METHOD FOR IMPREGNATING POLYMER GRANULATES

Abstract

The invention relates to a method for impregnating a polymer granulate with a predefined mass of a gaseous propellant. According to the invention, the polymer granulate is arranged inside a pressure vessel and a gaseous propellant is introduced into the inside of the pressure vessel.

Claims

1. A method for impregnating a polymer granulate (110) with a predefined mass of a gaseous propellant, wherein the polymer granulate (110) is arranged in an inside of a pressure vessel (100), a gaseous propellant is initially introduced into the inside of the pressure vessel (100), propellant being absorbed by the polymer granulate (110), and a current pressure (p.sub.2) prevailing in the inside being measured, wherein a current mass (Δm) of the propellant absorbed by the polymer granulate is determined as the difference between the mass (m.sub.1) of the total propellant initially introduced into the inside of the pressure vessel and the mass (m.sub.2) of a non-absorbed part of the propellant currently located in the inside, and wherein the method is discontinued when the current mass (Δm) of the absorbed propellant is greater than or equal to the predefined mass.

2. The method according to claim 1, wherein a current temperature (T.sub.2) in the inside of the pressure vessel (100) is measured.

3. The method according to claim 1, wherein the current mass (Δm) is determined by means of a programmable logic controller.

4. The method according to claim 1, wherein the mass of the non-absorbed part of the propellant (m.sub.2) currently located in the inside is determined by means of the relationship: $m_2=\frac{p_2.Math.V}{R_S.Math.T_2}$ wherein p.sub.2 and T.sub.2 are the current pressure and the current temperature in the inside of the pressure vessel, R.sub.S is the specific gas constant of the gas or gas mixture present in the pressure vessel, and V is the vessel volume not occupied by the polymer granulate.

5. A method for impregnating a polymer granulate with a predefined mass of a gaseous propellant, wherein the polymer granulate (110) is arranged in an inside of a pressure vessel (100), a gaseous propellant is initially introduced into the inside of the pressure vessel (100) so that propellant is absorbed by the polymer granulate (110), and wherein propellant is subsequently added to the inside of the pressure vessel (100), wherein the masses of the initially (m.sub.1) and subsequently introduced propellant (Δm.sub.a) are determined, a current mass (Δm) of the propellant absorbed by the polymer granulate is determined using the masses of the propellant initially (m.sub.1) and subsequently (Δm.sub.a) introduced into the inner space, and wherein the method is discontinued when the current mass (Δm) of the absorbed propellant is greater than or equal to the predefined mass.

6. The method according to claim 5, wherein a current temperature (T.sub.2) is measured in the inside of the pressure vessel (100).

7. The method according to claim 5, wherein the current pressure (p.sub.2) prevailing in the inside of the pressure vessel (100) is measured and the respectively subsequently introduced propellant is introduced into the inside of the pressure vessel (100) continuously, so that the pressure prevailing in the inside of the pressure vessel (100) remains constant.

8. The method according to claim 5, wherein the current mass (Δm) of the propellant absorbed by the polymer granulate (110) is determined by means of the relationship $\Delta m_b=\Delta m_a-\frac{p_1.Math.V}{R_S}.Math.\left(\frac{1}{T_2}-\frac{1}{T_1}\right)$ wherein m.sub.1 and Δm.sub.a are the masses of the propellant initially and subsequently introduced into the inside of the pressure vessel (100), wherein T.sub.1 is an initial temperature prevailing in the inside of the pressure vessel (100) before the absorption of the propellant, and wherein T.sub.2 is the current temperature in the inside of the pressure vessel, V is the volume of the pressure vessel not occupied by the polymer granulate, R.sub.S is the specific gas constant of the gas in the vessel, and p.sub.1 is the constant pressure in the pressure vessel.

9. The method according to claim 5, wherein the current pressure (p.sub.2) prevailing in the inside of the pressure vessel (100) is measured, and wherein the current mass (Δm) of the propellant absorbed by the polymer granulate is determined using the masses of the propellant initially (m.sub.1) and subsequently (Δm.sub.a) introduced into the inside and the current pressure (p.sub.2), and wherein the method is discontinued when the current mass (Δm) of the absorbed propellant is greater than or equal to the predefined mass.

10. The method according to claim 9, wherein the current mass (Δm) of the propellant absorbed by the polymer granulate (110) is determined by means of the relationship $\Delta m_b=\Delta m_a-\frac{V}{R_S}.Math.\left(\frac{p_2}{T_2}-\frac{p_1}{T_1}\right)$ wherein m.sub.1 and Δm.sub.a are the masses of the propellant initially and subsequently introduced into the inside of the pressure vessel (100), p.sub.1 and T.sub.1 are an initial pressure prevailing in the inside before absorption of the propellant and an initial temperature prevailing in the inside of the pressure vessel (100) before absorption of the propellant, and wherein p.sub.2 and T.sub.2 are the current pressure and the current temperature in the inside of the pressure vessel (100), V is the volume of the pressure vessel not occupied by the polymer granulate, R.sub.S is the specific gas constant of the gas in the vessel.

11. The method according to claim 1, wherein the mass (m.sub.1) of the propellant initially introduced into the inside of the pressure vessel, or the mass (Δm.sub.a) of the propellant subsequently introduced into the inside of the pressure vessel (100), or the masses (m.sub.1, Δm.sub.a) of the propellant initially and subsequently introduced into the inside of the pressure vessel (100) are determined when the propellant is introduced into the inside of the pressure vessel (100) by means of a mass flow meter (120).

12. The method according to claim 1, wherein the mass (m.sub.1) of the propellant initially introduced into the inside of the pressure vessel, or the mass (Δm.sub.a) of the propellant subsequently introduced into the inside of the pressure vessel (100), or the masses (m.sub.1, Δm.sub.a) of the propellant initially and subsequently introduced into the inside of the pressure vessel (100), or the mass of the polymer granulate arranged in the pressure vessel (100) are determined by means of a balance, a load cell or a force transducer.

13. The method according to claim 1, wherein the gaseous propellant is one of the following gaseous substances or comprises at least one of the following substances: carbon dioxide (CO.sub.2), nitrogen (N.sub.2), argon (Ar), helium (He), a hydrocarbon, butane, pentane, mixtures of one or more gases with CO.sub.2.

14. The method according to claim 1, wherein the polymer granulate (110) contains at least one of the following substances or is formed by one of the following substances: a thermoplastic, a thermosetting plastic, a thermoplastic particle foam, a granulate for producing a thermoplastic particle foam, polypropylene, expanded polypropylene (EPP), polystyrene, expanded polystyrene (EPS).

15. The method according to claim 1, wherein order to terminate the impregnation of the polymer granulate with the propellant, the pressure prevailing in the inside of the pressure vessel (100) is reduced to: an ambient pressure, wherein in particular the amount of propellant released again from the polymer granulate on account of the pressure reduction is determined gravimetrically, or a pressure which is higher than an ambient pressure and at which, in particular, the polymer granulate neither absorbs nor loses any further propellant.

Description

[0083] Further features and advantages of the invention are explained below with reference to the description of the drawings of exemplary embodiments. The following are shown:

[0084] FIGS. 1A and 1B a diagram of the method, in which no additional propellant is added to the pressure vessel,

[0085] FIGS. 2A and 2B a diagram of the method, in which propellant is additionally added to the pressure vessel, the pressure is kept constant and corresponds to the initial pressure, and

[0086] FIGS. 3A and 3B a diagram of the method, in which propellant is additionally added to the pressure vessel, but the pressure has a lower limit and differs from the initial pressure.

[0087] Using the method according to the invention, the end of the impregnation process can be determined by determining the mass of the propellant absorbed by the polymer granulate. A target of the impregnation can be specified, i.e. the degree of loading to be achieved, and the process of impregnation can be discontinued when this target is reached. For this purpose, it is determined in particular how much propellant has currently been absorbed by the polymer granulate by:

1. determining a current temperature in the pressure vessel, as well as a change in pressure in relation to an initial pressure, and/or
2. determining a mass of the propellant which is subsequently added to the pressure vessel.

[0088] FIGS. 1A and 1B illustrate an embodiment of the method according to the invention, in which an initial quantity of propellant gas m.sub.1, for example CO.sub.2, has been introduced into an inside of a pressure vessel 100, in which a polymer granulate 110 is arranged, and a current temperature T.sub.2 in the pressure vessel 100 is determined, as well as a change in pressure in relation to an initial pressure p.sub.1. FIG. 1A shows the state before the start of the impregnation (initial condition), and FIG. 1B shows the state during the impregnation.

[0089] For example, a degree of loading of 2% can be achieved with the aid of the method according to the invention. Th is means that the target is a degree of loading of 2%, and the process can be terminated when or after this target has been reached. A degree of loading of 2% means that the mass of the polymer granulate increases by 2% owing to absorption of the propellant. For example, if polymer granulate having a mass of 100 kg is arranged in the inside of the pressure vessel 100, a mass of 2 kg of the propellant must be absorbed by the polymer granulate 110 for a degree of loading of 2%.

[0090] With the proviso that the general gas equation

p.Math.V=n.Math.R.Math.T

applies, where

[00006]$R_S=\frac{R}{M}$

the following applies:

p.Math.V=m.Math.R.sub.S.Math.T

wherein
m is the mass of the gas, in particular of the propellant,
M is the molar mass of the gas, in particular of the propellant,
R is the universal gas constant, and
R.sub.S is the specific gas constant.

[0091] At the start of the process of impregnation, the propellant, for example CO.sub.2, obeys the equation:

p.sub.1.Math.V=m.sub.1.Math.R.sub.S.Math.T.sub.1

[0092] In this case,

p.sub.1 is the pressure in the inside of the pressure vessel 100 before the start of the absorption process, which pressure can also be referred to as initial pressure, T.sub.1 is the temperature in the inside of the pressure vessel 100 before the start of the absorption process, which temperature can also be referred to as the initial temperature, V is the volume of the propellant in the inside of the pressure vessel 100, wherein the volume V of the propellant in the inside of the pressure vessel can be described as a difference between a volume of the inside of the pressure vessel V.sub.A and a volume of the polymer granulate V.sub.P arranged in the inside, and
R.sub.S is the specific gas constant for which the following applies:

[00007]$R_S=\frac{R}{M}.$

[0093] The initial pressure p.sub.1 and the initial temperature T.sub.1 can be measured, for example, by means of at least one pressure sensor 210 and a temperature sensor 200 in the inside of the pressure vessel 100. The volumes V.sub.A and V.sub.P can be determined so that the volume V of the propellant in the inside of the pressure vessel 100 can be determined. The specific gas constant of the propellant is known or can be calculated.

[0094] This can be used to calculate the mass m.sub.1 by means of the relationship:

[00008]$m_1=\frac{p_{1.Math.}V}{R_S.Math.T_1}.$

[0095] In an alternative embodiment, the mass m.sub.1 can be measured by means of a mass flow meter on introduction into the pressure vessel 100.

[0096] During the impregnation, a current temperature T.sub.2 and a current pressure p.sub.2 in the inside of the pressure vessel 100 are determined. In one embodiment, the current pressure p.sub.2 and the current temperature T.sub.2 are determined continuously. The current pressure p.sub.2 can be measured, for example, by means of at least one pressure sensor 210 in the inside of the pressure vessel 100. The current temperature T.sub.2 can be measured by means of at least one temperature sensor 200 in the inside of the pressure vessel 100.

[0097] During impregnation, at least a portion of the propellant is absorbed by the polymer granulate 110. The current pressure p.sub.2 falls in comparison with the initial pressure p.sub.1. The current temperature T.sub.2 may differ from the initial temperature T.sub.1. The volume of the propellant in the inside of the pressure vessel V remains unchanged in comparison with the volume V of the propellant in the inside of the pressure vessel 100 before the start of the absorption.

[0098] After a certain period of time, in which at least a portion of the propellant has been bound by the polymer granulate 110, the following applies:

p.sub.2.Math.V=m.sub.2.Math.R.sub.S.Math.T.sub.2.

[0099] In this case, the mass m.sub.2 describes the mass of the propellant in the inside of the pressure vessel 100 at the current temperature T.sub.2 and the current pressure p.sub.2 which has not been absorbed by the polymer granulate 110 and can be calculated to give

[00009]$m_2=\frac{p_2.Math.V}{T_2.Math.R_S}.$

[0100] A current mass of the propellant that has been absorbed by the polymer granulate 110, Δm, can easily be calculated using the relationship

Δm=m.sub.1−m.sub.2.

[0101] In one embodiment of the method according to the invention, the current mass of the propellant that has been absorbed by the polymer granulate, Δm, can be determined, in particular dynamically determined, by means of a programmable logic controller. In particular, the programmable logic controller can calculate the current mass Δm from pressure measurements and temperature measurements of the initial variables and the current variables (p.sub.1, p.sub.2, T.sub.1, T.sub.2) that can be provided by the at least one pressure sensor 210 and the at least one temperature sensor 200.

[0102] If the determined value of the current mass Δm corresponds to the target, the process of impregnation may be terminated.

[0103] In the case where the target is a degree of loading of 2% for 100 kg of polymer granulate 100, the impregnation can be terminated when Δm=2 kg is reached.

[0104] FIGS. 2A and 2B illustrate a variant of the method according to the invention, in which an initial quantity of propellant gas m.sub.1, for example CO.sub.2, is introduced into a pressure vessel 100, in which a polymer granulate 110 is arranged, and additional propellant Δm.sub.a is continuously added to the pressure vessel 100, so that the pressure in the inside of the pressure vessel remains constant, i.e., that the current pressure p.sub.2 is equal to the initial pressure p.sub.1. FIG. 2A shows the state before the start of the impregnation (initial condition) and FIG. 2B shows the state during the impregnation.

[0105] As in the method described in FIGS. 1A and 1B, a propellant is introduced into the inside of a pressure vessel 100, and the mass of the initial propellant m.sub.1, the initial temperature T.sub.1, the initial pressure p.sub.1 and the volume V of the propellant gas in the inside of the pressure vessel 100 are determined.

[0106] During the impregnation, the current temperature T.sub.2 and the current pressure p.sub.2 can be measured by means of at least one suitable sensor 200, 210 in the inside of the pressure vessel 100.

[0107] During the impregnation, additional propellant having a mass Δm.sub.a can be added to the inside of the pressure vessel 100.

[0108] In one embodiment of the method, propellant can be added to the inside of the pressure vessel 100 at regular intervals when a difference between the initial pressure p.sub.1 and the current pressure p.sub.2 has an absolute value of more than 0.5 bar. In an alternative embodiment, additional propellant can be added if the one difference between the initial pressure p.sub.1 and the current pressure p.sub.2 has an absolute value of more than 0.3 bar, in particular more than 0.1 bar.

[0109] In an alternative embodiment, additional propellant can be added to the inside of the pressure vessel 100 continuously, in particular using a pressure regulator.

[0110] The addition of the additional propellant can be monitored in particular by means of a programmable logic controller.

[0111] According to one embodiment of the method, the mass Δm.sub.a of the additionally added propellant can be measured by means of a mass flow meter 120. In this case, the mass Δm.sub.a of the additionally added propellant can be composed of a plurality of partial masses, wherein a partial mass of the plurality of partial masses can be introduced into the inside of the pressure vessel 100 at a specific time t. A programmable logic controller can be used to determine the mass Δm.sub.a of the additionally added propellant, in particular from the sum of the plurality of partial masses. When the mass Δm.sub.a of the additionally added propellant has reached the target, the process of impregnation can be terminated. In an embodiment of the method according to the invention, the process of impregnation can be terminated automatically when the target is reached.

[0112] In an alternative embodiment, the mass Δm.sub.a of the additionally added propellant can be determined by determining a total mass. The total mass can be determined using a mass of the pressure vessel, a mass of the polymer granulate arranged in the pressure vessel, and a mass of the propellant gas present in the pressure vessel. The total mass can be determined by means of a balance or a load cell, for example. The total mass can be determined before the start of the impregnation; said mass is also referred to as the initial total mass. Furthermore, a current total mass can be determined, and a difference between the current total mass and the initial total mass can be determined, in particular calculated.

[0113] The mass of the propellant Δm absorbed by the polymer granulate can be determined according to the relationship: Δm=Δm.sub.a−Δm.sub.b wherein Δm.sub.a is the mass of the additionally added propellant and Δm.sub.b describes a change in the mass of the non-absorbed propellant present in the inside of the pressure vessel 100 as a function of the initial temperature T.sub.1 and the current temperature T.sub.2. In other words, Δm.sub.b describes the effect of the temperature on the non-bonded propellant in the inside of the pressure vessel 100.

[0114] From the ideal gas equation, it can be seen that the change in the mass of the non-absorbed propellant in the inside of the pressure vessel Δm.sub.b at a constant pressure (i.e. p.sub.1=p.sub.2) behaves according to the following relationship:

[00010]$\Delta m_b=\frac{p_1.Math.V}{R_S}.Math.\left(\frac{1}{T_2}-\frac{1}{T_1}\right)$

wherein m.sub.1 is the mass of the propellant initially introduced into the inside of the pressure vessel, and wherein T.sub.1 and T.sub.2 are the initial temperature and the current temperature. More accurate results can be achieved by a calculation with the aid of real gas factors, but this is less practice-oriented.

[0115] In a case, in which the current temperature T.sub.2 falls in comparison with the initial temperature T.sub.1, i.e. T.sub.1>T.sub.2, during the process of impregnation, Δm.sub.b assumes a positive value. Less propellant has thus been absorbed by the polymer granulate than would be indicated by an increase in the total mass.

[0116] In an alternative embodiment of the method (FIGS. 3A and 3B), polymer granulate and an initial mass m.sub.1 of a propellant are positioned or introduced in the inside of a pressure vessel 100 as in the methods described above. The initial mass m.sub.1 and initial pressure p.sub.1 and initial temperature T.sub.1 can be determined.

[0117] The total mass, the current temperature T.sub.2 and the current pressure p.sub.2 can be determined during the process of impregnation. Additional propellant Δm.sub.a may be introduced into the inside of the pressure vessel 100, wherein such a mass Δm.sub.a of the additional propellant is introduced that the current pressure p.sub.2 is different from the initial pressure p.sub.1 after the additional introduction. This means that the pressure can drop by a predefined value without being counteracted by adding the propellant. If the current pressure p.sub.2 decreases further, in particular below a predefined threshold value, additional propellant can be introduced. A fall in the efficiency of the impregnation can thus be counteracted. For example, if the current pressure p.sub.2 is too low, the impregnation may take longer than at a higher current pressure p.sub.2.

[0118] The advantage of this method could be that the mass of the non-absorbed propellant m.sub.2 lost after impregnation could be reduced in comparison with the method in which additional propellant is supplied so that the current pressure p.sub.2 is equal to the initial pressure p.sub.1.