Pub question: thermoplastic V's polypropelene?

[domlee]

Pub question: thermoplastic V\'s polypropelene?

In a recent post I sought, and got, some good advice on mounting a wood strake to a gunnel of a polypropelene boat . I also carried out a small repair to the boat using a polypropelene rod and a heat gun - what a task! Anyway, during the subsequent congratulatory libations - the boat stayed afloat - I was asked "What is the better material for a boat, polypropelene (e.g. Pioner) or thermoplastic (e.g. Tehri) boat?". I couldn't give an answer 'cos I'm totally ignorant of the relative merits of either. Could anyone else make an evaluation?

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[grimmy]

Re: Pub question: thermoplastic V\'s polypropelene?

hi
I can't help with the relative merits of the two boats you mention as I have no experience of either, however, I can tell you that "thermoplastic" is a generic term for a number of plastic materials of which "polypropylene" is only one.
cheers.

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[ParaHandy]

Re: Pub question: thermoplastic V\'s polypropelene?

on almost every count polyprop is a poor choice of material for a boat. it transmits moisture which isn't a good idea for use in a boat or for a fuel tank which i've seen used somewhere. to get pp to have a reasonable water transmission requires the polymer (normally a co-polymer ie has some ethylene attached to the propylene monomer) to be oriented which is very difficult in these circumstances. it also becomes brittle at low temperature. don't kick it when freezing. homopolymer pp's do have significantly better physical properties at high temperature than other thermoplastics but that's not of much use in a boat.

do you not mean thermosets? eg acrylics, poly carbonates etc. making a boat out of poly carbonates is as good as pulling the plug such is its (and other thermosets) ability to let moisture through.

or do you mean a thermoplastic composite which could be either layered or co-injected where the 'layer' makes up for lack of physical or chemical properties in pp?

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[domlee]

Re: Pub question: thermoplastic V\'s polypropelene?

Short answer to thisthred is - "I don't know! ", long answer- both types of polymer, (or is thst co-polymer/cross polymer/radia/ longitudinall polymer etc.?), suggest (acording to the ads) some sort of positive predisposition to the marine environment. The pub question evolved into the subject of "why do we not have polypropelene or thermoplastic hull & deck combination (circa 10 grand) that we can kick start the British marine ndustry into the 21st century?

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[Avocet]

Re: Pub question: thermoplastic V\'s polypropelene?

I thought "polyprop" was famous for being spectacularly inert and was used for chemical storage containers? I worked with some stuff called "Celmar" once - a polypropylene sheet with a fibrous material on the back which you could lay fibreglass up on to make it rigid. I used it for trying to make a mould for a GRP structure out of - purely because the GRP would not stick to the polyprop surface.

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[ParaHandy]

Re: Pub question: thermoplastic V\'s polypropelene?

there isn't enough rigidity in pp without re-inforcing. if you were to make a pp section thick enough (ie >4mm) to begin to have some strength, and which relieves vapour transmission difficulties, it becomes extremely difficult to manufacture. all polyolefins, thermoplastics, have very poor thermal characteristics such that whilst the outer skin can be cooled, a substantial proportion of the centre is, effectively, molten. the way you get round this is by adding nucleating agents such as talc where the impurity tends to create super-cooling sites which cool the central mass sufficiently to get it out of the mould without collapsing. however, these impurities in the polymer structure will make the end result more brittle; in some extreme cases, exceptionally brittle.

furthermore, pp shrinks on cooling. such shrinkage is nominally gone within 24 hrs but subsequent varations in temperature will cause stress and will distort the shape particularly where long and near flat panels are part of the design.

now, if you'd mentioned a polyester such as polyethylene teraphalate (PET eg coke bottle aka terylene), then you'd be on the right track .... and there's an awful lot of scrapped pet in landfill sites etc .... much better than carbon fibre imho ...


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[richardandtracy]

Re: Pub question: thermoplastic V\'s polypropelene?

...
do you not mean thermosets? eg acrylics, poly carbonates etc.
...

Err, sorry, but these are thermoplastics, most definitely not thermosets.
A thermoset is a plastic that undergoes a chemical reaction at temperature and thereafter cannot be moulded again. The most common example is Bakelite (modern versions are used in 3pin plugs & sockets).
As an aside, GRP is technically a thermoset, it's just that the reaction temperature is room temp rather than elevated to the more usual 100C +

Acrylic & PC can be moulded again, and is one of the reasons why recycling of these materials is possible (even if not done regularly).


As for the original question, what's better PP or thermoplastics. PP is a thermoplastic. A more meaningful question would be 'Which of the thermoplastics is best?' as there are so many.
My preference would be for ABS (tough, heat resistant & moisture resistant), but as it needs to be injection moulded, the tooling cost for a small dingy would be astronomical and no-one is likely to sell enough to recoup that cost.
For a lowish cost, rugged dingy, I supose PE or PP would be best. When the material degrades (as is inevitable), replace it.
For a totally disposable dingy, nothing can beat a home made plywood one.

Regards

Richard.


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[ParaHandy]

Re: Pub question: thermoplastic V\'s polypropelene?

fair point ... practically they are very difficult to recover which is why i put them in that category.

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[grimmy]

Re: Pub question: thermoplastic V\'s polypropelene?

The amount of moisture able to pass through polypropylene would be negligable in boat terms, millions of times more falls out of the sky almost every week in Britain. I believe the Topper dingy is moulded from polypropylene and there are thousands of those in everyday use. Virtually all thermoplastics degrade with UV light and so become brittle over time when exposed to sunlight. I would have thought that a much more important factor in the longevity of boats made from thermoplastics was the degree of UV stabilisation rather than the actual material.
However, it is unlikely that the ordinary punter would be able to get hold of such information.

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[ex-Gladys]

Re: Pub question: thermoplastic V\'s polypropelene?

Topper is ABS

<hr width=100% size=1>Larry Botheras

Anderson 26 "Amber"

 

[rex_seadog]

Re: Pub question: thermoplastic V\'s polypropelene?

Beg to differ but the Topper is injection mouded polypropylene. Check out their website.

As an aside see my posting 'Tales of a Topper'.

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