Microemulsions in water soluble sachets

H.B. Dawson

As increasing pressure is put on companies to reduce the impact that their business has on
the environment, Enviroquest launch new innovative technology to help address the problem.

During the mid 1990's it became increasingly obvious that governments would begin the process of introducing a range of stringent measures aimed at reducing significantly the levels of packaging waste generated by the chemicals industry. Moreover, it was clear at an early stage that these measures would not simply result in a series of administrative nightmares to the industry but rather there would, in addition to these issues, be a real and very significant financial penalty to pay.

These measures are now beginning to ' bite' with companies of turnover greater than £2m per annum already being forced to pay a 'tax' for recovery, decontamination & recycling of these containers. It is also worth noting that until recently the turnover threshold at which point this cost' kicked in' was £4m per annum so we can clearly see the direction in which we are heading.

During the same period of time we have seen the environmental pressures placed on our industry increase at an alarming rate to the point where it seems that every month there is another newspaper article or TV programme in which the timber treatment industry is portrayed as irresponsible, uncaring and uninformed with respect to the impact that our operations are having on the environment.

Whilst many of the criticisms leveled at our industry are clearly based on an exaggeration of the known facts coupled to journalistic 'scare mongering', we cannot hide from the fact that public perception of the industry is at an all time low and falling. These stark realities were very clearly outlined and explained by a number of eminent speakers at our bi-ennial BWPDA Conference in Derby during June. These presentations whilst thought provoking and very interesting were nevertheless extremely painful to listen to.

Given this background, Enviroquest in 1995, initiated work on the following three distinct programmes of research within our timber preservation section:

(a) development of fully water based microemulsion formulations in which the toxicological and environmental impact of the co-formulants was reduced to a minimum;

(b) examination of new active ingredient molecules such that by combination of increased biological efficacy and reduced toxicity we could develop formulations in which the relative toxicological and environmental risk factors could be reduced to a minimum, and

(c) examination of the use of water soluble films in a manner which would allow us to very significantly reduce or even remove completely the impact that waste packaging has on our environment.

It is pleasing to note that we have achieved a great deal of success within all of these three programmes, however, it is the development of packaging systems based on water soluble films which we now want to discuss.

Enviroquest were proud to be able to announce at this years BWPDA Conference in Derby the introduction of their new Water Soluble Sachet (WSS) technology accompanied by a range of new products for use in the remedial timber treatment sector.

UNIQUE ADVANCED TECHNOLOGY
• Minimises Waste
• Minimises Operator Exposure
• Minimises Environmental Impact
• Minimises Logistics

The fundamental design of these products is based upon placement of a range of water internal microemulsion systems inside a sealed envelope of a water soluble film. This sachet is
then contained within an outer pvc bag which is to protect the sachet from accidental exposure to water. Typical sachet sizes are 125-167 mis with one sachet being used to prepare 25 litres of spray dilution using instructions shown diagrammatically below.

The development of formulations to be incorporated in to the sachet systems used as a starting point our current, well established, microemulsion technology developed over a number of years based on fully water based systems containing no solvents whatsoever. However, given the nature of the water soluble film, we needed to prepare oil external microemulsions and the use of phase  diagrams  based  on [Pcos]m, [Ph/s]m and [Paq]m relationships coupled to the use of conductivity profiling, were needed to allow us to develop formulations having the following characteristics:

(a) good stability at high (54°C) and low temperatures (0°C);
(b) chemical and mechanical stability when exposed to freeze thaw cycling at -20°C;
(c) high active ingredient contents up to 35% w/w to give a small sachet size;
(d) excellent spontaneity to produce water external microemulsions once the contents were in contact with water;
(e) high levels of compatibility with the water soluble films (absence of any solvents);
(f) a fully biodegradable surfactant system giving high stability in the 'in use' dilutions.

Once we had successfully developed formulations with the required characteristics we then needed to turn our attention to the stability of the sachets themselves and as with the formulations we needed to examine the effects of high and low temperature storage on a wide range of properties which
included:

(a) Compression Testing which looked at the applied weight needed to cause fracture of the sachet;

(b) Shock Fracture Testing which looked at the effects of dropping either the individual sachets or boxes containing sachets onto concrete from heights up to 3 metres;

 (c) Dissolution characteristics which looked at the time needed to fully dissolve the sachet once added to water;

(d) Spray characteristics which examined the rate of spraying from a conventional pump system used for treatment of timbers with a conventional product used as control;

(e) Appearance of film to ensure that there was no deterioration or change in the product following storage.

In both tests the storage regime consisted of 54°C (2 week), 40°C (8 week), 35°C (12 week), UK Ambient (2 years), 0°C (6 months) and freeze thaw cycling between -20°C and ambient (5x) and results are given in Tables 1 and 2 below.

Note: '1' Spray time for normal fluid, ' 2' Spray time for sachet fluid
The results clearly demonstrate a very high level of stability for both the sachet and the microemulsions contained in them.
Using this technology we have developed the following range of products:

(a) Insecticide based on 20.0% w/w permethrin in a 125 ml sachet.
(b) Insecticide based on 3.0% w/w Flurox** in a 135 ml sachet.
(c) Fungicide based on 25.3% w/w propiconazole and 8.4% w/w IPBC in a 167 ml sachet.
(d) Masonry Biocide based in 15.0% w/w IPBC in a 167 ml sachet.

All products will be supplied in a double skinned box with an internal divider to allow the sachets to be individually packed. The box is designed so that all products will be in the same size of box and a comparison in specifications vs conventional boxes containing 6-12 bottles is given in Table 3
opposite.

The benefits to be gained by switching to WSS technology are numerous indeed and would include:

• Reduction in storage space required

• Reduction in transport required

• Removal of problems associated with lifting heavy weights

• No variation in dilution concentrations with dilutions easily and consistently prepared

• Significant reductions in plastic waste

• Significant reductions in cardboard waste

• No exposure of operators to concentrated pesticides

• No release of pesticides into the environment from 'empty' containers etc.

With respect to environmental impact data, Table 4 below gives comparisons of the impact from pesticides supplied in a 12 x 1 litre bottle format against the equivalent in a sachet format using figures based on the current levels of use in the UK remedial market.

We believe that this new innovative technology represents a major breakthrough for our industry and gives us the opportunity to respond to the 'critics' in a very positive manner when they claim that we are not aware or concerned about the effect our products have on the environment.

NOTE
*based on the analysis residual pesticide from samples of supposed empty and washed out bottles.

** Flurox is a registered product of Janssen Pharmaceutica and is supplied in the UK by Sovereign Chemicals Limited.

Table 1

Table 2
Stability of Water Soluble Sachets

Specifications for Packed Product

Environmental Impact - UK Remedial Market