Modificación de un betún de Amposta por reacción de Friedel y Crafts con 4-metil-1,3-bencenodiisocianato

In this works, we have modified a bitumen from Amposta by using the Friedel and Crafts reaction with toluylene-2,4-diisocyanate in presence of aluminium trichloride, presenting as well as the characteristics of the original bitumen as the ones of the modification products. We have made technological test, aging of thin film, rheological test, thermical susceptibility and components analyses.


INTRODUCTION
7/76 asplialtic bitumen, as thermoplastic material, presents a great chemical inertia as well as an important durability, but it also has noticiable disadvantages, it is very sensitive to temperature changes.It tends to mal^e itself hard and brittle in cold weather, while in hot weather it becomes soft an fluid.Normally, the different techniques that have been used to solve these problems, have usually created new ones.For instance, by mixing the bitumen with plasticizers to increase its resistence to low temperatures, the resultant mix has less resistance to high temperatures than the original bitumen.Otherwise an increase of the brittleness at low temperatures is caused by the use of fillers to improve the high temperature resistance.
(*) A part of this work was presented at the XIX Reunion Bienal de Física y Química de Santander (Spain) and the other part to the Third International Symposium "Testing of Hydrocarbon Binders and Materials" held in Belgrade (Yugoslavia).
Los hechos anteriormente mencionados, son la prueba de la necesidad de una mejora en la calidad de los aglomerantes bituminosos que permita ampliar el marco de temperaturas en el que puedan ser aplicados, este es el objetivo principal de este trabajo.

Trabajo experimental a) La reacción
De una forma simple, la reacción entre el betún y el 4-metil-1,3-bencenodiisocianato puede representarse esquemáticamente de la siguiente forma: Thermal susceptibility of an asphaltic bitumen produces permanent deformations in flexible pavements, which are due either to static stress parking areas or to dynamic ones caused by the wheels of trucks, mainly in important falls and in very hot weather.These deformations due to dynamic stresses are spacially interesting in Spain due to its traffic circumstances: elevation axle load, high tyre pressure, a very special climatology and orography.
The above mentioned facts are a proof of the necessity of an improvement of the quality of the bituminous binder that permits to widen the temperatures range in which it can be applied, that is the main aim of this work.This modification has been made in several ways: incorporation of additives (sulphur, copolymers, rubber, ...) chemical reaction and creating a polymeric structure in the bitumen by reaction of a two components system (1,2,3).
In this work, we have modified a bitumen from Amposta, placed in the Spanish Mediterranean Coast, by using the Friedel and Crafts reaction with toluylene-2,4-diisocyanate in presence of aluminium trichloride, presenting as well the characteristics of the original bitumen as the ones of the modification products.We have made technological test, ageing of thin film, rheological test, thermical susceptibility and components analyses (4,5).

A) The reaction
In a very simplified way, the reaction between the bitumen and the toluylene-2, 4-diisocyanate can be schematically represented in the following form:
The incorporation of toluylene-2,4'diisocianate "TDI" to the asphaltic bitumen, in presence of aluminium thrichloride, was made in a reactor at 160° C, in an inert atmosphere during 18 hours.The temperature did not exceed the mentioned value to avoi the sublimation of the catalyst that occurs at 180° C.During the reaction, the stirring was constant to help the attack of the reactant to the aromatic hydrogens of the bitumen.

b) Amount of catalyst and toluylene-2, 4-diisocianate influence
When increasing the proportion of aluminium trichloride, the softening point (ring and ball) is increased, at the same time the penetration is reduced notably.The same variations can be seen by increasing the amount of TDI, although they are not so marked as the ones of catalyst (TABLE I).

Ageing in film test
It is well known that an asphaltic material increases its consistence during the mixing and continues increasing the same after its workmanship.The experience shows that the measurement of the hardening grade after that classical test of penetration, could lead to the same conceptual mistake as taking the penetration as consistence measurement.For this reason, the studied bituminous materials have been subjected to a test of ageing in thin film of 3 mm, at high temperature -the one of mixing-during a period of 5 hours; determining again the characteristics, repeating the tests that we make with the non-ageing materials.This method allow us the evaluation of the applied product consistence of the original material without any heating.This result should be the one presented in the specification.
Likewise, the alteration grade of the material can be evaluated by this method in a very approximate way, by using the increasing index of consistence or of ageing, /^ that we can define as the quotient of consistence at 60° C between the aged material, n^ and the non-aged product n;

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La medida del índice de envejecimiento que corresponde al betún de Amposta y a dos de sus productos modificados, se presenta en la Tabla II.

..,
The measuring index of ageing that corresponds to the Amposta bitumen and two of its modified products are presented in TABLE II.

Rheological properties
Asphaltic bitumens, as they are colloidal systems, have special rheological properties which permit to use them in a wide range of applications.The knowledge of such properties allow a rational classification of the same and give a criterium for the election of the most suitable material for an specific use.
In general, its behaviour can be defined in function of the following parameters: temperature, pressure, time, shear stress and shear rate.If we suppose that the first three are constant, we can obtain "consistence diagrams" that represent the shear rate in function of the shear stress that make the material flow at the mentioned shear rate (Fig. 3).En nuestra investigación y con el ánimo de obtener los diagramas reológicos más completos, hemos usado un reómetro capilar de gran exactitud (Fig. 4) que permiten una gran versatilidad de la velocidad de deformación entre 1,77 y 2.362 s-i.Las pruebas se han realizado a temperaturas entre 50 y 80^' C.
In our research and with the aim of getting the whole rheological diagram we have used a capillary rheometer of great accuracy (Fig. 4) that permits a big versatility of shear rates between 1,77 and 2.362 s-l The tests have been made at temperatures between 50 and 80'' C. Drawings 5,6 and 7 show the rheological diagrams concerning the original bitumen, the subjected to ageing in thin film process and to the one obtained in the reaction of the Amposta bitumen with TDI (1 %) and AICI^ (1 %).

Susceptibilidad térmica
La relación consistencia/temperatura es el factor que gobierna la aplicación en caliente de un betún, y por tanto es evidente la importancia de conocer la temperatura.Para obtener el adecuado valor de consistencia para una operación en particular.El conocimiento de la susceptibilidad térmica de un betún es del mayor interés y el objetivo principal de este trabajo es mejorarla.

Thermical susceptibility
Consistence/temperature ratio is the factor that governs the hot application of a bitumen, and so it is evident the importance of knov^ing the temperature to obtain the adequate consistence value for an operation in particular.The knowledge of the thermical susceptibility of a bitumen is of great interest and the main aim of this work was to improve it.
In this evaluation, we have followed two methods.The first of them by determining the penetration index parameter, calculated by the traditional monogram (Fig. 9) difference of temperature (in ° C) between the softening point and the penetration one, opposite to the value of penetration expressed in tenth of mm.

The other followed process allow us thermical susceptibility evaluation to determine the parameter named "temperature logarithmic coefficient" that results from the value slope obtained by representing in logarithmic scale the consistence (in poises) regarding the temperature in (" C).
The obtained results from capillary rheometer at different temperatures have permited to draw the lines that appear in draw 10.
Por tanto disminuye la susceptibilidad térmica en el material obtenido en la modificación de un betún y se incrementa en el proceso de envejecimiento en película delgada.También demostramos que un aumento de la cantidad de catalizador o de TDI mejora este valor.
On every line's side, there is a nunnbre that shows the value of this slope, that is to say, the temperature logarithmic coefficient.It can be checked that in thin film ageing process there is an increase of thermal susceptibility while such susceptibility decreases in the obtained products after modification.
Decreasing of thermal susceptibility in the obtained materials by modification of the original Amposta bitumen and their increase in the ageing in thin film process have been also shown by the amount of catalyst or of the TDI is increased there is an improvement of this value.

Components analysis
A bitumen is composed of a colloidal dispersion of strongly condensate molecules, the asphaltenes, in an oily phase with a less molecular weight named maltenes, that can be divided in two: flocculant or resins and peptizant component oila Once the percentage of asphaltenes, oils and resins in a determinate bituminous product is know, we may represent a point in a triangular diagram, as shown in figure 11, where points correspond to pure bitumen (point 1) and to modified products with TDI (1 %) and AICI3 (1 %) (point 2).The more a bitumen point is located to the right the higher will be its newtonian character, on the contrary, the more to the left the higher will be its viscoelastic character (see fig. 11).The components separation process is widely described in the bibliography ( 6) Para definir el parámetro llamado "coeficiente de inestabilidad coloidal" 1^ puede ser útil 7o define the parameter called "colloidal inestability coeficient", 1^, it would be useful to conocer el porcentaje de los tres componentes de un material bituminoso.Este coeficiente se define como el cociente entre el porcentaje de los asfáltenos y aceites y el de las resinas.
Hemos hecho otra clase de experimento que consiste en la adición de TDI al betún, en ausencia de catalizador, en las mismas condiciones de prueba, y hemos obtenido buenos resultados aunque no tan espectaculares como cuando el catalizador está presente.La diferencia principal es que en este caso, los productos resultantes son una mezcla y no nuevos materiales de una reacción de sustitución electrófila.
La Tabla III muestra el punto de reblandecimiento (anillo y bola), la penetración know the percentage oí the three components in a bituminous material.This coefficient defined as the quotiente between the asphaltenes and oils percentage and the one of resins: asphaltenes + oils resms The value of the colloidal inestability coefficient for the Amposta bitumen is 5,67 and for the modified product with TDI (1 %) and AICI3 (1 %) 6,69 what suggestes that an increase of such parameter implies a decreasing of thermal susceptibility and an increase in the value of the softening point.
In the same mentioned conditions for bitumen's modification by Friedel and Crafts classical reaction, it has been modified only with a catalyst, without TDI, therefore obtaining products of better thermal susceptibility.These new materials would be a consequence of Friedel and Crafts reaction in presence of AICI3, among aromatic bitumen components and their non aromatic parts, the latter acting as alkylant agents.Dealkylation, disproportion and isomerization reactions which occur with and isomerization reactions which occur with aromatic hydrocarbons substituted in presence of Lewis acid catalyst would also contribute to formation of new products (7).
We have made another kind of experiment, consisting in adding TDI to bitumen, in the same testing conditions and we have obtained good results although not so spectacular as when catalyst is present.The main difference is taht in this case, final product are a mix and not a new material from an electrophilic substitution reaction.
To classical bitumen reaction, TDI (1 %) and AICI3 (1 %), 1 cc of phosphoric acid (Brónsted acid) has been added obtaining good results but they did not improve remarkably those obtained when we only use a Lew'is catalyst.
Finally, and in order to check the ageing effect, during the reaction bitumen was heated during a period of 18 hours at reaction's temperature finding that its thermal susceptibility was worse thatn the one of the products obtained after modification.

CONCLUSIONS
In a brief way, we can mention that the most important conclusions reached today in our investigation about the modification of the bitumen comming from the Spanish Mediterranean Coast are the following: 1.The electrophilic substitution reaction among Amposta bitumen, toluylene-2, 4-diisocyanate and aluminium trichloride produces new materials with a greater softence than the original bitumen.So the thermal susceptibility is better.The improvemet of these qualities depend on the amount of catalyst or modifier agent used.
2. If the reaction is made by using only a catalyst, the above mentioned properties will be improved but, in a lower degree than when TDI mixes are used, where no valuable chemical reaction is appreciated.A Brónsted acid as co-catalyst does not improve the obtained characteristics by using only Lew'is catalyst.

To evaluate the fundamental modifications in the bitumen studied in this paper, besides the traditional technological properties (softening point, penetration) the following types of tests have been carried out:
Envejecimiento en película delgada para obtener las características mas similares a las obtenidas "in-situ".Determinación de los diagramas reológicos que definen el comportamiento del material a diferentes tensiones y temperaturas.Medida de la susceptibilidad térmica usando dos métodos diferentes y, Análisis de los componentes y su representación en un diagrama triangular que pueda proporcionar una idea de las características de los materiales estudiados.

BIBLIOGRAFÍA
Ageing of thin film test to obtain the most similar characteristics to those obtained "in situ".Determination of rheological diagrams that define the behaviour of material at different shear rates and temperatures.

Measurement of thermal susceptibility by usinng two different ways and
Components analysis and its representation in a triangular diagram that can give an idea of the characteristics of the studied materials.BIBLIOGRAPHY

TABLE III
- for the original bitumen as well as the modification products.It can be seen in the Table that when TDI (1 %) and AICI3 (1 %) are used, the thermical susceptibility is rather good, better than in all other cases.However, in all of them such characteristics are improved except in the case of thermal ageing, since there is no modification in the bitumen.