Use of a composition including a halogenated thermoplastic polymer in a roofing element to improve a specific performance compromise

Abstract

The present invention relates to the use of at least one composition comprising at least one halogenated thermoplastic polymer in a roofing element, such as a slate, to improve the performance trade-off between density, gloss and fire resistance.

Description

Title of the invention: Use of a composition comprising a halogenated thermoplastic polymer in a roofing element to improve a specific performance compromise

[0001] The present invention relates to the use of a composition comprising at least one halogenated thermoplastic polymer in a roofing element, such as a slate, to improve a performance compromise between density, gloss and fire resistance. technical field

[0002] In the construction of structures, particularly buildings, the roof of the structure must first and foremost be capable of protecting the interior of the structure from the external environment, but also of providing a desired aesthetic appearance. The roof of the structure must therefore be made of elements exhibiting, in particular, weather-resistant properties.

[0003] Today, various materials have been used to achieve these objectives, such as slate tiles or fiber cement tiles, etc.

[0004] Slate tiles, known as "natural" slate tiles, cut from schist rock, are particularly well known. However, these slate tiles are heavy, do not have satisfactory resistance properties, and their aesthetic appearance is not necessarily pleasing.

[0005] Thus, the compositions of the prior art lead to the production of slates which have high densities.

[0006] It is therefore sought roofing elements whose use makes it possible to overcome at least the disadvantages mentioned above.

[0007] The applicant discovered that the use of at least one composition comprising at least one halogenated thermoplastic polymer in a roofing element, such as a slate, made it possible to improve a specific performance trade-off between density, gloss and fire resistance. Description of the invention

[0008] The present invention therefore relates to the use of at least one composition comprising at least one halogenated thermoplastic polymer in a roofing element, such as a slate, to improve a performance compromise between density, gloss and fire resistance.

[0009] A roofing element with a lower density than a prior art roofing element offers a benefit in terms of mass. This is a very attractive advantage at a time when lighter materials are in demand. Indeed, a Lighter materials reduce the load on the structure, thus extending the lifespan of existing buildings or allowing for lighter structures in new buildings. A reduction in mass also leads to lower overall construction costs and positive environmental impacts (helping to comply with RE2020 regulations).

[0010] Good fire resistance is obviously fundamental in a building structure.

[0011] Enhanced gloss, on the other hand, provides an aesthetic benefit. Indeed, reducing gloss allows for matte products, which thus offer both aesthetic appeal and comfort by preventing glare.

[0012] Any interval of values ​​designated by the expression "between a and b" represents the domain of values ​​going from more than a to less than b (that is to say, bounds a and b excluded) while any interval of values ​​designated by the expression "from a to b" means the domain of values ​​going from a to b (that is to say, including the strict bounds a and b).

[0013] Other features and advantages of the invention will become clearer upon reading the description and examples that follow.

[0014] The expression "at least one" is equivalent to the expression "one or more".

[0015] Furthermore, the term "pce", well known to those skilled in the art, means in the context of this patent application, part by weight per hundred parts of elastomers, in the context of the preparation of the composition before cooking.

[0016] The rubber powder itself has a composition whose ingredients can be expressed in parts per cent, the term parts per cent of elastomers, in the sense of the composition proper of the rubber powder.

[0017] On this basis, the term "pcpth" means, for the purposes of this patent application, part by weight per hundred parts by weight of halogenated thermoplastic polymers.

[0018] When referring to a "majority" compound, for the purposes of this invention, it is understood that this compound is the majority among the compounds of the same type in a given composition; that is to say, it is the one that represents the greatest quantity by mass among the compounds of the same type, and in particular more than 50% by mass, preferably more than 75% by mass. Thus, for example, a major polymer is the polymer representing the greatest mass relative to the total mass of the polymers in a given composition. Similarly, a so-called major filler is the one representing the greatest mass among the fillers in a given composition. By way of example, in a system comprising a single polymer, this polymer is the major component for the purposes of this invention; and in a system comprising two polymers, the major polymer represents more than half the mass of the polymers. Conversely, a "minority" compound is a compound that does not does not represent the largest mass fraction among compounds of the same type.

[0019] The compounds mentioned in the description may be of fossil origin or bio-based. In the latter case, they may be partially or totally derived from biomass or obtained from renewable raw materials derived from biomass. This includes, in particular, polymers, plasticizers, fillers, etc.

[0020] Furthermore, the compounds mentioned in the description may be derived from recycling. For example, a material such as powder may come from used tires or, more generally, from used materials. Another material, such as polyvinyl chloride, may come from used products, for example, those from carpentry, shutters, pipes, etc. halogenated thermoplastic polymer

[0021] The composition used according to the invention comprises at least one halogenated thermoplastic polymer.

[0022] For the purposes of this invention, thermoplastic polymer means a polymer having a glass transition temperature, or a melting temperature in the case of semi-crystalline polymers, greater than or equal to 80°C, preferably ranging from 80°C to 250°C, more preferably ranging from 80°C to 200°C, and in particular ranging from 80°C to 180°C.

[0023] Indeed, in the case of a semi-crystalline polymer, a melting temperature higher than the glass transition temperature can be observed. In this case, the melting temperature, and not the glass transition temperature, is taken into account for the definition above.

[0024] It is clear that a thermoplastic polymer within the meaning of the present invention is different from a thermoplastic elastomer.

[0025] For the purposes of this invention, halogenated thermoplastic polymer means a thermoplastic polymer as defined above, comprising units derived from one or more monomers, at least one of which comprises at least one halogen atom, such as fluorine, chlorine, bromine, iodine, preferably fluorine and chlorine, more preferably chlorine.

[0026] By average molecular mass of a halogenated thermoplastic polymer, we preferably mean the average molecular mass by weight (Mw).

[0027] Preferably, the halogenated thermoplastic polymer(s) consist of more than 75% by weight, preferably more than 85% by weight, preferably even more than 95% by weight, better than 100% by weight, of units derived from one or more monomers comprising at least one halogen atom.

[0028] Preferably, the monomer(s) comprising at least one halogen atom are chosen from vinyl tetrafluoride, vinyl fluoride, vinylidene fluoride, ethylene chlorotrifluoride, vinyl chloride, the superchlorinated vinyl chloride, vinylidene chloride, and mixtures of these monomers, and more preferably the monomer comprising at least one halogen atom is vinyl chloride.

[0029] Advantageously, the halogenated thermoplastic polymer(s) are present in a mass percentage of at least 50% by mass, preferably at least 60% by mass, more preferably 60 to 90% by mass relative to the total mass of the composition.

[0030] The composition used according to the invention may optionally include one or more thermoplastic polymers other than the halogenated thermoplastic polymers described above.

[0031] Examples of such polymers may include, in particular, acrylonitrile, butadiene and styrene copolymers (ABS copolymers), ethylene and vinyl acetate (EVA) copolymers, and mixtures thereof.

[0032] When present in the composition, non-halogenated thermoplastic polymers preferably represent a mass percentage less than or equal to 30% by mass, more preferably from 0 to 15% by mass relative to the total mass of the composition.

[0033] More preferably, the composition used according to the invention comprises as a thermoplastic polymer only one or more halogenated thermoplastic polymers according to the invention as described above.

[0034] Advantageously, said halogenated thermoplastic polymer has a weight average molecular mass (Mw) of 50,000 to 250,000 g / mol, preferably of 70,000 to 200,000 g / mol. Rubber powder

[0035] The composition used according to the invention may further comprise at least one rubber powder.

[0036] In the following, the expressions "rubber powder", "powder", "rubber powder composition" and "powder composition" are equivalent.

[0037] The powders are in the form of granules, possibly in the form of a rubber sheet. Most often, rubber powders are obtained by grinding or micronizing cooked rubber compositions already used for a first application, for example in tires; they are a recycled material product. Preferably, the powders are in the form of microparticles.

[0038] For the purposes of this invention, "microparticles" means particles whose size, namely their diameter in the case of spherical particles or their largest dimension in the case of anisometric particles, is a few tens of or hundreds of microns.

[0039] Preferably, the rubber powder is a composition comprising at least one elastomer and at least one filler.

[0040] They may also include all ingredients used in rubber compositions such as plasticizers, antioxidants, vulcanizing additives, etc.

[0041] Powders can be commercially available. According to a particular embodiment, recycled tires can be used. The powder itself, if not purchased directly from the market, can be obtained using techniques known to those skilled in the art of grinding or micronization.

[0042] The elastomer can be chosen from diene elastomers, alone or in mixture.

[0043] By filler is meant any type of filler, well known to those skilled in the art. Preferably, the filler is any type of reinforcing filler known for its ability to reinforce a rubber composition, for example an organic filler such as carbon black, an inorganic reinforcing filler such as silica or alumina possibly in the presence of a coupling agent, or mixtures thereof, for example a cutting of these two types of filler.

[0044] According to a preferred embodiment of the invention, the powder comprises, as a filler, a reinforcing filler, preferably the reinforcing filler is chosen from carbon blacks.

[0045] According to a more preferred embodiment, the reinforcing filler consists of carbon black or a mixture of carbon blacks.

[0046] As carbon blacks, all carbon blacks are suitable, in particular blacks of the type HAF, ISAF, SAF, FF, FEF, GPF and SRF conventionally used in tire rubber compositions (so-called tire grade blacks).

[0047] According to a preferred embodiment of the invention, the powder contains between 5 and 80% by mass of filler, more preferably between 10% and 75% by mass, very preferably between 15% and 70% by mass, better from 20 to 60% by mass, and better still from 20 to 50% by mass relative to the total mass of the powder.

[0048] The powder may contain all other common additives that are part of a rubber composition. These common additives include vulcanizing agents, non-reinforcing fillers such as chalk and kaolin, and preservatives. These additives may also be present in the powder in the form of residues or derivatives, since they may have reacted during the manufacturing or crosslinking stages of the composition from which the powder is derived, or they may have changed during use in the case of powder derived from end-of-life products.

[0049] The powders can be simple rubber grinds / micronized, without Other treatments. It is also known that these powders can undergo treatment to modify them. This treatment may consist of a chemical modification for functionalization or devulcanization. It may also involve thermomechanical, thermochemical, or biological treatment.

[0050] According to a first, preferred embodiment of the invention, it is possible to use a powder that has not undergone modification by thermal and / or mechanical, and / or biological and / or chemical treatment.

[0051] Preferably also according to this first embodiment, the powder has an average particle size (D50) between 50 and 800 pm, preferably between 200 and 600 pm.

[0052] According to a second embodiment of the invention, it is possible to use a powder that has a morphology modified by thermal and / or mechanical, and / or biological and / or chemical treatment.

[0053] Grinding can be carried out using various technologies, including cryogenic impact micronization technologies that produce small particles in rubber materials. Commercial equipment such as the Netzsch CUM150 or Alpine CW250 mills can be used.

[0054] Advantageously, the rubber powder is present at a mass rate of 10 to 40% by mass, preferably 10 to 35% by mass, more preferably 15 to 35% by mass relative to the total mass of the composition.

[0055] Advantageously, the roofing element has a thickness varying from 1 to 10 mm, preferably from 2 to 7 mm, more preferably from 3 to 5 mm, even more preferably from 3 to 4.5 mm. Other possible additives

[0056] The compositions used according to the invention optionally also include various additives, such as mineral or organic fillers, such as chalk, kaolin, wood powder, etc., pigments, such as carbon black, titanium dioxide, mineral pigments such as metal oxides or organic pigments, mineral or organic flame retardants, stabilizers, protective agents such as antioxidants, photoprotective agents, such as anti-UV agents, rheological additives such as plasticizers, lubricants, mineral powder, etc.

[0057] According to a preferred embodiment, the composition further comprises at least one additive, preferably selected from pigments such as carbon black, mineral powders and mixtures thereof.

[0058] Advantageously, the additive is present at a mass rate ranging from 0.2 to 20% by mass relative to the total mass of the composition. Preparation of compositions

[0059] The compositions used according to the invention are manufactured in suitable mixers commonly used for producing compositions comprising a halogenated thermoplastic polymer. The process involves two stages. The first, called "dry blending," consists of mixing the polymer powders and additives in a first heated tank (at a temperature between 80 and 120°C), then continuing the mixing and cooling in a cold tank (at ambient temperature). The resulting mixture is then fed into an extruder heated to between 130 and 200°C, producing a rod at the die exit. This rod is then cooled and granulated to produce granules of the composition.

[0060] The introduction of the possible powder can be carried out either in the "dry tank mixing" stage, with all the products in the hot tank, or introduced into the extruder's feed hopper.

[0061] When using recycled halogenated thermoplastic polymer, it can be introduced either in the "dry tank mixing" step or during extrusion.

[0062] Another embodiment consists of introducing all the components in a single extrusion step. When using halogenated polymer exclusively from recycling, the single extrusion step will be preferred, with the recycled PVC, powder, and various additives being introduced into the hopper. In this embodiment, the additives can be introduced as a masterbatch supported in a halogenated thermoplastic polymer base, such as a PVC base.

[0063] A final embodiment involves using an internal haake-type mixer or a calender heated between 130°C and 190°C. The various components are introduced into the mixer simultaneously or successively. Mixing is carried out for a period of 1 to 5 minutes.

[0064] The following examples illustrate the invention without however limiting it. Examples

[0065] In the examples, the rubber powders are characterized as indicated below.

[0066] Particle size measurement

[0067] The particle size (in particular D50) can be measured by laser particle size analysis using the Malverne Mastersizer 3000. The measurement is performed in liquid form, with dilution in alcohol after a preliminary ultrasonic treatment of 1 minute 10 seconds to ensure particle dispersion. The measurement is performed in accordance with ISO 13320-1.

[0068] Measurement of the mass fraction of carbon black and ash

[0069] The mass fraction of carbon black is measured by thermogravimetric analysis (TGA) according to standard NF T-46-07, using a Mettler Toledo model "TGA / DSC1" analyzer. Approximately 20 g of sample are introduced into the thermal analyzer and then subjected to a thermal program from 25 to 400°C under an inert atmosphere (pyrolyzable phase) and then from 400 to 750°C under an oxidizing atmosphere (oxidizable phase). The mass of the sample is measured continuously throughout the thermal program. The black content corresponds to the mass loss measured during the oxidizable phase, divided by the initial sample mass. The ash content corresponds to the residual mass at the end of the test, divided by the initial sample mass.

[0070] Fire test

[0071] The test consists of placing a sample of the product in a closed chamber at a 45° angle to the horizontal and exposing it to thermal radiation (30 kW / m²) on its lowest surface. The test lasts 20 minutes. The sample dimensions are as follows: length 40 cm, width 25 cm, thickness 4 mm. The test is carried out according to standard NF P 92-501. The ignition and extinction times of the surfaces are recorded, as well as the changes in flame heights during the test. The parameter q is calculated according to the equation of the test standard: q = (100 x Sum of flame heights (cm)) / (time of first ignition (s)) * square root (sum of effective combustion times (s)). The M classification is determined according to the value of q in accordance with standard NF P 92-507:

[0072] MO: incombustible;

[0073] Ml: non-flammable fuel q < 2.5;

[0074] M2: fuel that is difficult to ignite 2.5 < q < 15;

[0075] M3: moderately flammable fuel 15 < q < 50;

[0076] M4: highly flammable fuel q > 50;

[0077] NC: Not classified, test stopped before 20 min due to chamber fire.

[0078] Measurement of brightness

[0079] The measurement is performed using an Erichsen Picogloss 560MC glossmeter at a 60° angle. The surface of a 25 cm x 40 cm test specimen is divided into 40 squares, each 5 cm on a side. A gloss measurement is taken at the center of each square, parallel to the width and parallel to the length of the sample. A total of 80 measurements per composition are performed to obtain statistical accuracy for the gloss.

[0080] Density measurement

[0081] Density is measured using a helium pycnometer according to DIN 66137. It consists of measuring the volume occupied by a sample of a given mass in a chamber using a gas. The mass-volume (or density) is calculated from the measured volume and mass of the sample. Example 1 1. Preparation of compositions

[0082] The compositions are manufactured by introducing all the constituents into a 250 cm³ Banbury-type internal mixer. Mixing is carried out with paddle rotation speeds of 50 rpm and a tank temperature of 165°C. Mixing is stopped when the material temperature reaches 190°C. The material is then removed from the mixer and cooled, then re-entered into the mixer for another identical mixing step until the temperature reaches 190°C. A third, similar mixing step is then performed.

[0083] The Cl and C2 compositions used according to the invention were prepared based on the ingredients as described in Tables 1 and 2 below. In Table 1, the contents are expressed as % by mass. In Table 2, the contents are expressed as pcpth.

[0084]

[0085] [Tables 1] Composition (% by mass) Cl (inv) C2 (inv) Halogenated thermoplastic polymer (1) 87.7 61 Carbon black (3) 8.8 6 Stabilizer (4) 3.5 2.5 Powder (5) - 30.5

[0086] (1): Lacovyl SI 10P polyvinyl chloride (PVC) polymer marketed by the Kemone company;

[0087] (3): ASTM N234 carbon black;

[0088] (4): Naftosafe G WX 380 3-D stabilizer marketed by Chemson polymer-Additive AG;

[0089] (5): MRP Microdyne 830 TR powder dispenser marketed by Lehigh Tech nologies.

[0090] [Tables2] Composition (pcpth) Cl (inv) C2 (inv) Halogenated thermoplastic polymer (1) 100 100 Carbon black (3) 10 10 Stabilizer (4) 4 4 Powder (5) - 50 2. Sample preparation

[0091] Then, each of the compositions was shaped to obtain a plate. 3. Results

[0092] The results are summarized in Table 3 below:

[0093] [Tables3] Composition Cl (inv) C2 (inv) Density (g / cm³) 1.4 1.3 Classification M M1 M2 Gloss 4.1 3.6

[0094] It is clear that the compositions used according to the invention, C1 and C2, exhibit low density and gloss. It should also be noted that composition C2 has lower density and gloss than composition C1. The density and gloss properties are therefore even more advantageous for composition C2 than for composition C2. In particular, the gloss is even lower, i.e., even more improved. Indeed, the reduction in gloss provides an aesthetic benefit for applications aimed at obtaining matte products, such as roofing elements.

[0095] Moreover, the mass benefit associated with the use of such compositions is significant for roofing elements, i.e. an application requiring large volumes of material.

[0096] Moreover, the compositions used according to the invention Cl and C2 have a classification Ml and M2, respectively, that is to say that the compositions used according to the invention have a very advantageous and very suitable fire resistance for roofing elements.

[0097] Therefore, the use of the compositions according to the invention makes it possible to obtain an excellent compromise of performance between density, gloss and fire resistance. Example 2 1. Preparation of compositions

[0098] The compositions are manufactured in the same way as before, as described in Example 1.

[0099] The compositions C3, C4 and C5 used according to the invention were prepared on the basis of the ingredients as described in Tables 4 and 5 below.

[0100] [Tables4] Composition (% by mass) C3 (inv) C4 (inv) C5 (inv) Halogenated thermoplastic polymer (2) 97 68 65.4 Carbon black (3) 3 2 2 Stabilizer (4) - - 2.6 Powder (5) - 30 30

[0101] (2): Polyvinyl chloride (PVC) polymer Vinika VRIN713001W001 com marketed by the company MCPP.

[0102] [Tables5] Composition (pcpth) C3 (inv) C4 (inv) C5 (inv) Halogenated thermoplastic polymer (2) 100 100 100 Carbon black (3) 3 3 3 Stabilizer (4) - - 4 Powder (5) - 44 46 2. Sample preparation

[0103] Then, each of the compositions was shaped to obtain a plate. 3. Results

[0104] The results are summarized in Table 6 below:

[0105] [Tableauxô] Composition C3 (inv) C4 (inv) C5 (inv) Density (g / cm³) 1.4 1.3 1.3 Classification M M1 M2 M2 Gloss 4.1 3.6 3.6

[0106] The same observations that were made for example 1 are valid here as well.

[0107] It is clear that the compositions used according to the invention C3 to C5 exhibit low density and gloss. It should also be noted that the compositions used C4 and C5 exhibit lower density and gloss than those of composition used C3. The density and gloss properties are therefore even more advantageous for compositions used C4 and C5 than for composition C3. In particular, the gloss is even lower, i.e., even more improved.

[0108] Moreover, the mass benefit associated with the use of such compositions is significant for roofing elements, i.e. an application requiring large volumes of material.

[0109] Furthermore, the compositions used according to the invention C3, C4 and C5 have a classification M1, M2 and M2, respectively, that is to say that the compositions used according to the invention have a very advantageous and very suitable fire resistance for roofing elements.

[0110] Therefore, the use of the compositions according to the invention makes it possible to obtain an excellent compromise of performance between density, gloss and fire resistance. Example 3 1. Preparation of compositions

[0111] The compositions are manufactured in the same way as before, as described in Example 1.

[0112] Compositions C6 and C7 used according to the invention were prepared on the basis of the ingredients as described in Tables 7 and 8 below:

[0113]

[0114] [Tables7] Composition (% by mass) C6 (inv) C7 (inv) Halogenated thermoplastic polymer (6) 87.7 61 Carbon black (3) 8.8 6 Stabilizer (4) 3.5 2.5 Powder (5) - 30.5

[0115] (6): Polyvinyl chloride (PVC) polymer Evervinyl ExtriGOMOôNB com marketed by the company Paprec;

[0116] [Tables8] Composition (pcpth) C6 (inv) C7 (inv) Halogenated thermoplastic polymer (6) 100 100 Carbon black (3) 10 10 Stabilizer (4) 4 4 Powder (5) - 50 2. Sample preparation

[0117] Then, each of the compositions was shaped to obtain a plate. 3. Results

[0118] The results are summarized in Table 9 below:

[0119] [Tables9] Composition C6 (inv) C7 (inv) Density (g / cm³) 1.4 1.3 Classification M M1 M2 Gloss 4.1 3.6

[0120] The same observations that were made for examples 1 and 2 are valid here as well.

[0121] It is clear that the compositions used according to the invention, C6 and C7, exhibit low density and gloss. It should also be noted that composition C7 has lower density and gloss than composition C6. The density and gloss properties are therefore even more advantageous for composition C7 than for composition C6. In particular, the gloss is even lower, i.e., even more improved.

[0122] Moreover, the mass benefit associated with the use of such compositions is significant for roofing elements, i.e. an application requiring large volumes of material.

[0123] Furthermore, the compositions used according to the invention C6 and C7 have a classification M1 and M2, respectively, that is to say that the compositions used according to the invention have a very advantageous and very suitable fire resistance for roofing elements.

[0124] Therefore, the use of the compositions according to the invention makes it possible to obtain an excellent compromise of performance between density, gloss and fire resistance.

Claims

Demands

1. Use of at least one composition comprising at least one halogenated thermoplastic polymer in a roofing element, such as a slate, to improve the performance trade-off between density, gloss and fire resistance.

2. Use according to claim 1, characterized in that the halogenated thermoplastic polymer(s) are made up of more than 75% by mass, preferably more than 85% by mass, preferably still more than 95% by mass, better than 100% by mass, of units derived from one or more monomers comprising at least one halogen atom.

3. Use according to claim 2, characterized in that the monomer(s) comprising at least one halogen atom are selected from vinyl tetrafluoride, vinyl fluoride, vinylidene fluoride, ethylene chlorotrifluoride, vinyl chloride, superchlorinated vinyl chloride, vinylidene chloride, and mixtures of these monomers, and more preferably the monomer comprising at least one halogen atom is vinyl chloride.

4. Use according to any one of the preceding claims, characterized in that the halogenated thermoplastic polymer(s) are present in a mass percentage of at least 50% by mass, preferably at least 60% by mass, more preferably 60 to 90% by mass relative to the total mass of the composition.

5. Use according to any one of the preceding claims, characterized in that said halogenated thermoplastic polymer has a weight average molecular mass Mw of 50,000 to 250,000 g / mol, preferably of 70,000 to 200,000 g / mol.

6. Use according to any one of the preceding claims, characterized in that the composition comprises at least one rubber powder.

7. Use according to the preceding claim, characterized in that the rubber powder is a composition comprising at least one elastomer and at least one filler.

8. Use according to claim 7, characterized in that the elastomer is selected from diene elastomers, alone or in mixture.

9. Use according to claim 7 or 8, characterized in that the filler is a reinforcing filler, preferably selected from blacks of carbon.

10. Use according to any one of claims 7 to 9, characterized in that the mass percentage of charge is between 5 and 80% by mass of charge, more preferably between 10% and 75% by mass, very preferably between 15% and 70% by mass, better from 20 to 60% by mass, and better still from 20 to 50% by mass relative to the total mass of the powder.

11. Use according to any one of claims 6 to 10, characterized in that the rubber powder has an average particle size (D50) between 50 and 800 pm, preferably between 200 and 600 pm.

12. Use according to any one of claims 6 to 11, characterized in that the rubber powder is present at a mass rate of 10 to 40% by mass, preferably 10 to 35% by mass, more preferably 15 to 35% by mass relative to the total mass of the composition.