So...Since there isn't anything really useful being offered in this thread, I'll add why fiber fillers are added to thermoplastics. Typically, its for strength purposes. For instance, on an outside rearview mirror on your car or truck, the mounting bracket used to be made from Aluminum or magnesium (some still are). However, plastic parts are generally less expensive to produce, so the mounting brackets have been moving toward that material. On a small car mirror, that is great. On a large truck mirror (think F150) the plastic isn't stiff or strong enough to pass government testing. The image is blurry (there is a spec in the FMVSS for image stability) and they may fall off the vehicle upon impact or in a car wash (which will be a customer issue...Think hitting your garage door while pulling in kind of impact). So, the resin suppliers put their thinking caps on, and load up the mixture with tiny glass fibers. Or Aramid, or Carbon, etc. Glass is most common, because its least expensive. The highest glass concentration I've ever seen used is a 60% glass filled plastic on a Toyota Mirror. For some engineering stuff...
A generic, picked at random Polypropylene has a tensile strength of 4200 psi. The material is RheTech Polypropylene CC20P100-00. Its a calcium carbonate filled material...the Calcium is added to help control sink (polypropylene has a coefficient of expansion so they add stuff to help control that property). If you take the same material (RheTech Polypropylene G10P100-00), and add just 10% glass fiber to it, the Tensile strength increases to 7100 psi. Stiffness and hardness also increase.
Interesting to note...A polypro material with aramid fibers (RTP 100 AR 15)... Tensile strength is 5200 psi, but the impact resistance is higher (so its "tougher" i.e. less brittle).
Now...this data is applicable to thermoplastics, you can see all the specs at
www.ulprospector.com and register for an account...I don't know much about the molding of rubber...Its possible that the kevlar was added to add some resistance to tearing (as
@bobthetj03 has experienced) but it seems that that resistance may come at a cost of some flexibility...which opens the debate to usable vs total flex again.
Again...I'm applying knowledge of thermoplastics to a thermoset material (rubber) so whether the additive
I wasn’t trying to be critical, I just don’t see any practical reason for the addition of Kevlar
So...Since there isn't anything really useful being offered in this thread, I'll add why fiber fillers are added to thermoplastics. Typically, its for strength purposes. For instance, on an outside rearview mirror on your car or truck, the mounting bracket used to be made from Aluminum or magnesium (some still are). However, plastic parts are generally less expensive to produce, so the mounting brackets have been moving toward that material. On a small car mirror, that is great. On a large truck mirror (think F150) the plastic isn't stiff or strong enough to pass government testing. The image is blurry (there is a spec in the FMVSS for image stability) and they may fall off the vehicle upon impact or in a car wash (which will be a customer issue...Think hitting your garage door while pulling in kind of impact). So, the resin suppliers put their thinking caps on, and load up the mixture with tiny glass fibers. Or Aramid, or Carbon, etc. Glass is most common, because its least expensive. The highest glass concentration I've ever seen used is a 60% glass filled plastic on a Toyota Mirror. For some engineering stuff...
A generic, picked at random Polypropylene has a tensile strength of 4200 psi. The material is RheTech Polypropylene CC20P100-00. Its a calcium carbonate filled material...the Calcium is added to help control sink (polypropylene has a coefficient of expansion so they add stuff to help control that property). If you take the same material (RheTech Polypropylene G10P100-00), and add just 10% glass fiber to it, the Tensile strength increases to 7100 psi. Stiffness and hardness also increase.
Interesting to note...A polypro material with aramid fibers (RTP 100 AR 15)... Tensile strength is 5200 psi, but the impact resistance is higher (so its "tougher" i.e. less brittle).
Now...this data is applicable to thermoplastics, you can see all the specs at
www.ulprospector.com and register for an account...I don't know much about the molding of rubber...Its possible that the kevlar was added to add some resistance to tearing (as
@bobthetj03 has experienced) but it seems that that resistance may come at a cost of some flexibility...which opens the debate to usable vs total flex again.
Again...I'm applying knowledge of thermoplastics to a thermoset material (rubber) so whether the additive reacts the same...I cannot say for sure.
The more you know...
I wasn’t trying to be critical, I just don’t see how adding Kevlar would benefit the product.
Yes Kevlar has high tensile strength but poor abrasion resistance.
I also understand why fibers are added to plastics or concrete but adding a fiber that does not resist abrasion well does not really add anything in a torsion application, does it?