Does silicone as hard as plastic exist?

[Blokle]

I saw rubber-like silicones. Are there types of silicone that can be used in injection molding and once the process is finished - become as hard as, let's say, PVC? At the same time they should have all(/majority) of silicone's properties (citing Wikipedia):

- Low thermal conductivity
- Low chemical reactivity
- Low toxicity
- Thermal stability (constancy of properties over a wide temperature range of −100 to 250 °C)
- Does not support microbiological growth
- Resistance to oxygen, ozone, and ultraviolet (UV) light
- High gas permeability

If such silicones exist - what are their proper names/formulas?

 

[Vanadium 50]

Silicones are plastics, and there is no such material as "regular plastic". There are many such materials. I think your best path forward is to quantify your requirements and see if there is a material that meets them.

 

[Blokle]

As hard as PVC.

 

[Vanadium 50]

You listed seven requirements. You've given us one of them, and even then there's no quantitative information. Additionally, I suspect you also don't mean "hardness", but instead mean "strength". Or possibly "stiffness".

If you can't describe what you want, how will you know when you found it?

 

[Baluncore]

Silicones are limited by the organic component included in the polymer.
If you want more rigid material, then consider silicate minerals, or ceramics.
Zeolites have possibilities for permeable thermal insulation.
Silicon carbide is hard.

 

[Blokle]

You listed seven requirements. You've given us one of them, and even then there's no quantitative information. Additionally, I suspect you also don't mean "hardness", but instead mean "strength". Or possibly "stiffness".

If you can't describe what you want, how will you know when you found it?

1. A good engineer can listen to a non-engineer and understand what he means even when the latter doesn't use precise, correct terminology. You see, you seem to understand what I mean. Quantitative information - comparable to PVC.

2. How will I know? I'll take it in my hands and see whether it is as rigid as PVC or not.

 

[Blokle]

Silicones are limited by the organic component included in the polymer.
If you want more rigid material, then consider silicate minerals, or ceramics.
Zeolites have possibilities for permeable thermal insulation.
Silicon carbide is hard.

Can ceramics (and the others - silicate minerals, zeolites, silicon carbide) be used in injection molding? I thought ceramics is more like glass which needs to be blown molded?

 

[Baluncore]

The material injected can be a composite of materials that enhance the properties you require.

 

[phinds]

How will I know? I'll take it in my hands and see whether it is as rigid as PVC or not.

First you want something as hard as PVC ("Does silicone as hard as plastic exist?") and now you want something as rigid as PVC. It seems pretty clear, as Vanadium has already pointed out to you, that you don't really know WHAT you want, quantitatively. You're expecting our psychic powers to translate your vagueness into hard tech specs.

 

[phinds]

1. A good engineer can listen to a non-engineer and understand what he means even when the latter doesn't use precise, correct terminology.

Sure, in vague, non-quantitative terms that might be a good, informal, start but are nowhere near the end point of actually finding what is needed.

 

[jrmichler]

As hard as PVC.

Plastic hardness is rated in durometer. Engineers understand durometer. A sample pack is a good, low cost, investment to understand what different durometer hardness feel like. A good sample pack costs $25.00 from McMaster-Carr: https://www.mcmaster.com/8450K4/. Highly recommended. And a photo of it:

They also have other sample packs.

 

[Vanadium 50]

I don't think he means hardness. (Resistance to scratching) I think he means strength or stiffness,

 

[russ_watters]

Sure, in vague, non-quantitative terms that might be a good, informal, start but are nowhere near the end point of actually finding what is needed.

In other words, @Blokle a good engineer should be able to help focus you and push you in the right direction, which is what these guys are doing. They aren't mind readers: they need you to help them help you by putting some effort into your responses to them. Be specific. Use the correct language. State your real requirements (don't just parrott back a list; there's no way your requirements coincidentally fall into the range of that list). What, specifically, is the application? What, specifically are the requirements that matter?

 

[berkeman]

A good engineer can listen to a non-engineer and understand what he means even when the latter doesn't use precise, correct terminology.

Here are a couple links to help you get more background in plastics, to help you phrase your questions more precisely (which as mentioned already, helps us to help you):

https://en.wikipedia.org/wiki/Plastic

This link includes a nice table of properties: https://www.britannica.com/science/plastic

 

[Laura85]

Hi,

I know a little about silicones from doing hobby stuff. They usually express the hardness on the Shore Scale (Durometer) Hardness. If you Google the term you get an overview of the different types. The high end of Shore A, silicones, goes as hard as "a shopping cart wheel".

 

[DaveE]

I suggest you talk to the people that do a lot of injection molding. Not people like us that may know something in general about materials. They know the practical issues involved. Things like can you actually buy, for a reasonable cost, the material you want? Is that material compatible with their machines or machines/processes common in industry? Have you considered this other material or process? There is a good chance that they will say "how about this sort of thing that we already make for someone else." If they've never seen what you want, you need to know that upfront, it will have significant implications to your design process and chance of success.

 

[Blokle]

Sure, in vague, non-quantitative terms that might be a good, informal, start but are nowhere near the end point of actually finding what is needed.

I indeed just try to start my quest for the proper material...

 

[Blokle]

I don't think he means hardness. (Resistance to scratching) I think he means strength or stiffness,

By hard/rigid I mean the opposite of elastic, i.e. capable to retain form/shape under pressure.

 

[Blokle]

In other words, @Blokle a good engineer should be able to help focus you and push you in the right direction, which is what these guys are doing. They aren't mind readers: they need you to help them help you by putting some effort into your responses to them. Be specific. Use the correct language. State your real requirements (don't just parrott back a list; there's no way your requirements coincidentally fall into the range of that list). What, specifically, is the application? What, specifically are the requirements that matter?

Thank you, and to all the many forum member who try to help. I'll try to follow your advice and be more specific regarding requirements:

1. capable to retain form/shape under pressure (that's what I meant by hard/rigid).
2. non toxic (as close to "food grade" as possible)
3. low chemical reactivity
4. resistance to oxygen and ultraviolet (UV) light

All the other properties of silicones I mentioned above are also preferred but not a must.

 

[Blokle]

I suggest you talk to the people that do a lot of injection molding. Not people like us that may know something in general about materials. They know the practical issues involved. Things like can you actually buy, for a reasonable cost, the material you want? Is that material compatible with their machines or machines/processes common in industry? Have you considered this other material or process? There is a good chance that they will say "how about this sort of thing that we already make for someone else." If they've never seen what you want, you need to know that upfront, it will have significant implications to your design process and chance of success.

Thank you! This is very wise thing to do and I actually wanted to go this way. Just needed to get some general info/direction about the proper material (material groups) to be able to start the conversations with those guys involved in injection molding. That's why I'm here :)

 

[Blokle]

So does anybody has any suggestions for me, once I have provided additional details? Thank you.

 

[DaveE]

Thank you, and to all the many forum member who try to help. I'll try to follow your advice and be more specific regarding requirements:

1. capable to retain form/shape under pressure (that's what I meant by hard/rigid).
2. non toxic (as close to "food grade" as possible)
3. low chemical reactivity
4. resistance to oxygen and ultraviolet (UV) light

All the other properties of silicones I mentioned above are also preferred but not a must.

Sounds like HDPE or PC to me, except for the UV part. Maybe fillers could absorb the UV.

 

[Vanadium 50]

So does anybody has any suggestions for me, once I have provided additional details?

Sometimes it takes more than 11 hours.

DaveE has some good suggestions - this sounds like HDPE. (This is what water jugs are typically made of) They don't use silicone, but you never explained why you need silicone.

 

[Matcon]

DaveE has some good suggestions - this sounds like HDPE. (This is what water jugs are typically made of) They don't use silicone, but you never explained why you need silicone.

Agreed. Surely the approach is to specify the properties and find which materials fit those properties rather than specify the material and figure out how to modify it to meet requirements?

If you know your materials science, you should be able to work out the microstructure/s that will attain those properties.

 

[DaveE]

I'm having a hard time imagining any polymer that's really UV resistant. But, I guess it's a matter of degree; how resistant?

You may want to consider a structure that keeps the UV away from the plastic; some sort or coating or filler, perhaps.

 

[cmon now]

not sure why these people didnt give you the simple answer to your question .. yes rigid silicon tubing (as hard as pvc)exists commercially that meets all your listed requirements and can come in any shape desired ..

 

[DaveE]

not sure why these people didnt give you the simple answer to your question .. yes rigid silicon tubing (as hard as pvc)exists commercially that meets all your listed requirements and can come in any shape desired ..

Because we are a bunch of physicists, chemists, and engineers that don't actually do any of this fabrication.

But now you've piqued my curiosity. I've seen silicone reinforced stuff (wires and braids etc.) but I'd like to know more about injection molding for rigid silicone. Can you gives us a link? I can't find much.

 

[BillTre]

A good engineer can listen to a non-engineer and understand what he means even when the latter doesn't use precise, correct terminology.

I would like to basically reiterate what @russ_watters said.
I have worked with good engineers on several projects. Getting good answers/advise often involves a discussion with the experts. A lot of back and forth questions and answers to refine what is wanted.

That said, WRT your list:
- Low thermal conductivity
- Low chemical reactivity
- Low toxicity
- Thermal stability (constancy of properties over a wide temperature range of −100 to 250 °C)
- Does not support microbiological growth
- Resistance to oxygen, ozone, and ultraviolet (UV) light
- High gas permeability

Several of these properties:
- Low chemical reactivity
- Low toxicity
- Thermal stability (constancy of properties over a wide temperature range of −100 to 250 °C)
- Does not support microbiological growth
- Resistance to oxygen, ozone, and ultraviolet (UV) light
can be met by polycarbonates and related plastics which the properties vary across. (We used them to produce injection molded fish tanks for fish research labs.)

Not so sure about the resistance to oxygen, ozone, and ultraviolet (UV) light, but this would depend upon the degree of abuse the materials are exposed to. Probably something to quantify.
Never considered thermal conductivity.
Some of these plastics are are more susceptible to degrading in low pH (particular washing solutions)/high temperature (autoclaving conditions).
Resistance to these conditions often trade-off with resistance to breaking (structural strength or impact resistance I guess).
Some of the tanks (maybe 1 mm thick) we produced could probably be drop-kicked across a football field without breaking.

Resistance to UV can be improved by additives such as blue or black pigments (common in a lot of marine products), but these additives often come with toxicity problems (at least for baby fish).
This can get complex, so we would work with the engineers/producers to bioassay particular materials for toxic effects on our fish.
A simple and sensitive bioassay (we developed a good one for fish) becomes essential in the process of identifying suitable materials.
Lack of toxicity to one organism, does not mean a lack of toxicity to all. Some are particularly susceptible to certain compounds.
And again this involves a lot of back and forth discussion with the engineers.

Since your list is longer and probably more exclusive, it might become a more of a complicated process.
Understanding the intended use would be helpful.

When it comes to high gas permeability, you will probably have to be more specific (how much of what gas, through how thick of a material). As the surface area of the material is increased, the amount of gas exchanged will increase (which is why lungs and gills have high surface areas).
There are few plastics I am aware of that are what I would call very permeable to gasses.
This comes down to being able to keep fish alive in a bag of water with no air in it.
There are some commercially available fish bags (breather bags) that do this, but they are very thin plastic and not stiff.
I am also aware of a flexible plastic sheet used in a NASA Xenopus frog housing, on the space shuttle (which might be silicon based) that is used as the gas exchange surface for the container. (Had a friend who was working on a space shuttle project and had me consult on it.) The sheet was about .5 to 1.0 mm thick as I recall. Don't know details of the material, but I'll bet it was expensive.

Cost might also end up on your list.

 

[demodave]

Can ceramics (and the others - silicate minerals, zeolites, silicon carbide) be used in injection molding? I thought ceramics is more like glass which needs to be blown molded?

This is a way belated answer, but yes, ceramics can be extruded or injection molded. It's just, they have to be extruded in a green body, paste-like form. Then they need to pyrolyzed (heated and 200-400C) to get rid of the low temperature volatiles, at which point they are somewhat mechanically stable, but still not very strong, and then fired ( 800C and higher) to form the genuinely hard, rigid body.

Based on your line of inquiry, I do not think you are looking to work with ceramics.

I admit that, even with a materials science background, I came in looking for easy answers, but I am enlightened by the durometer scale information that was provided by others. It a polite reminder that we can forget things, or perhaps not have learned the critical point of language that will be helpful to others.