened this way.

    ▶ Watch at approximately 51:07
11. 11

    Essential rotomolding course: theory, practice, and the smell of burnt plastic

    In this segment, we talked about the limits of learning rotomolding only here and reinforced that nothing replaces an in-person course, where you smell burnt plastic and see eyes watering from unregulated gas. That's why we shared that the Essential Rotomolding Course has two days — one theoretical and one practical — and it's in practice that everything falls into place, like when the student finally understands the cause of problems. We also updated the marketplace with new equipment and molds, including a complete recovery plant, and previewed the schedule of episodes with experts in burners, heavy machining, and micronizers, always seeking to bring knowledge straight from the factory floor.

    Nothing beats having an in-person course, where you'll look, you'll see, we'll be exchanging information there, with more time than one hour of course here.

    ▶ Watch at approximately 56:12
12. 12

    When even the specialist breaks down: the time to chase new machines and what's coming next in the global market

    We shared a real case of a supplier who, despite being experienced, saw two micronizers break on the same day — panic took over, but the solution was immediate: chasing new equipment to not leave anyone hanging. And that led us to reflect on how no one owns the truth in this industry, there's always something new to learn or a simpler way to solve a problem — so we opened the floor for anyone wanting to share their own solution. In the end, we also teased: how is rotomolding doing worldwide? In the next episode, we'll show what companies abroad are doing differently and how Brazil compares in that global scenario.

    We don't know, we don't own the truth — a person learned to work for thirty years, but they're still stuck in that old way.

    ▶ Watch at approximately 1:01:13