glass or mica added to pp failing on molded panelsHELP

[jackp55]

We are having panels molded for us as decking on marine docks that are 24" x 48" x 1.2" deep and have strengthening ribs. The part weighs 6 pounds and the life is 10 years. The color is light fixture gray and we add anti UV and anti static agents.

The material is polypropylene.

The panels are set on frames with a 24 inch span.

We just implemented two simple new tests as pass/fail criteria:
1. Static Test. With a 200 pound weight in the center of the span the end of the panel (36" away) flexes or raises .5 inch or less. The reason for this to minimize stress on a separate fastening clip. We could get by without this stiffness requirement.
2. Jump Test: We simply jump up and down with a 200 pound person on the panel in the center of the span to try to break it.

We molded the panels with PP and no glass in development and found them to be too flexible and put too much stress on the fastener clips.

We then molded panels with 20% glass added which passed both tests but the fibers started working themselves out causing slivers in feet and hands after 2 years in the field.

We switched from glass additive to mica at 20%. These panels are too brittle and fail the jump test.

We tried molding a sample with 18% mica and it failed the jump test.

Our molder is in Shanghai China and he has been selecting the materials so far based on my input. I asked him to select a PP copolymer used to make auto battery cases but have no idea what specific material was used because of a language barrier.

I need help. I originally picked PP because our competitors used it and thought it to be good material to resist gasoline spills. Now I am thinking I should pick ABS or another material. Please help with suggestions.

 

[patprimmer]

Nylon might be a good choice if it will stand the cost.

Can yoy make the ribs deeper.

Do the cracks start at a sharp corner.

Is there any moulded in stress. PP is very prone to differential shrinkage which can create large stresses, especially near the gate.

If it is thin section and a long flow path, the moulder is probably using a very high MFI base resin and that can substantially reduce impact strength and elongation at break.

If it is stiffened by glass fibre, the quality of the glas re aspect ratio and surface treatment can be very important re obtaining maximum properties.

Mica is stronger overall than talk, but not nearly so strong as fibre in the flow direction. Mica might have a strength advantage across the flow, depending on quite a few factors.

Regards
Pat
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[Demon3]

A filler that improves strength and modulus of PP while retaining or improving your impact resistance is Halloysite. There are papers proving that. The particles have high aspect ratio so you get strength and modulus but because they are only 1-2 microns long and easy to disperse, you don't lose any impact. In PP impact improves. Adding just 1 weight% gives +20% modulus and strength. It has been used commercially in large floor parts. Note: I work for a company that sells this material.

Polyolefins are not good against gasoline spills because chemically, gasoline is just about identical to PE and PP so they will swell.

ABS could be a better choice for that but it's not great against UV.

Nylon is strong, works well with fillers and great against gasoline because it is much more polar than gasoline so the two do not interact.

I would expect this to work with PP (or HDPE) and the right filler. Nylon is more expensive as Pat said but would work well.

Chris DeArmitt PhD FRSC CChem