Thoughts, Help and Ideas on this topic appreciated

I'm starting out to build a number of kits and my model shop suggested using D-Limonene as the way to go.

 The chemist in me perked up his ears as mono-terpenes / terpenoids are natural products and typically non- to low toxicity. Think menthol, peppermint oil, eucalyptus oil, camphor, pinene (from pine oil, rosemary and the like) etc. etc., many having uses as non-prescription health remedies. D-Limonene as its name suggests, is found in citrus peel, sour oranges being a significant source. I think that my home made Marmalade must be loaded with the stuff, as well as in good Sauternes perhaps?

That means I'm totally relaxed about its health issues, acute and chronic; we face many more nasties out there every day so on to using it as a glue and this is where I'd appreciate help. It's straight forward to glue PS sheet together, the bunker on my Terrier was done that way but what about fixing long thin sections or smaller parts in kits?

One thing I'm experimenting with is expended PS foam dissolved in minimum amount of Limonene, quite interesting to watch a big lump collapse into a tacky goo. Is it better to use this or to paint on the neat solvent?

Hi Colin,

I've not herd of this alternative for joining styrene kits together, but am very interested in your comments and observations once you have had a chance to try it out. I am a reluctant, but frequent user of solvent adhesives for plasticard and plastic kits and one of the most important attributes of an effective plastic adhesive for me, is obtaining a rapid bond, otherwise scratch and kit builds take far too long.

Bon courage with your experiments and I look forward to the results in due course.

I'm off to lay some slates now!

Bill

Limonene was recommended to me by a skilled modeller at a demonstration - but only for certain uses…………….. :roll:

Apparently, this particularl modeller (who's name escapes me at this moment), used Plastic Weld and Mek Pak for glueing hefty bits of styrene together when he wanted an instant, strong bond.

He used limonene in situations where he wanted a slower cure with an element of "adjustability", on thin styrene material when the brutal Mek Pak type products were likely to distort or even eat the glued material and almost without exception, when fitting window frames and their glazing.

Apparently offers a good bond but gently in every aspect ………………

Hhmm,interesting.
D

It is useful when laminating poly surfaces together as it doesn't evaporate quickly and allows the surfaces to bond smoothly without bubbling as happens sometimes with more traditional liquid cements. It was useful when putting together layers for coaches done on the Silhouette cutter. Deluxe materials do a 10 second solvent that has a low odour and I also use this at times although it is not a limonene based product.

Needs Must!

As reported earlier, confined to "barracks" as I am by both COVID and a Moon Boot, I was keen to get my kits underway but have no easy access to a shop for suitable adhesive.

I figured my jar of limonene must be useful somehow and picking up on an earlier tip from Nigel, I decided to "play around" at formulating a limonene based adhesive. With ready supply of old CD covers to hand for clear PS, I snipped some up and dissolved it adding sufficient to get a very viscous goo. (Probably similar to Golden Syrup).

It turns out that this thick, it can be used much like rubber based contact adhesives. Apply to one surface, pull away (making good and spots of shortfall) then recombine. Of course the grab is not as immediate as the rubber product but with some help from a few tiny strategic spots of CA for hold, the combined effect is very good and quick enough to be practical for further work while the join is setting stronger with time.

 

Hi Colin,

The toxicologist in me says use with caution. Just because it's natural doesn't mean it's safe. Hypersensitivity reactions (skin) and possible effects on liver drug metabolism have been reported. Concentrations used in food and cosmetics are much lower than found in solvents. As usual, well ventilated work area, gloves, eye protection and dispose of properly. 

Nigel

Thanks Nigel,

No need to worry unduly, while I'd agree that being natural is no reason to be complacent about a chemical, I get greater exposure from my home made marmalade! Orange peel has ~1% limonene content so my morning breakfast treat exposes me to perhaps 20 times the level I'd get from my glue where I'm using a few milligrams at most at any time, containing not more than 20% solvent. My normal hand cream has Orange peel extract among other things etc.

 Besides, as an ex- research chemist I know about the various risks out there and how to work with them. I spent far too many hours in front of a fume cupboard handling nasty things. If limonene was going to irritate me I'd know by now.

Hi Colin,

 Limonene (or more specifically it's hydroperoxides) is becoming a recommended as a routine patch test in individuals with contact allergy to perfumes and fragrances. Contact allergy can appear almost immediately or after many years of exposure. I just checked Pubmed (limonene and allergy). From one article in 2014 (Allergy to oxidized limonene and linalool is frequent in the UK. Br. J. Dermatol., 2014 Aug;171(2):292-7) there is a 5% positivity to skin testing in patients attending  dermatology departments. That's high.

 The incidence observed is comparable to other studies. GRAS designation does not mean that it is totally safe. It readily oxidizes on exposure to air, the products are potent sensitizing agents.Not everybody has contact dermatitis, but the incidence in those that do is a definite warning to take care when using it.

 BTW, that toast is probably much more dangerous than the marmalade. Jury is still out on this, but toasting that bread generates acrylamide, regarded by most authorities as a potential carcinogen. Many carcinogens have cumulative effects, so a short-term high dose study in animals may be reflected in a much lower but prolonged exposure in humans. 

Feels like I'm back at work!

Nigel

There is a danger here of demonising perfectly acceptable and manageable levels of risks of limonene in the minds of the average modeller and breakfast diner.

 Orange oil is widely used in aromatherapy and hand creams so surely any serious widespread risks from longer term low level exposure would have become apparent by now. Wheat and its related cereals cause severe allegries in ~1% of populations but we've learnt to manage and live with them

 According to Prof. WikiP … "Most reported cases of (limonene) irritation have involved long-term industrial exposure to the pure compound" 

People are very poor at assessing the risks they face, it's one of the first things you're taught on workplace safety courses. Think driving a car, COVID, both of which people incorrectly believe they can accurately risk estimate. They tend to overreact to minor risks which they cannot self-estimate and downplay others which they think they can.

 Let's maintain perspective on this, the hazards from many other glues and modelling activities (e.g. soldering, sawing MDF) are probably much higher than both using limonene and the occasional slice of homemade toast and marmalade. Take care breakfast's up.

(SWMBO took a bite between kitchen and office! Bread hers, marmalade mine :cool:) 
 

Hi Colin,

Right at the beginning you did ask for thoughts on this topic. The issue with all chemicals is deciding what the risk benefit is. Yes, long term exposures to high concentrations of any chemical has more risk than short term exposure to low concentrations. Looking at source documentation (rather than Wiki) it is clear that the concentrations found in fragrances and detergents used by end use consumers is enough to elicit hypersensitivity (which is significantly influenced by the genetic profile of the individual).

My thoughts are that this compound may be safer than conventional plastic solvents but has a low but real capability of inducing hypersensitivity if appropriate safety measures are not taken. Looking at the bottle of "Goo Gone" remover spray in the cleaning cupboard it says it contains terpenes from oranges, 40% VOC and somewhere between 0.1 - 1.0% terpenes. "Avoid contact with eyes and prolonged skin exposure". The latter is because of the hypersensitivity issues. The SDS specifically states that it may cause allergic skin reactions. Caveat emptor.

I brought up toast as an illustration that everyday items have a low but tangible risk. Barbecued meat (high temperature) or grilled bacon (especially nitrite preserved) is another (nitrosamine formation, guidelines are not more than once a week). Still doesn't stop me from enjoying a full Monty, but only a couple of times a year. No marmalade unfortunately as I cannot stand the taste. Must be the terpenes.

As modelers we use lots of chemicals, many of which have known safety issues. I would recommend looking at the SDS if at all unsure about the risk. I am always struck by the statement on many items here: "Known to be a carcinogen in the state of California". Thank goodness I live in the state of Virginia. Perfectly safe here then.

I have often wondered about outgassing of terpenes following solvent welding of plastic. 

Nigel