Oxidative recycling of crosslinked polymers

Recycling cross-linked polymers unlike thermoplastic polymers poses serious problems. The ozonation of liquid phase cross-linked EVA waste can provide, by decreasing the molecular weights of the polymer fragments and their peroxidation, a first solution. The thus modified cross-linked EVA can be incorporated and recycled into virgin polymer formulations, improving the performance of road bitumens, or serving as bases for the preparation of paint emulsions.

In addition to this and more fundamentally, the studies of radical initiators generated on the ozonized EVA allowed to evaluate their reactive capacity with respect to vinyl monomers, to assess the actual behavior of the macroinitiator in the grafting medium and show the effects of medium viscosity on recombination reactions of free radicals.

Gel permeation chromatography makes it possible to estimate the number of peroxide functions per EVA chain. These are essentially hydroperoxides easily dosed by a sensor of free radicals of the genus DPPH which does not break down the peroxides.

Various ozonized EVA materials grafted with polystyrene have been manufactured. They have remarkable accounting properties and allow the disappearance of phase segregations in EVA / polystyrene mixtures.

This work has been extended to crosslinked polyethylene and polypropylene. The results obtained are very convincing.

Alkyds and inks

The printing ink composition essentially incorporates compounds derived from petroleum.

Due to their structures and properties similar to mineral oils, vegetable oils are suitable for use in the printing industry, in this case in offset fatty inks. The objective of this study was therefore the development of printing ink varnish based on sunflower or rapeseed vegetable oil never used in this type of application.

The introduction of vegetable oils or derivatives can be at two levels in varnishes :

• on the one hand, replacing the mineral oils widely used as diluent, by methyl esters of fatty acids derived from vegetable triglycerides.
• on the other hand by substituting the conventional alkyd resins with new-type alkyds produced from rapeseed oil and sunflower oil.

The synthesized alkyds are initially characterized chemically and rheologically. In addition, they must meet certain printing ink requirements for compatibility with thinner and hard resin, which are other materials needed to make a good varnish. The prepared varnishes must have characteristics very close to the standards imposed on certain parameters, such as viscosity or tack, for example.

Varnishes meeting all selection criteria are then pigmented to obtain ink formulations suitable for printing. After rheological characterization of these ink compositions, all the printability tests are performed on a sheet machine, and in heatset in order to evaluate the behaviors in real conditions.

It is then possible to determine if a formulation has all the required properties such as drying, gloss, dot accuracy or no smearing.

The second phase of this work consists of an in-depth fundamental study of still poorly understood interactions between paper and variable ink porosity printing media.Advanced spectroscopic techniques are used for this purpose. The scientific knowledge of ink-paper chemical interactions, relaying empirical knowledge, made it possible to determine the different parameters responsible for quality printing on the one hand, and to better control deinking operations during recycling on the other hand.

Polyester resins

The work developed follows those carried out on the same theme, described above. It involves studying and rationalizing the formulation and implementation of different polyester resins in the manufacture of boat hulls.

They led to the development of a method for monitoring the polymerization reaction implemented on the production lines and developed in terms of technological innovations.

Collagen and ecological leathers

The flexibility and strength of today’s leather is the result of trivalent chromium. The crosslinking of collagen in water by chromium salts is therefore the essential basis of the leather industry. It is also, by the excessive releases of chromium in the environment, its essential problem.

The experience acquired elsewhere on other types of fibers allowed us to approach this problem from an original angle and to propose some effective solutions. Ongoing industrialization should enable the hides and skins industry to progressively gain the enviable rank of clean technology.

The first studies focused on how to reduce the aging time of chrome leathers, in fact to improve the kinetics of chromium fixation in the collagen network.

A rise in temperature in the tanning operation with precise pH control reduced the rest time of tanned skins to less than 24 hours before finishing operations. The obvious economic gain is doubled by more than a very small release of chromium.

This work led to the development of the CrAB (Chrome Auto Basifier) ​​process, which allows, by pre-tanning followed by tanning using particular masking agents accompanied by pH control and control the temperature, significantly reduce chromium releases that go from a few grams per liter to a few milligrams to fall below the most stringent release standards.

These results have been further optimized by a better understanding of the fundamental mechanisms that govern these operations. Electron microscopy has enabled us to establish a new characteristic of chrome leathers: the crosslinking coefficient, which is defined as the ratio of the number of connections between the fibrils on the number of fibrils considered.

The conditions of dyeing and degreasing being perfectly controlled, special attention was also given to peeling operations and the possible substitution of sulphides and lime by glycolic acid, enzymes and carbon dioxide.

Moreover, the work carried out on methanesulfonic acid shows a surprising 

Paper pulps from annual plants

The continuing increase in the amount of paper consumed worldwide, coupled with the difficulty of accessing primary or secondary forests and the chlorine pollution problems of most pulp mills, has made the development of Chemical pulps of annual plants, especially cereal straws (wheat, barley, paper sorghum …) and bagasse of sugar plants (sugar cane, sugar sorghum) is unavoidable.

The cooking processes studied were of the soda and soda / anthraquinone type.

The paper pulp obtained is separated from the black liquors studied elsewhere, in terms of energy potential and sources of sulfur-free lignins with little condensation.

The chemical pulps of paper and sugar sorghums obtained according to these two types of cooking, are comparable to softwood pulps, whereas the pulps of wheat straw, barley, bagasse of sugar cane, have properties close to the hardwood pulp. 

They allow, in mixture, obtaining paper ranges identical to those obtained from wood.

Lignins : extraction and oxidation 

The first work done on the subject dealt with improving the digestibility of plant fibers by oxidative destructuring of the parietal polymers by ozone.

The experience acquired was used to develop an original process for producing vanillin from organosolves lignins from the Organocell process, selectively oxidized by ozone in heterogeneous gas / liquid / solid medium.

This type of more or less oxidized lignin was then demethylated and functionalized so as to use it as a seed coating binder and phytosanitary formulation base.

It was logical, after having been interested in the pre-extraction of hemicelluloses (4-3-Po-1-3), and showed the remarkable potential of the method, to be interested in the lignins present in the black papermaking liquors.

The black liquors obtained are fractionated by precipitation of their various organic constituents to the cooking salts which must be recaustified.

Lignins are characterized in terms of monomeric composition, and degree of 13C-NMR polymerization using DEPT pulse sequences and electrospray mass spectrometry.

A final comparative mass balance is established, which makes it possible to discuss the possible valorization of these polymers, other than thermal, notably as an active or semi-active charge of polyurethanes or polyesters in various original applications, ranging from the manufacture of new insulators to the protection Plant.