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METHYLAL AND DIOXOLANE IN PAINT REMOVERS

Most of the paint removers offered on the European market are based on dichloro-methane.

This solvent has the advantage that it works efficiently with different types of paint : However, the suspicion that dichloromethane has carcinogenic and mutagenic effects in short term imposes the prohibition of or severe restrictions on the use of this solvent in many countries. LAMBIOTTE proposes two solvents : and with which, used simultaneously or separately, remarkably efficient paint remover formulations can be prepared. The actions of methylal- and dioxolane-based paint strippers are as fast and as visible as with dichloromethane.The two classic paint remover types, as abrasive or for rinsing, are easy to formulate with these two solvents, as they are miscible with water (methylal partially), have a low toxicity and are biodegradable.


WHY USE METHYLAL AND DIOXOLANE ?
Stripping qualities

A paint stripper works on paint in different stages :

1) Penetration of the solvent into the paint film

Facilitated diffusion of the solvent 2) Destruction of the film structure of the paint 3) Loosening of the paint film ADVANTAGES WITH METHYLAL AND DIOXOLANE
High solvent power

Exceptional solvent power of dioxolane (and of methylal) towards polyurethane, epoxy, acrylic resins (even reticulated) and towards plasticizers used in paints.

Strong polarity :

dioxolane :
  • facilitates the loosening of the film
  • assures the rupture of reticular bonds between polymer chains
Small molecular size
Because of its reduced molecular size, methylal (and dioxolane) diffuse rapidly and penetrate quite easily through all preferential routes into the paint film.
The high vapour tension of methylal accelerates the coming loose of the film (even at low temperature).

Absence of toxicity and ecotoxicity

TLV methylal : 1000 ppm
TLV dioxolane : between 300 and 600 ppm (not fixed)

Biodegradability

at concentrations up to 10 times higher than the ISO/DIS 8192 standard.

Miscibility with water

Thanks to its miscibility in water, it is possible to formulate paint removers for a specific class of paints (e.g. "latex", PVA, interior paints,)

EXAMPLES OF FORMULAS
Neutral Paint Removers

They have the advantage of being less polluting. Are used virtually universally.

Example of formulae :

D 3 : - dioxolane : 68 %
- methylal : 24 %
- Shellsol K : 4 %
- methocel 311 : 2 %
- paraffin wax : 2 % 		D 11 : - dioxolane : 56 %
- methocel 311 : 2 %
- paraffin wax : 2 %
- NMP : 40 %

These formulae are already very efficient, but they could still be improved by the addition of surfactants and synergists.

Efficiency
Time before possible removal
(in minutes)
D3
D11
  Paint on wood :
PU paint for floors
Acrylic paint for façades
Epoxy paint with 2 components
Classic alkyd paint		  
  3
10
20
5
 
  3
10
60
5
  Paint on metal :
PU paint for floors
Acrylic paint for façades
Epoxy paint with 2 components
Classic alkyd paint
  
  3
10
20
3
 
  3
5
60
3
  Paint for coachwork :  
15
 
15

Acid Paint Removers

The activity of a paint remover can be improved by the addition of formic acid and acetic acid that, by their affinity with polar surfaces, make the solvent penetrate better into the paint film.

The incorporation of these acids into a paint remover formulation, however, has some disadvantages : Example of formula : The incorporation of more water diminishes the flammability of the product.

Alkaline Paint Removers

These paint removers increase the swelling of the paint, and their efficiency is strengthened by hydrolysis of the binding agent. Triethanolamine, monoethylamine or sodium metasilicate could be substituted by KOH.

Rinsable Paint Removers ("flush off")

The miscibility of methylal and dioxolane in water is interesting for rinsable paint removers.
With the addition of potassium oleate (with ± 4 %) or soda alkylarylsulfonate the rinsing becomes easier and more efficient.

CHOICE OF THE SOLVENT QUALITY
The use of the technical qualities is preferable, all the more because the technical grade of methylal contains small quantities of methanol that increase the thickening effect of the methylcellulose (methocel or equivalent).

PRECAUTIONS DURING USE
A paint remover based on one of the above formula examples must always be used in a well ventilated place, away from every flame or source of ignition. Do not smoke.

Gloves and safety goggles should be worn.

FLAMMABILITY
Dioxolane and methylal are flammable solvents. When they are formulated with acid or alcaline additives, water and thickeners, the flash point of the mixture can change from + 10 to + 30°C according to the formulation.

Example : open cup FP : D 3 > 21°C
D 11 > 40°C

TOXICITY - ECOTOXICITY
Neither dioxolane nor methylal is considered as toxic.

TLV methylal = 1000 ppm

There is no legal exposure limit for dioxolane in occidental countries.

Neither methylal nor dioxolane inhibits the growth of the green algae Chlorella Vulgaris (AFNOR T 90-304).

BIODEGRADABILITY
Methylal and dioxolane are biodegradable in accordance with the ISO/DIS 8192 standard (measure of the inhibition of oxygen consumption of activated sludge).

LABELLING
As these products are non-toxic, there is no obligatory labelling regarding the toxicity of formulated products, due to the presence of these solvents. NMP, alkali or acids impose an appropriate labelling and packaging. Methylal and dioxolane have to be labelled in function of their flammability :

Danger symbol
F
Risk Phrase
11

Safety recommendation phrases :
S16
S 16, S 9, S 33
dioxolane
methylal

FORMULATION GUIDELINES

Paint Strippers
D 1
 D 2
 D 3
 D 4
 D 5 		ACID PAINT STRIPPER
ALCALINE PAINT STRIPPER
PAINT STRIPPER
PAINT STRIPPER
PAINT STRIPPER