REDUCTION IN VOC AND FOG VALUES OF POLYPROPYLENE GRADES BY AERATION

Abstract

A process for reducing the amount of volatile and semi-volatile organic substances of a polypropylene composition to below 150 μg/g (VOC, VDA 278 October 2011) and below 350 μg/g (FOG, VDA 278 October 2011).

Claims

1. A process for reducing the volatile and semi-volatile organic compounds (VOC and FOG values) of a polypropylene composition to below 150 μg/g (VOC, VDA 278 October 2011) and below 350 μg/g (FOG, VDA 278 October 2011), the polypropylene composition including a polypropylene homopolymer and/or a polypropylene random copolymer, the process comprising the steps of: a) providing an aeration vessel having: at least one inlet for aeration gas, at least one outlet for exhaust gas, an inlet for a raw polypropylene composition at the top of the aeration vessel, an outlet for the polypropylene composition at the bottom of the aeration vessel; wherein the polypropylene composition is present as a packed bed; b) initiating a counter-current flow of the polypropylene composition and aeration gas; c) by feeding the raw polypropylene composition showing a VOC value of greater than about 150 μg/g and an FOG value of greater than about 350 μg/g (VOC and FOG values according to VDA 278 October 2011), into said aeration vessel from the top; feeding the aeration gas into said aeration vessel via the at least one inlet at the bottom; withdrawing the exhaust gas via the outlet for exhaust gas; withdrawing the aerated polypropylene composition via the outlet at the bottom of the aeration vessel; d) maintaining said aeration gas flow for an aeration time of from 3 to 96 hours, wherein, the temperature of the aeration gas is from 100° C. to 150° C., and wherein the Reynolds number (Re) of the gas flow is from 5 to 150, whereby the Reynolds number for the flow of aeration gas through the packed bed is defined by formula (I):
Re=(ρ.Math.v.sub.s.Math.D)/μ  (I) where: ρ is the density of the aeration gas at the temperature used (kg/m.sup.3), μ is the kinematic viscosity of the aeration gas at the temperature used (kg/ms), v.sub.s is the superficial velocity, defined as Q/A where Q is the volume flow rate of the aeration gas, (m.sup.3/s) and A is the cross sectional area (m.sup.2), and D is the diameter (m) of the particles.

2. The process according to claim 1, wherein the Reynolds number of the gas flow is from 5 to 150.

3. The process according to claim 1, wherein the aeration gas is air.

4. The process according to claim 1, wherein the process is continuous.

5. The process according claim 1, wherein the raw polypropylene composition is in pellet form and the pellets have a diameter D in the range of 2.5 mm up to 5 mm.

6. The process according to claims 5, wherein the pellets are pre-heated before being added to the aeration vessel.

7. The process according to claim 1, wherein at least one component of the raw polypropylene composition originates from a solution polymerisation process.

8. The process according to claim 1, wherein the polypropylene composition after aeration has a ratio of FOG/VOC of more than 5.0.

9. The process according to claim 1, wherein the aeration process is operated for less than 24 hours.

10. The process according to claim 1, wherein the temperature of the aeration gas is from about 100° C. to about 140° C.

11. The process according to claim 1, whereby the exhaust gas is subjected to a purification step and then recycled back into the inlet for the aeration gas.

12. The process according to claim 1, wherein the exhaust gas passes a heat exchanger before being discharged into the atmosphere.

13. The process according to claim 1, wherein the aeration vessel is cylindrical, or conical, or cylindrical with a cone shaped bottom portion.

14. The process according to claim 1, wherein the polypropylene composition contains at least one slip agent.

15. A product obtainable by the process according to claim 1.

Description

DETAILED DESCRIPTION

[0104] It has surprisingly been found that the reduction in both VOCs and FOGs obtained by the inventive process are excellent for the given energy, effort and aeration time. In addition, there is no need for additional circulation of the granular composition.

[0105] Furthermore, the inventive process can be used at a commercial scale to reduce VOCs and FOGs to acceptable levels with relatively low effort. Consumers generally do not want polypropylene components in cars to emit fumes caused by VOCs or to cause fogging on the windscreen through the release of semi-volatile organic components (FOG).

[0106] In a first preferred embodiment of the present invention, the aeration time is from 3 to 96 hours, preferably from 3 to 5 hours and the temperature is from 115° C. to 135° C. This embodiment aims at reducing costs.

[0107] Insofar, the first preferred embodiment of the invention relates to a process for reducing the volatile organic compound (VOC) and semi-volatile organic condensable (FOG) content of a polypropylene composition to below 150 μg/g (VOC, VDA 278 October 2011) and below 350 μg/g (FOG, VDA 278 October 2011), the polypropylene composition including a polypropylene homopolymer and/or a polypropylene random copolymer, [0108] the process comprising the steps of [0109] a) providing an aeration vessel having [0110] at least one inlet for aeration gas, [0111] at least one outlet for exhaust gas, [0112] an inlet for a raw polypropylene composition at the top of the aeration vessel, [0113] an outlet for the polypropylene composition at the bottom of the aeration vessel, [0114] wherein the polypropylene composition is present as a packed bed; [0115] b) initiating a counter-current flow of polypropylene composition and aeration gas; [0116] c) by [0117] feeding the raw polypropylene composition having a volatile organic compound content (VOC, VDA 278 October 2011) of greater than about 150 μg/g and a semi-volatile organic condensable content of greater than about 350 μg/g (FOG, VDA 278 October 2011), into said aeration vessel from the top, [0118] feeding the aeration gas into said aeration vessel via the at least one inlet at the bottom; [0119] withdrawing the exhaust gas via the outlet for exhaust gas; [0120] withdrawing the aerated polypropylene composition via the outlet at the bottom of the aeration vessel; [0121] d) maintaining said aeration gas flow for an aeration time of from 3 to 96 hours, [0122] wherein, the temperature of the gas is from 115° C. to 135° C., and wherein, the Reynolds number of the gas flow is from 5 to 150.

[0123] In a second preferred embodiment, aeration is carried out at 138° C. to 146° C., for 6 to 9 hours, with a Reynolds number of the gas flow from 15 to 50. This embodiment aims to reduce the VOC content to 100 μg/g or less, preferably 60 μg/g or less, more preferably 40 μg/g or less, and most preferably 20 μg/g or less (VOC according to VDA 278 October 2011). Additionally, this embodiment aims to reduce the amount of FOG content to 300 μg/g or less, preferably 280 μg/g or less, more preferably 250 μg/g or less (FOG according to VDA 278 October 2011).

[0124] In a third particularly preferred embodiment, aeration is carried out at 115° C. to 125° C., for 3 to 5 hours, with a Reynolds number of the gas flow from 15 to 50.

[0125] The following ranges are applicable for all embodiments according to the invention.

Aeration Gas Flow

[0126] In the process according to the present invention, the pellets are preferably subject to a warm gas-stream.

[0127] The present invention preferably provides a process, wherein the Reynolds number of the gas flow is at least about 5, preferably at least about 10, most preferably at least about 15. It is believed, that a relatively fast flow of aeration gas is desirable to achieve the objectives of the current invention, and allows for a more even reduction of volatiles (VOC, VDA 278 October 2011) and semi-volatiles (FOG, VDA 278 October 2011) throughout the entire width of the pellets. Without wishing to be bound by any theory, it is believed that a minimum Reynolds number of 5 is required to bring enough heat into the aeration vessel in order to allow the aeration process to be successful.

[0128] The present invention preferably provides a process, wherein the total normalised volumetric airflow used is from 1 to 5 Nm.sup.3/kg such as at least about 1.5 Nm.sup.3/kg preferably at least about 2 Nm.sup.3/kg such as around 2.6 Nm.sup.3/kg.

[0129] According to the present invention, the gas input is at the bottom of the aeration vessel, resulting in a gas flow from the bottom to top through the bed of the polypropylene composition. In the present invention, the gas inlet may preferably be selected from the group of: a nozzle, a series of nozzles, a gas distribution ring and a gas distribution plate.

[0130] The process according to the present invention comprises a step of optionally subjecting the gas downstream of the aeration vessel to a means for removing the hydrocarbons. Preferably, these means are selected from one or more catalytic oxidation units, one or more carbon absorption columns (drums) and/or any conventional exhaust treatment known in the art. Even more preferably, these means are carbon absorption columns (drums). Preferably, when the aeration gas is air and/or nitrogen, it can be emitted into the atmosphere after removal of hydrocarbons. Additionally, the aeration gas can be treated and re-circulated back into the aeration vessel.

[0131] Moreover, the heat still contained in the discharged gas can be transferred to the gas used for aeration via heat exchangers known in the art, if the gas taken from the environment has a temperature lower than the temperature needed for the process.

[0132] In the process according to present invention, the exhaust gas is preferably discharged into the atmosphere. Alternatively, but less preferably the exhaust gas is used again after separation of the volatile and semi-volatile substances.

Aeration Process

[0133] The present invention preferably provides an aeration process, which is operated for less than about 24 hours, or less than about 12 hours, or less than about 10 hours, such as from 3 to 9 hours. Generally, the aeration time is inversely proportional to the gas temperature meaning that a compromise must be reached to avoid the pellets melting and sticking together. Typical values for the temperature and residence time for polypropylene according to EP2005/056962 are from 80 to 110° C. for a period of from 10 to 50 hours. It is believed that the reduction in VOC values reaches a plateau following extended aeration times of greater than five hours in the conditions described here; in contrast, for FOG values there is a weaker dependence on aeration time in the period from 0 to 5 hours. It is believed that this is due to slow diffusion of higher molecular weight alkanes (C.sub.14-C.sub.32), which contribute greatly to FOG values, in contrast to the rapid diffusion of ≤C.sub.25 which are considered for VOC values.

[0134] In the process according to the present invention, the polypropylene composition is preferably not mixed or moved throughout the treatment by mechanical means. Consequently, during the aeration process the polypropylene composition is effectively stationary (apart from its vertical transit through the aeration vessel). Therefore, the present invention preferably excludes processes where the polymer composition is agitated during aeration; these processes do not fall under the scope of this invention, such as fluidised bed processes. Absence of mechanical mixing and similar measures such as re-filling or the like is particularly advantageous since the creation of fines is avoided. In addition, the filling degree is higher without the need for mechanical stirring or the need to transfer the polypropylene composition into another treatment vessel/silo.

[0135] The present invention optionally provides a process, wherein the pellets are pre-heated before being added to the aeration vessel, such as being pre-heated to at least 40° C., more preferably pre-heated to temperatures of from 80° C. to 100° C. before being added to the aeration vessel.

[0136] As the specific heat capacity of the polypropylene composition together with the mass of the polypropylene composition is significant compared to the specific heat capacity of the gas together with the mass of the gas, one has to be attentive that the gas stream temperatures are met for the inlet and the outlet of the aeration. Thus, if the polypropylene composition is provided at relatively low temperatures in a silo, a pre-heating step will be necessary. The pre-heating can also naturally be effected by the gas-stream and the temperatures as specified above. However, during such pre-heating the temperature at the outlet will be lower as the heat is transferred to the polypropylene composition.

[0137] The polypropylene composition is optionally pre-heated before the start of the aeration time to speed up the process. Generally, any heating measures known in the prior art can be used for pre-heating. The polypropylene composition may be pre-heated to temperatures of 40° C. or more, preferably 50° C. or more.

[0138] Pre-heating could also be considered as not letting the pellets cool down, which are produced, extruded and pelletized shortly beforehand. Such pellets normally have a temperature of about 40° C. or higher, preferably 50° C. or higher. Hence, the production process of the polypropylene composition and the process of the current invention can be carried out as an integrated process.

[0139] In contrast, the present invention may provide a process in which the polypropylene composition is not pre-heated before being added to the aeration vessel and in which the polypropylene is simply warmed by the flow of heated aeration gas in the silo. Without wishing to be bound by any theory, it is believed that with a relatively small pellet size (diameter of ca. 3.5 mm), the composition reaches the desired aeration temperature relatively rapidly after being added to the aeration vessel.

[0140] The aeration vessel used in the process of the present invention is not particularly limited and in principle, any commercially available aeration vessel or aeration silo may be used; in addition, customised aeration vessels, which have been specifically constructed for the purpose of aeration, may be used.

[0141] For shortening the pre-heating phase, avoiding energy loss during aeration and/or also increased homogeneity over the cross-section, the use of an isolated treatment vessel, preferentially an isolated silo is preferred. The silo may for example be a steel silo. Furthermore, the silo may be cylindrically or conically shaped.

Raw Polypropylene Composition

[0142] The present invention may provide a process, wherein the raw polypropylene composition comprises at least one filler selected from the group of natural or synthetic non-thermoplastic fillers or reinforcement, and/or at least one additive selected from the group of antioxidants, pigments, nucleating agents, and specific additives for enhancing UV stability and/or scratch resistance. Additives known to improve the scratch resistance of polypropylene compounds include erucamide, stearate and glycerol monostearate among others.

[0143] Polyolefins obtained from solution polymerization usually contain relatively high amounts of volatile and semi-volatile substances. The VOC value is, therefore, usually too high for end-use applications and the FOG value is also undesirably high (VOC and FOG according to VDA 278 October 2011). It is self-explanatory, that polypropylene compositions having other process histories may also be treated. However, usually such raw plastomers do not show undesirably high values of VOC or FOG. Polymerisation processes by their nature result in relatively high amounts of low molecular by-products. Consequently, the inventive process does not require the use of highly pure reactants and in fact, it is possible to add value to relatively impure raw polypropylene compositions.

[0144] Preferably, the raw polypropylene composition used in process of the present invention shows a VOC value of 150 μg/g or more, or 180 μg/g or more, or 200 μg/g or more. Additionally, the raw polypropylene composition used in process of the present invention may show an FOG value of 350 μg/g or more, or 400 μg/g or more (VOC and FOG according to VDA 278 October 2011).

[0145] The raw polypropylene composition used in process of the present invention may have a ratio of FOG/VOC of 5 or less, preferably 3 or less, such as between about 3 and about 2.

[0146] Preferably, the raw polypropylene composition used in process of the present invention has a total carbon emission value (TVOC) of greater than 20 μgC/g, preferably greater than 30 μgC/g, more preferably greater than 40 μgC/g (according to VDA 277 January 1995). Additionally, the raw polypropylene composition may have a fogging gravimetric, measured according to DIN 75201:2011-11, of greater than 1.2.

[0147] The raw polypropylene polymer used in the process of the present invention may comprise a crystalline polypropylene homopolymer or random copolymer component. The crystalline polypropylene homopolymer or random copolymer component may have a melting point (T.sub.m) of greater than 150° C., preferably greater than 160° C. Following aeration there is negligible change in the melting point (T.sub.m) of the polypropylene composition, such as e.g. a less than 10% reduction in melting point (T.sub.m) value, or a less than 5% reduction in melting point value, or a less than 2.5% reduction in melting point value. The melting point (T.sub.m) of the composition following aeration is, therefore, usually greater than 150° C., preferably greater than 160° C.

[0148] The crystalline polypropylene homopolymer or random polypropylene copolymer component may have an MFR.sub.2 (230° C.) of 4 to 160 g/10 min, preferably 5 to 100 g/10 min and the xylene soluble fraction an MFR.sub.2 (230° C.) from 10 to 40 g/10 min prior to aeration. The polypropylene composition prior to aeration optionally has a melting point (T.sub.m) of from 140° C. to 170° C. Following aeration the polypropylene composition optionally has a melting point (T.sub.m) of from 150° C. to 169° C. Without wishing to be bound by any theory, it is believed that the aeration process according to the present invention does not lead to a substantial change in the properties of the polypropylene compositions, such as e.g. T.sub.m.

Properties of the Polypropylene Composition Post Aeration

[0149] The polypropylene compositions which result from the inventive process show FOG values of 350 μg/g or less, preferably 300 μg/g or less, more preferably 250 μg/g or less, more preferably 200 μg/g or less, most preferably 170 μg/g or less. In addition, the polypropylene compositions that result from the inventive process may show VOC values of 150 μg/g or less, or of 80 μg/g or less, or of 60 μg/g or less, preferably of 40 μg/g or less, most preferably of 20 μg/g or less. (Both VOC and FOG values according to VDA 278 October 2011)

[0150] Preferably, the inventive process leads to polypropylene compositions with a ratio of FOG/VOC of 3 or more, preferably 5 or more, more preferably 10 or more, more preferably 13 or more (both, VOC and FOG values according to VDA 278 October 2011).

[0151] The process according to the present invention may lead to polypropylene compositions with a total carbon emission value of up to 10 μgC/g, such as less than 10 μgC/g, preferably less than 5 μgC/g, more preferably less than 2 μgC/g, most preferably less than 1 μgC/g (total carbon emission, TVOC according VDA 277 January 1995). In addition, the process may lead to polypropylene compositions with a fogging gravimetric of less than 1.2, preferably less than 1.1, most preferably less than 1.

[0152] In certain embodiments, the inventive process leads to a reduction in VOC values (VDA 278 October 2011) of the polypropylene composition of greater than 70%, preferably greater than 80%, more preferably of greater than 90%.

[0153] In certain embodiments, the inventive process leads to a reduction in FOG values (VDA 278 October 2011) of the polypropylene composition of greater than 20%, preferably greater than 30%, more preferably greater than 40%, most preferably greater than 60%. In certain embodiments, the inventive process leads to a reduction in total carbon emissions, TVOC (VDA 277, January 1995) values of the polypropylene composition of greater than 70%, preferably greater than 80%, more preferably of greater than 90%.

[0154] In certain embodiments, the inventive process leads to a reduction in Fogging gravimetric values of the polypropylene composition of greater than 5%, or greater than 10%, or greater than 50%.

[0155] In certain such embodiments, the inventive process leads to a reduction in VOC values (VDA 278 October 2011) of the polypropylene composition of greater than 70%, and a reduction in FOG values (VDA 278 October 2011) of greater than 20%, and a reduction in VDA 277 (January 1995) values of greater than 70%.

[0156] The present invention, furthermore, relates to a process for the reduction in VDA 277 (January 1995) values of polypropylene compositions and to a process for the reduction of fogging gravimetric of polypropylene compositions. The present invention preferably provides a process, wherein the polypropylene composition after aeration has a VOC of below 80 μg/g (VOC, VDA 278 October 2011) and an FOG value of below 350 μg/g (FOG, VDA 278 October 2011) and has a ratio of FOG/VOC of more than 5.0.

[0157] The puncture energy (ISO 6603-2) of the composition according to the present invention following aeration is within 10% of the puncture energy of the raw composition, preferably within 5%, more preferably within 2.5%. This demonstrates that the polypropylene composition does not lose the ability to withstand a point impact following aeration and as such can be seen as confirmation that the present invention does not lead to a reduction in the mechanical properties of the polypropylene material.

[0158] Surprisingly, the process according to the present invention does not lead to depletion of “slip agents” such as e.g. erucamide. During polypropylene production, slip agents are often added to the polypropylene blend in order to reduce the coefficient of friction of these polypropylene materials. The most popular slip agents used by industry are from the chemical group of fatty amides, such as e.g. erucamide. When a slip agent is mixed with a polypropylene polymer melt, it is absorbed into the amorphous regions of the polypropylene polymer.

[0159] On cooling the slip agent becomes incompatible with the polypropylene material because of the different surface energies of the two materials and migrates to the material surface. The rate of migration depends on the difference between the surface energies of the polypropylene and the slip agent (the larger the difference, the faster the migration). This initially leads to the formation of a monolayer on the polymer surface, followed by the deposition of subsequent layers when new molecules of the slip agent arrive on the surface leading to the formation of a double layer. Because of weak bonding between the layers of fatty amides, materials produced from polypropylene containing fatty amides will slide over each other with ease. The presence of a layer of slip agent also reduces the friction at the surface of the polypropylene composition. This property is also important, for example, when producing injection-moulded articles, as slip agents can be used to help aid the release of injection-moulded articles from a mould. Fatty amides come to the surface of polypropylene articles, when the polypropylene cools; therefore, reducing the coefficient of friction between the polypropylene article and the mould. This means that with relatively little force the polypropylene article can be removed from the mould and that no polypropylene sticks to the mould on release of the moulded article. Many slip agents in particular fatty amides, such as e.g. erucamide are relatively volatile and, therefore, care is required to prevent these materials escaping during processing steps in polymer production. The process according to the current invention does not lead to depletion of slip agents in particular fatty amides, such as e.g. erucamide. Therefore, the process according to the present invention allows the advantageous removal of volatile and semi-volatile substances, without stripping out slip agents from the polypropylene composition. Thus, in the process according to the present invention, the polypropylene composition preferably contains at least one slip agent, more preferably at least one slip agent selected from the group of fatty amides, most preferably erucamide.

Process

[0160] As mentioned above, the present invention is concerned with a process for producing polypropylene compositions showing: [0161] an FOG value of below 350 μg/g and [0162] a VOC value of below 150 μg/g;
the process comprising the steps of [0163] a) polymerizing propylene and optionally other C.sub.4-C.sub.12 alpha olefins by solution polymerisation in at least one polymerization reaction to yield a raw polypropylene polymer; [0164] b) recovering said raw polymer from the at least one polymerisation reactor and feeding said raw polymer mixture to at least one flash vessel thereby at least partially removing solvent, unreacted monomer and unreacted co-monomer to yield a raw polymer; [0165] c) mixing the polymer with a range of other components, optionally including HDPE, fillers, carbon nanoparticles among others and subjecting the raw composition to mixing, preferably by an extruder or a static mixer; [0166] d) recovering the raw polypropylene composition showing [0167] a VOC value of above 150 μg/g and [0168] a FOG value of above 350 μg/g [0169] e) subjecting said raw polypropylene composition in an aeration vessel to a gas stream with a Reynolds number (Re) of from 5 to 150 for an aeration time from 3 to 96 hours, wherein the gas has a temperature of from about 100° C. to about 150° C., [0170] f) recovering the polypropylene composition.

Product

[0171] An aspect of the present invention also relates to products obtainable by the processes described above and to articles produced therewith. Polypropylene is a versatile material that is easily processable and which finds a number of applications in the automobile industry e.g. for injection moulded components such as, e.g., dashboards or car door interior articles. Polypropylene compositions are also used as the covering for blister packaging.

[0172] All preferred ranges and embodiments as described above also hold for this integrated process and are incorporated by reference herewith.

Experimental Part

[0173] The following examples are included to demonstrate certain aspects and embodiments of the invention as described in the claims. It should be appreciated by those of skill in the art, however, that the following description is illustrative only and should not be taken in any way as a restriction of the invention.

Test Methods

Sample Preparation

[0174] VOC values, FOG values and TVOC (total carbon emission) values were measured as described below, after sample preparation consisting of injection moulding plaques in the according to EN ISO 19069-2:2016. These plaques were packed in aluminium-composite foils immediately after production and the foils were sealed.

[0175] For the thermodesorption analysis according to VDA 278 (October 2011) the samples were stored uncovered at room temperature (23° C. max.) for 7 days directly before the commencement of the analysis.

[0176] Regarding the VDA 277 (January 1995) measurements, no additional uncovered storage or other conditioning took place. Instead, the injection-moulded plaques were cut and ground in a Retsch SM-2000 mill.

[0177] In both cases (VDA 277 and VDA 278), the production date of the injection moulded plaques, the time when the sample arrived in the lab as well as the analysis date were recorded.

VOC and FOC acc. VDA278

[0178] VOC value is determined according to VDA 278 October 2011 from injection moulded plaques. VDA 278 October 2011, Thermal Desorption Analysis of Organic Emissions for the Characterization of Non-Metallic Materials for Automobiles, VDA Verband der Automobilindustrie. According to the VDA 278 October 2011 the VOC value is defined as “the total of the readily volatile to medium volatile substances. It is calculated as toluene equivalent. The method described in this Recommendation allows substances in the boiling/elution range up to n-pentacosane (C.sub.25) to be determined and analyzed.”

[0179] FOG value is determined according to VDA 278 October 2011 from injection moulded plaques. According to the VDA 278 October 2011 the FOG value is defined as “the total of substances with low volatility, which elute from the retention time of n-tetradecane (inclusive)”. It is calculated as hexadecane equivalent. Substances in the boiling range of n-alkanes “C.sub.14” to “C.sub.32” are determined and analysed.

Total Carbon Emission, TVOC:

[0180] The total carbon emission of the polypropylene composition was determined by VDA 277 (January 1995) from pellets, where VDA 277 is referred to in the application the total carbon emission is what is meant.

Fogging:

[0181] Fogging was measured according to DIN 75201:2011-11, method B (gravimetric method) on compression-moulded specimens (diameter 80 mm+/−1 mm, thickness <1 cm) cut out from an injection-moulded plate. With this method, the mass of fogging condensate on aluminium foil in mg is determined by means of weighing of the foil before and after the fogging test. The term “fogging” refers to a fraction of volatile substances condensed on glass parts as e.g. the windscreen of a vehicle.

Melt Flow Rate (MFR.SUB.2.):

[0182] The melt flow rates were measured with a load of 2.16 kg (MFR.sub.2) at 230° C. The melt flow rate is the quantity of polymer in grams, which the test apparatus standardized to ISO 1133 extrudes within 10 minutes at a temperature of 230° C. under a load of 2.16 kg.

Xylene Cold Soluble Fraction (XCS wt %):

[0183] The xylene cold soluble fraction (XCS) is determined at 23° C. according to ISO 6427.

Polymer-Puncture Plaque—Instrumented:

[0184] Puncture energy is determined in the instrumented falling weight test according to ISO 6603-2 using injection moulded plaques of 60×60×1 mm and a test speed of 2.2 m/s, clamped, lubricated striker with 20 mm diameter. The reported puncture energy results from an integral of the failure energy curve measured at (60×60×1 mm).

Diameter D

[0185] A sieve analysis according to ISO 3310 was performed. The sieve analysis involved a nested column of sieves with wire mesh screen with the following sizes: >20 μm, >32 μm, >63 μm, >100 μm, >125 μm, >160 μm, >200 μm, >250 μm, >315 μm, >400 μm, >500 μm, >710 μm, >1 mm, >1.4 mm, >2 mm, >2.8 mm, >4 mm. The samples were poured into the top sieve, which has the largest screen openings. Each lower sieve in the column has smaller openings than the one above (see sizes indicated above). At the base is the receiver. The column was placed in a mechanical shaker. The shaker shook the column. After the shaking was completed the material on each sieve was weighed. The weight of the sample of each sieve was then divided by the total weight to give a percentage retained on each sieve. The particle size distribution and the characteristic median particle size d50 was determined from the results of the sieve analysis according to ISO 9276-2.

EXPERIMENTS

[0186]

TABLE-US-00001 TABLE 1 Properties of the base resins used in the compositions used in Example 1. C2 Xylene (ethylene MFR.sub.2 solubles content) Base resin Type (g/10 min) (wt-%) (wt-%).sup.2 Resin 1 Heterophasic 100 13 6.5 polypropylene copolymer Resin 2 RTPO.sup.1 5.5 25 6.5 Resin 3 RTPO.sup.1 18 31 20 Resin 4 Heterophasic 20 18 8 polypropylene copolymer .sup.1Reactor-made polyolefin .sup.2Determined by .sup.13C-NMR spectroscopy

TABLE-US-00002 TABLE 2 The composition of each of the polypropylene compositions (A, B and C) used in Example 1 A B C Base Resin 1 46.0 29.5 resin Resin 2 21.0 15.0 10.0 Resin 3 19.5 40.5 Resin 4 25.0 HDPE 6.0 8.0 8.0 Elastomer.sup.1 7.0 4.0 Filler Talc filler 10.0 17.0 7.0 Carbon black/other carbon 7.5 4.5 6.0 Total 97.5 97.5 96.0 Propeperties.sup.2 Tm (° C.) 165 166 166 MFR (g/10 min) 20 17 13 Puncture energy 23° C., 42 39 39 4.4 m/s, 3 mm (J) Flexural modulus (MPa) 1700 1800 1400 Values are given in weight percent and rounded to the nearest 0.5 %. .sup.1An ethylene-propylene elastomer. .sup.2Properties of the raw polypropylene compositions before aeration.

Example 1 (Ex1)

[0187] Batches of pelletized polypropylene compositions, corresponding to the materials A, B and C as defined in Table 2 respectively, were subjected to aeration. Aeration was carried out in an insulated cylindrically shaped silo with dimensions of 1.5 m.sup.3. The pellets had a median particle size d50 of 3.5 mm (ISO 3310, evaluation according to ISO 9276-2).

[0188] The pellets were at room temperature (ca. 25° C.) before being subject to aeration i.e. a pre-heating step was not applied.

[0189] The aeration process was carried out for 7.5 hours at a temperature of 140° C. A gas flow rate of 260 m.sup.3/h was used. The pellets were not mixed or agitated during the process and instead simply moved vertically through the silo at a speed of 100 kg/h. This corresponds to a normalised gas flow of 2.6 Nm.sup.3/kg.

[00006]$\mathrm{Normalised}\mathrm{gas}\mathrm{flow}=\frac{\mathrm{Gas}\mathrm{flow}\mathrm{rate}}{\mathrm{Pellet}\mathrm{speed}}=\frac{260}{100}=2.6.$

[0190] The process was carried out on a 1000 kg scale. In a cylindrical silo of 1.5 m.sup.3. A relative flow rate of polypropylene composition pellets of 100 kg/h was maintained throughout the aeration process.

[0191] The aeration process was carried out continuously for about 7.5 hours.

[0192] The VOC, FOG, VDA 277 and Fogging gravimetric obtained for each grade before and after the aeration step is given in Table 4.

TABLE-US-00003 TABLE 3 Summary of the airflow characteristics used in the present experiments Value in the current experiments Units (with air) density of the fluid Kg/m.sup.3 0.85 (gas)/ kinematic viscosity of kg/m .Math. s 2.35 × 10.sup.−5 the fluid (gas)/μ* superficial velocity/ m/s 0.16 vs Diameter of the m 0.0035 particles/D (determined using method as described above) *Density and kinematic viscosity of the fluid gas (in the example: air of the given temperature) can simply be looked up for any temperature of interest in textbook tables.

[0193] Superficial velocity is calculated by dividing the volumetric airflow (i.e. m.sup.3/h) by the cross sectional area of the apparatus (m.sup.2); for the volumetric airflow, the actual flow must be used in m.sup.3/h.

[0194] The Reynolds number can be calculated using the formula:

Re=(ρ.Math.v.sub.s.Math.D)/μ

where: [0195] ρ: density of the aeration gas at the temperature used (kg/m.sup.3) [0196] μ: kinematic viscosity of the aeration gas at the temperature used (kg/ms) [0197] v.sub.s: superficial velocity, defined as Q/A where Q is the volume flow rate of the aeration gas, (m.sup.3/s) and A is the cross sectional area (m.sup.2) [0198] D: d50 diameter (m) of the particles (using sieve analysis according to ISO3310 and evaluation according to ISO9276-2)

Re=(ρ.Math.v.sub.s.Math.D)/μ

[0199] The Reynolds number for the gas flow used in the process of example 1 was 20.

TABLE-US-00004 TABLE 4 Summary of VOC, FOG, VDA 277 and Fogging gravimetric for polymers A, B and C before and after aeration. V0A278, V0A278, V0A277, Fogging Polymer VOC* FOG* TVOC** gravimetric FOG/ Units μg/g μg/g μgC/g wt.-% VOC A Before 232 460 45 1.28  2 aeration After  12 161  1 0.52 13 aeration B Before 188 400 41 1.26  2 aeration After  16 235 <1 1.08 15 aeration C Before 245 464 45 0.85  2 aeration After  14 150 <1 0.32 11 aeration Test conditions: 140° C. 7.5 h, Pellet flow: 100 kg/h, vol. airflow: 260 m.sup.3/h. VOC and FOG values were measured after 7 days of uncovered storage according to VDA 278, VDA 277 and fogging gravimetric were measured immediately **total carbon emissions

TABLE-US-00005 TABLE 5 Properties of polypropylene compositions A, B and C following aeration Percentage change Puncture in puncture energy Melting energy 23° C., before and after point, Tm 4.4 m/s, aeration Polymer (° C.) 3 mm (J) (%) A 165 42 0 B 166 40 2.5 C 166 39 0