Does silicone as hard as plastic exist?

  • Thread starter Blokle
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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?
 
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  • #2
Vanadium 50
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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.
 
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As hard as PVC.
 
  • #4
Vanadium 50
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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?
 
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  • #5
Baluncore
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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.
 
  • #6
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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.
 
  • #7
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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?
 
  • #8
Baluncore
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The material injected can be a composite of materials that enhance the properties you require.
 
  • #9
phinds
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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.
 
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  • #10
phinds
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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.
 
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  • #11
jrmichler
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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:
Sample pack.jpg

They also have other sample packs.
 
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  • #12
Vanadium 50
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I don't think he means hardness. (Resistance to scratching) I think he means strength or stiffness,
 
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  • #13
russ_watters
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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?
 
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  • #14
berkeman
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  • #15
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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".
 
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  • #16
DaveE
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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.
 
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  • #17
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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...
 
  • #18
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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.
 
  • #19
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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.
 
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  • #20
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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 :)
 
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So does anybody has any suggestions for me, once I have provided additional details? Thank you.
 
  • #22
DaveE
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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.
 
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  • #23
Vanadium 50
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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.
 
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  • #24
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Vanadium 50 said:
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.
 
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  • #25
DaveE
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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.
 

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