Patent Publication Number: US-2023136196-A1

Title: Polymerisation station for grafting a bioactive coating

Description:
The present invention relates to a polymerization station and to a method for grafting a bioactive polymer, such as PolyNaSS, onto an article, in particular a polymer or ceramic article. The polymerization station comprises a reactor comprising a vessel for receiving the articles for their oxidation and grafting, a cover which is mounted on the vessel in a fluid-tight manner, an inlet for at least partially filling the vessel in order to immerse the articles, and a discharge for draining the vessel. 
     This type of reactor is known from the prior art, in particular for carrying out small and medium scale experiments of the synthesis type in laboratories. 
     The objective of the invention is to carry out the oxidation and grafting on an industrial scale, i.e. in a repeatable and guaranteed manner in large quantities and at a rapid rate, which is not the case in the laboratory. 
     To this end, the invention proposes an oxidation and grafting method for grafting a bioactive polymer, such as PolyNaSS, onto an article, in particular a polymer or ceramic article, the method comprising a step for oxidation by ozonation and a step for grafting by radical polymerization in a polymerization station comprising a first reactor, the method being characterized in that the two steps for oxidation and grafting are carried out consecutively in different solutions in the reactor of the polymerization station. 
    
    
     In accordance with one embodiment of the invention, the first reactor comprises a first vessel for receiving the articles for their oxidation and grafting, a first cover which is mounted on the first vessel in a fluid-tight manner, an inlet for at least partially filling the first vessel in order to immerse the articles, a first drain outlet for draining the first vessel, an ozone inlet for bubbling ozone into the first vessel with the aim of oxidizing the surface of the articles immersed in the water, and a monomer solution inlet for at least partially filling the first vessel with monomer solution in order to immerse the articles in the monomer solution. 
     In accordance with a very important feature of the invention, the step for grafting by polymerization comprises preparing an aqueous solution of monomer in a second reactor of the polymerization station connected in series upstream of the first reactor in order to be able to decant the monomer solution from the second reactor into the first reactor. The two reactors may be maintained at an overpressure by injecting an inert gas such as argon. Advantageously, the step for oxidation by ozonation comprises at least partially filling the first reactor with water deriving from the second reactor. 
     Preferably, the first tank comprises a first double wall in a manner such as to define a peripheral circuit for circulating a heat transfer fluid, such as oil, with the aim of heating the contents of the first tank to a predetermined temperature. 
     In accordance with a practical embodiment, the second reactor may comprise a second vessel intended to be at least partially filled with a monomer solution, a second cover which is mounted in a fluid-tight manner on the second vessel, a second drain outlet connected to the monomer solution inlet of the first reactor in order to drain the monomer solution from the second reactor into the first reactor. Advantageously, the second vessel may comprise a second double wall in a manner such as to define a peripheral circuit for circulating a heat transfer fluid, such as oil, with the aim of heating the monomer solution of the second vessel to a predetermined temperature. 
     The spirit of the invention lies in the fact that the steps for oxidation and grafting are carried out in the same reactor. The use of a second reactor which is entirely dedicated to the preparation of the monomer solution makes it possible to sequence the two steps for oxidation and grafting in time, namely firstly, oxidation by ozonation and then grafting by polymerization. Preparing the monomer solution in the second reactor also makes it possible to reduce the total treatment time, given that the monomer solution can be prepared and heated to the appropriate temperature during the oxidation step. Thus, the monomer solution is brought into the first reactor under optimal “ready for use” conditions. 
     The invention will now be described in more detail with reference to the accompanying single figure which illustrates, by way of non-limiting example, an industrial polymerization station which can be used to carry out the method of the invention. 
     The single figure is a diagrammatic view showing an industrial polymerization station of the invention. This station comprises two reactors R 1  and R 2  which may be identical or similar, but which have different uses. 
     The first reactor R 1  comprises a first vessel T 1  intended to receive the articles with a view to their oxidation and their grafting. The articles are preferably polymeric or ceramic: they may, for example, be a nonwoven textile material produced from polymer fibres such as polycaprolactone, PCL. It may also be a ceramic substrate which may comprise or be constituted by tricalcium phosphate, and more particularly b tricalcium phosphate. These are merely non-limiting examples. 
     The first tank T 1  comprises an inlet I for at least partially filling it with water or with a solution of monomer Sm in order to immerse the articles. The first tank T 1  also comprises a first drain outlet (V 1 ) for draining it of its contents, namely ozonated water or spent monomer solution, as will be described below. 
     The first tank T 1  comprises a first double wall Wi, We, in a manner such as to define a peripheral circuit Cp for the circulation of a heat transfer fluid, such as oil, with the aim of heating the contents of the first tank T 1  to a predetermined temperature. The heat transfer fluid is circulated by means of a first external pump P 1  and the temperature is raised by heating means (not shown). 
     The first tank T 1  contains a stirrer S 1  which is actuated by an external motor M 1 . The purpose of the stirrer S 1  is to mix the contents of the first tank T 1 . 
     The first reactor R 1  also comprises a first cover L 1  which is mounted in a fluid-tight manner on the first vessel T 1 . The cover L 1  is removable in order to access the inside of the first vessel T 1 , in a manner such as to be able to place the articles to be grafted therein and to recover them once the grafting has been carried out. The first cover L 1  is provided with an ozone inlet To in order to generate ozone bubbles in the first tank T 1  with the aim of oxidizing the surface of the articles immersed in the water. The ozone inlet To is in the form of a tube which passes through the first cover L 1  at a seal S 1  and extends towards the bottom of the first tank T 1 . Thus, this tube makes it possible to inject ozone into the first tank T 1  when it is filled (partially or completely) with water. The tube is connected via a pipe to an ozonator Oz, which in turn is connected to a dioxygen source So via a flowmeter Do. The first cover L 1  is also equipped with a first thermometer Th 1  and a first gas valve Vg. It should be noted that the ozone inlet To may also be connected to an inert gas source Sa (for example argon) via a flowmeter Da. The cover L 1  may also enable pipes connected to an instrument for continuous measurement of the ozone level of the tank T 1  to be introduced. 
     The second reactor R 2  comprises a second vessel T 2  which comprises an inlet Im for at least partially filling it with either water and monomer powder in order to create a solution of monomer Sm, or with a solution of monomer Sm. The second tank T 2  also comprises a second drain outlet V 2  for draining its contents, namely the ready for use monomer solution, as will be described below. 
     The second tank T 2  comprises a second double wall Wi, We, in a manner such as to define a peripheral circuit Cp for the circulation of a heat transfer fluid, such as oil, with the aim of heating the contents of the second tank T 2  to a predetermined temperature. The heat transfer fluid is circulated by means of a second external pump P 2  and the temperature is raised by heating means (not shown). 
     The second tank T 2  contains a second stirrer S 2  which is actuated via a second external motor M 2 . The purpose of the second stirrer S 2  is to dissolve the monomer powder in water in the second tank T 2  in a homogeneous manner. 
     The second reactor R 2  also comprises a second cover L 2  which is mounted in a fluid-tight manner on the second vessel T 2 . The second cover L 2  is preferably removable in order to access the interior of the second tank T 2 . The second cover L 2  is provided with an inert gas inlet Ta. The inlet Ta is in the form of a tube which passes through the second cover L 2  at a seal S 2  and advantageously extends towards the bottom of the second vessel T 2 . Thus, this tube Ta makes it possible to inject an inert gas such as argon into the second vessel T 2  when it is filled (partially or completely) with a solution of monomer Sm. The tube is connected via a pipe to the source of inert gas Sa (for example argon) via the flowmeter Da. It should be noted that the source of inert gas Sa and the flowmeter Da may be common to the two reactors R 1  and R 2 . 
     In accordance with the invention, the second discharge outlet V 2  from the second reactor R 2  is connected in series to the inlet I of the first reactor R 1  via a duct D 21  in a manner such that the contents (monomer solution Sm) of the second vessel T 2  can be poured or transferred into the first vessel T 1 . Thus, the solution of monomer Sm which is prepared and heated in the second reactor R 2  may fill the first vessel T 1 , where it may be maintained at the same temperature, left to cool or in fact heated. 
     The transfer of the solution of monomer Sm preferably takes place after having emptied the ozonated water from the first tank T 1 . In the processing order, the surface of the articles is firstly oxidized by ozonation and then coated with bioactive polymer, such as PolyNaSS, by radical grafting. As a consequence, the articles are initially immersed in water which will be ozonated by bubbling ozone through in order to carry out the surface oxidation, and then immersed in the solution of monomer Sm deriving from the second reactor R 2  in order to carry out the grafting by radical polymerization. The articles are therefore successively oxidized and grafted in one and the same reactor, namely the first reactor R 1 : the second reactor R 2  serves only to prepare the solution of monomer Sm by mixing and heating in order to be transferred into the first tank T 1  in a “ready for use” state. This therefore ensures that there will be no other substances in the reactor R 2  other than water and monomer powder. In addition, the duration of the treatment is considerably reduced, given that the oxidation step and the step for preparing the solution of monomer Sm can be carried out simultaneously and that it is the solution Sm which is transferred to come into contact with the articles, and not vice versa. 
     Furthermore, it is advisable to maintain the first reactor R 1 , and advantageously also the second reactor R 2 , at a slight overpressure by injection of an inert gas such as argon by means of the source Sa and the tubes To and Ta. 
     In addition, the water may be introduced into the first reactor R 1  by any means and preferably via the inlet I which receives the water from the second reactor R 2 . 
     The durations and temperatures of the operations of oxidation, of preparation of the solution of monomer Sm and of grafting depend on the article to be treated and on the desired degree of grafting. By way of indication, the temperature of the solution of monomer Sm in the second reactor R 2  may be of the order of 40° C. to 80° C. and the temperature of the ozonated water in the first reactor R 1  may be of the order of 20° C. to 40° C. 
     Because of the invention, articles can be oxidized and grafted industrially in one and the same reactor R 1 . Advantageously, it is possible to reduce the duration of the treatment while controlling it perfectly, by preparing the solution of monomer Sm in a second dedicated reactor R 2  mounted upstream of the first reactor R 1 .