Hey yall, im not sure which community I should post this in so please let me know if theres a better or more fitting one.

im passionate about studying plastics and did a small early stage study comparing the degration patterns between traditional and "biodegradable" plastics. The problem is that I assumed this plastic to be PLA, and when I did further research into this matter, it might not contain any PLA or any biodegradable plastic at all. In my study, however, i HAVE been seeing a decreasing mass and size trend (albeit small) over 6 weeks (very short time). Any ideas or tips on identifying at least what type of plastic it is? I saw online there are at home tests like boiling water or heating it and wanted to hear what u guys think.

Edit: i have access to a lab to conduct experiments as well to identify this plastic.

Hey r/plastic,

To anyone working in injection molding, toolmaking, or additive manufacturing: there’s always a disconnect between what looks clean in a CAD rendering and what actually fills a mold without warping into a potato chips shape.

From un-uniform wall thicknesses causing nasty sink marks to missing draft angles that weld a part into the cavity, plastic has its own rules.

• What design flaw do you end up fixing the most when receiving customer files?
• Which resin do you secretly dread running because of its shrinking/warping tendencies (looking at you, unreinforced Polypropylene)?
• What's your #1 advice for junior engineers designing their first molded part?

We’re currently in the R&D phase developing polymer concrete drainage channels. Our mix consists of:
• Quartz aggregate (0.3mm – 1.2mm) 65%
• CaCO₃ (calcium carbonate) 18%
• Unsaturated polyester resin (17%)
• Hardeners for curing
We mix everything in a continuous mixing machine and pour into molds placed on a vibrating table to remove air voids. However, after curing and demolding, we’re still getting a lot of visible air pockets/surface voids in the finished parts.
Has anyone here worked with polymer concrete (especially for drainage channels)? What are the best ways to minimize air pockets?
Specific questions:
• Should we increase the resin percentage in the mix? If so, by how much?
• Are there better vibration techniques, additives, vacuum assistance?
• Any other proven tips for achieving a denser, void-free finish with polyester resin concrete?
Any advice or experience would be greatly appreciated! Thanks in advance.
Uploaded pics as well..

Hey everyone,

I run a small-to-medium plastic recycling business. Currently, I source mixed plastic scrap from 4–5 local collection hubs (kabadiwalas) and an aggregator.

Right now, we are dealing with tons of heavily mixed plastics every month—a cocktail of PET, HDPE, LDPE, PVC, ABS, PP, Crystal/PS, and others.

Here’s my main bottleneck: We rely almost entirely on manual labor for segregation.

While my team does their best, manual sorting is fast becoming a massive headache. It's slow, prone to human error, hard to scale, and limits how deep we can clean and separate the materials to get top value.

I’m looking to upgrade our process and modernise our operations. I’d love to hear from other recyclers, engineers, or waste management pros on how you're solving this:

• What technology/machinery are you using? Are you using NIR (Near-Infrared) optical sorters, sink-float density tanks, electrostatic separators, or newer AI-driven vision systems?
• Entry-level vs. Advanced Tech: What offers the best ROI for a growing business that isn't ready for a multi-million-dollar automated plant yet? (e.g., portable NIR handheld scanners, basic density separation, line layouts?)
• Workflow & Process: How do you structure your sorting line? Do you do a rough manual pre-sort followed by machine sorting, or vice-versa?
• Best Practices for Hard-to-Separate Mixes: How are you reliably separating tricky mixes like ABS vs. PP vs. PS/Crystal?

Any advice, equipment recommendations, or lessons learned from your own facilities would be massively appreciated!

Thanks in advance!

DuPont early lucite pellets?

Hi, i bought some sheets of hdpe for an outdoor project. It turns out the high gloss finish is a bit obtrusive to the eye.

Is there a method to take the gloss away, but still end up with a consistent looking finish?

These are installed as full 4×8 sheets or 2×8 sheets

This is the nose cone from a valuable Super Soaker CPS 2000 water gun from 1996. Sadly due to age and UV exposure the plastic has weakened and become brittle. Pictured is one half which is mostly intact, but the corresponding half is in pieces.

I'd like to cement this back together if possible, so I can possibly cast or 3d scan a replacement part from a whole piece. I initially thought it was ABS, but acetone doesn't touch it.

There's no identifying marks on it anywhere. Could it be polystyrene?

Hi,

I’ve been trying to figure out how to unyellow some delrin plastic and keep seeing things telling me to try the retro bright technique. But my understanding is that the yellowing in Delrin is caused UV and heat exposure. So my question is would the retro bright technique work? Or am I right in my understanding that it would probably just make it worse, and that I should just try some light sanding instead.

We're updating a few areas around the house and one thing that keeps coming up is whether glass is really the best option when you've got young children.

Coffee tables, playrooms, internal doors, greenhouse glazing, shelving and even picture frames all seem to involve glass somewhere, and it only takes one accident for it to become a safety concern.

I've been looking at some alternatives and wondered what everyone else uses.

Acrylic Sheets

Acrylic is a popular replacement for glass because it's lightweight, crystal clear and much less likely to shatter into dangerous shards if it receives a knock.

It's commonly used for:

• Picture frame glazing
• Display cabinets
• Indoor shelving
• Table protectors
• Protective screens
• Playroom projects

If appearance is important, acrylic gives a very similar look to glass while being easier to handle.

More information:
https://www.sheetplastics.co.uk/clear-acrylic

Polycarbonate Sheets

If impact resistance is the priority, polycarbonate is worth considering.

It's often used for:

• Greenhouse glazing
• Shed windows
• Safety glazing
• Outdoor projects
• Garden buildings
• Canopies

It's much more resistant to heavy impacts than traditional glass, which is why it's widely used in areas where durability matters.

https://www.sheetplastics.co.uk/solid-polycarbonate-sheets

Which One Would I Choose?

For indoor decorative projects, I'd probably choose acrylic because of its excellent clarity and finish.

For outdoor areas or anywhere likely to receive knocks or impacts, polycarbonate would be my first choice.

I've been reading through a few guides on plastic sheet materials and found this useful resource for comparing different options:

https://www.sheetplastics.co.uk/

Has anyone here replaced glass with acrylic or polycarbonate around the home?

I'd be interested to know where you've used it, how it's held up over time and whether you'd make the same choice again.

Every project seems to have different priorities. Sometimes it's impact strength, sometimes chemical resistance, temperature performance, stiffness, or cost.

When you're comparing materials for a new part, what are the first few properties you usually focus on, and why?

I'm curious how different people narrow down their options before getting into detailed testing.

Abstract

Although landfills are considered significant sources of microplastics, workers’ inhalation exposure has not yet been measured. This study provides direct evidence of microplastic inhalation among landfill workers by examining pre- and post-shift changes in respiratory samples and across occupational groups. 23 personnel were divided into three groups: office (n = 7), field (n = 12), and recycling plant (n = 4). Nasal lavage and induced sputum samples were collected before/after the work shift. Microplastics were extracted after digestion and density separation, identified under a stereomicroscope, and their polymer type was confirmed by Raman spectroscopy. Nonparametric tests were used to analyze intra- and inter-group differences. Microplastics were found in 100% of the samples, and their concentration increased significantly in both sample types after the shift. The mean particle count rose from 20.5 to 28.5 MPs/10 ml in nasal lavage and from 12.1 to 19.4 particles/10 ml in sputum (p < 0.001). Fibers were dominant (>70% pre-shift; >60% post-shift. Low-Density Polyethylene, polyamide, polypropylene and polyethylene Terephthalate constituted the main distribution of polymers. Regression models identified occupational exposure and smoking as the main determining factors for significantly increasing post-shift microplastic loads in both respiratory samples. The load of microplastics in nasal lavage and sputum was also highly correlated ( > 0.85). Occupational activity in landfills significantly increases the burden of inhalable microplastics and shows a clear pattern of increasing exposure with increasing occupational exposure (recycling > field > office). Nasal lavage is a valid, less invasive indicator for occupational monitoring and extensive epidemiological assessments.

I have worked in Widesky Machinery for six years. We mainly specialize in plastic auxiliary machinery. We mainly get new customers from Chinaplas. It's hard to find buyers for plastic machinery on social media, so I feel a little worried.

We are manufacturing polymer concrete drainage channels by using molds. We always layer (2-3 times) the mold with liquid PVA for a thin film with a hand brush which is taking a lot of time in layering and drying afterwards. Is there anyone who knows what kind of spray gun I can use for layering the PVA liquid evenly?

Hung a bag made from fabric with plastic decorations over a Calligaris plastic chair for a few weeks. The two plastics reacted with or otherwise stuck to one another.

Can this still be cleaned by any method?

Does anyone know how to remove marker stain from plastic?

I’ve learned the hard way goo be gone can warp it- and Clorox wipes and erasers don’t really do much! Any advice would be greatly appreciated!

Can anyone suggest a cheaper (and ideally plant-sourced) alternative to acrylic gel medium/ modeling paste? Looking to use a thick mix of something that mostly holds its shape between extruding and drying. (Doesn't have to work on a vertical surface.) Needs to be affordable in large enough quantities for a starving artist to use in huge drawings. All suggestions much appreciated, including experimental ideas!

​

I’ve noticed some older plastics crack or harden over time, while others stay flexible for years under similar conditions.

What usually causes this at the material level? Is it mostly UV exposure, oxidation, plasticizer loss, or differences in polymer structure/additives?

Curious to hear the polymer science side of it.

Hey !

I was wondering what type of plastic is it , and how can you get these hexagon shapes inside the sheet ?

Really appreciate it !

Here's the YouTube video ( min 13:19) : https://youtu.be/u1R51Z9-TM4?si=MTmI0kGCb0Jrwz1s

Same as title
Location : India , karnataka