Composite Nylon Substitute 2

[RanLwr]

Does anyone know of a substitute for a Glass filled Nylon that would have greater strength performance
We use Nylon 6 with 25% glass filled.
We achieve 160 MPa Tensile Strength
and
7600 MPa Flexural Modulus

I would like to increase the flexural modulus without giving up the tensile strength.
Thanks

 

[RPstress]

Sounds like short fiber reinforced (possibly injection molded; might be compression molded?).

I take it that you've looked at the obvious stuff like inreasing glass content a bit or even using different glass or carbon. Why were these inappropriate? What are your limitations?

 

[RanLwr]

Thank you for your response.
It is short fiber glass filled Nylon 6 25% filled injection molded. General Commercial grade.
I actually misstated my goal, I actually would like to decrease the flexural modulus value without giving up tensile or impact.
We have tried more glass and achieved very high results in tensile and flex mod. but it was to brittle.
The Tensile Strength And Flex Modulus goes up concurrently.
You mentioned carbon fiber, this is something we have not explored.
Would there be some advantage in a reduction of flex mod. there?
Thanks Again

 

[RPstress]

Decrease in flex modulus with no loss of strength or toughness...a tough one! E-glass fibre at 70 GPa (10 Msi) is about as flexible as reinforcement fibres get and has good strength (maybe 2800 MPa/400 ksi). Natural fibres such as flax from

http://www.compositesevolution.com/

have a claimed E of about 50 GPa a claimed strength of about 500 MPa so will be a bit weak and and will also vary a lot, not to mention being affected by moisture ingress, but it should make a more flexible material.

Just reducing the percentage of glass will decrease both stiffness and strength (roughly pro rata the %) but may well increase toughness. Using something like C-glass (more corrosion resistant than E-glass and slightly lower modulus) might give a small reduction in both stiffness and strength. Possibly a pure silica glass might help; you could try contacting ASGLAWO (

http://www.asglawo.de/).

Pure silica should be about 10% lower modulus and similar strength (E-glass is mostly silica but has a load of other oxides in it).

Adding ordinary carbon will increase stiffness and strength markedly but will probably decrease toughness a bit. Ultra-low modulus (ULM) carbon such as XN-05 (from NGF, see

http://www31.ocn.ne.jp/~ngf/english/product/img/p1/pdf/xnfiber.pdf

(

http://www31.ocn.ne.jp/~ngf/english/))

will be more flexible than E-glass but probably a bit weak and may well be expensive. It will also be somewhat conductive (depends on details of your use). MCA (Mitsubishi Chemical America) also do some ULM carbon (e.g.,

http://www.mitsubishichemical.com/DataSheets/CarbonFiber/PD K223Y1.pdf—again

looks a bit weak cf. glass).

Do you need both the decrease in bending modulus and maintenance of strength and toughness in the same direction? There might be practical ways to control fibre directions in the final part. Since it's injection molded there's presumably some fiber directionalising in the product anyway. Decreasing modulus and maintaining strength are usually not very compatible, but if you need the properties in different directions something might be possible just by choosing the directionality of the fibers in the finished product.

Changing the fibre length and/or diameter is also fairly doable (glass diameters range from AA to U, 1 micrometer to about 25). However, changes to modulus will also change strength in the same direction, although not the same amount. It also will change the injection molding characteristics somewhat. Changing length should affect strength more than modulus and decreasing diameter should increase toughness for the same Vf. A lot depends on the fiber length/diamter ratio and how much the short fibres are deformed, or if they are too short and fat to do so.

Fibers are what contribute most to the strength and stiffness, even glass at 25% Vf; but changing resin will also have an effect, and at 75% resin volume it might be significant. However, there aren't many resins to choose from with a lower modulus than Nylon (all polymers tend to be very similar). Possibly polypropylene (PP), though it won't help much and may well weaken the material even if it's manufacturable. Changing to something like PA-66 would give a small increase in strength cf. PA-6 and might permit a reduction in glass and therefore stiffness for the same strength. These changes will affect manufacture quite a lot.

Hope there's ome foood for thought there. More detail on your use would probably help. Please note that I'm not an injection molding specialist.

 

[RanLwr]

Thank You for your time and expertise.
This has definitely given us some new perspectives on the matter.
The part we are trying to produce replaces a zinc die cast part.
It is in a residential window, and it is the pivot bar that allows the window to tilt out.
The dimension is 5/32" x 5/16", and the entire weight of the window rests upon it.
The suggestions and ideas you gave will be very helpful and for someone who is not an injection molder you are very knowledgeable in the field
of thermoplastic composites.

The information on glass type, size, and direction may be exactly what we are needing.
This type of information is not given out very freely by our material suppliers.
We are also looking at a polycarbonate Carbon Glass Composite.

Thanks Again for your time and help.

 

[RPstress]

That sounds as if failure could be quite serious: a fairly heavy structure with a breakable glass pane and people's heads and arms nearby.

For your alternative material suggestion, nothing wrong with polycarbonate as a matrix. Nice and tough and should retain toughness down to a lower temperature than Nylon, plus quite strong (a little bit less than Nylon), but I have no data on how well it should stick to fibres, although the carbon composite transverse flexural strength is sound (I don't have any interlaminar shear data which can warn of a low interfacial fiber strength if it's low). A mix of glass and carbon, a 'hybrid,' of short fibres is not something that I'm at all familiar with. Rumour has it that you might get some synergy with strength from the carbon and flexibility/toughness from the glass.

Good luck and hoping you don't need it.

 

[RanLwr]

Thanks for taking the time to share your expertise.
I'm certain it will be of value in our planning and design.

 

[RPstress]

Just noticed the Polymer engineering forum (forum334). (In fact it just appeared in my Materials Engineers sub-section—thanks someone.) Some of the regulars there know a lot about injection molding and may well know short fiber materials a lot better than I do.

 

[RanLwr]

Great Thanks A Lot!