GB2226320A - Non-attritive method for making polyethylene particles - Google Patents
Non-attritive method for making polyethylene particles Download PDFInfo
- Publication number
- GB2226320A GB2226320A GB8830075A GB8830075A GB2226320A GB 2226320 A GB2226320 A GB 2226320A GB 8830075 A GB8830075 A GB 8830075A GB 8830075 A GB8830075 A GB 8830075A GB 2226320 A GB2226320 A GB 2226320A
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- GB
- United Kingdom
- Prior art keywords
- particles
- polyethylene
- mixture
- solvent
- moderate
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J3/00—Processes of treating or compounding macromolecular substances
- C08J3/02—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques
- C08J3/03—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques in aqueous media
- C08J3/05—Making solutions, dispersions, lattices or gels by other methods than by solution, emulsion or suspension polymerisation techniques in aqueous media from solid polymers
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J3/00—Processes of treating or compounding macromolecular substances
- C08J3/12—Powdering or granulating
- C08J3/14—Powdering or granulating by precipitation from solutions
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/28—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof by elimination of a liquid phase from a macromolecular composition or article, e.g. drying of coagulum
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2201/00—Foams characterised by the foaming process
- C08J2201/04—Foams characterised by the foaming process characterised by the elimination of a liquid or solid component, e.g. precipitation, leaching out, evaporation
- C08J2201/052—Inducing phase separation by thermal treatment, e.g. cooling a solution
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
- C08J2323/02—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers not modified by chemical after treatment
- C08J2323/04—Homopolymers or copolymers of ethene
- C08J2323/06—Polyethene
Abstract
A non-attritive method for making fine particles of polyethylenes comprises heating a mixture of the polyethylene in a moderate solvent for the polyethylene to a temperature above the melting point of the polyethylene when in the moderate solvent and then cooling whereupon the particles re-crystallise from the mixture. The particles comprise crystalline zones and amorphous zones containing imbibed solvent and may be used in coating, in coating compositions and in making porous particles.
Description
NON-ATTRITIVE METHOD FOR MASKING POLYETHYLENE
PARTICLES, PARTICLES OBTAINABLE BY THE METHOD
AND THEIR USE
This invention relates to a non-attritive method for making distinct fine particles of partially crystalline polyethylene polymers (including copolymers of ethylene with up to 30 wt% of other alpha-olefins or olefinically unsaturated carboxylic acids or esters such as vinyl acetate or lower (for examples C1 to C4) alkyl acrylates or methacrylates) to novel particles obtainable by the method and to the use of the particles, especially in coating processes and compositions.
Polyethylenes are well known thermoplastics. A fuller description of the various types of polyethylene is given in Volume 16 of the third edition of Kirk-Othmer's "Encyclopaedia of Chemical
Technology" Volume 16 published by John Wiley & Sons of New York in 1981 (see pages 402 to 441) the contents of which are herein incorporated by reference. They exist as low density (sometimes called branched) forms made by free radical polymerisation at high pressures or by metal catylsed copolymerisation with longer chain (C4 to C10) alpha-olefins. They also exist as high density forms made by Ziegler polymerisation and other metal catylsed polymerisations.
The commercial manufacture of polyethylenes by the free radical process produces pellets which usually have a maximum dimension of at least about 2mm. For some purposes such as powder coating or addition to coating compositions, the pellets need to be converted into distinct fine particles, that is to say particles having a maximum dimension of below 500m. Hitherto this has been done by attritive methods such as grinding or milling. However attritive methods produce particles of an unpredictable shape which are therefore inconvenient to use in coating processes and compositions and the particles are also totally solid which is sometimes a disadvantage.The manufacture of polyethylene by metal catalysed processes produces fine particles of polyethylene which are also totally solid and which are usually converted to pellets having a maximum dimension of at least 2mm for many commercial uses.
An object of this invention is to provide a non-attritive method for making distinct fine particles of partially crystalline polyethylene.
Another object is to provide novel fine particles of a less unpredictable shape which are partially plasticised and which are amongst other things especially suitable for use in coating processes and compositions. A further object is to provide a process for coating surfaces in which such novel particles are used.
Accordingly this invention provides a non-attritive method for making distinct particles of partially crystalline polyethylene wherein the method comprises a) heating a mixture comprising a moderate solvent
for the polyethylene and at least 5 (preferably
10 to 60) wt% of the polyethylene (the
percentage being based on the combined weights
of the moderate solvent and the polyethylene) to
a temperature above the crystalline melting
point (Tm) of the polyethylene when in mixture
and preferably to a temperature in the range
Tm + 10 C to Tm + 40 C and b) cooling the heated mixture under conditions such
that solid/liquid phase separation occurs whereby distinct particles of polyethylene are produced. Usually the particles have a number average maximum dimension of from 0.1 to 100cm.
It is essential to use a moderate solvent for if a good solvent is used with the concentrations of polyethylene employed in the performance of this invention, then the polyethylene either fails to come out of solution or comes out either as a gel, agglomerate or as particles of unpredictable shape.
A "moderate solvent" is a solvent which depresses the crystalline melting point Tm of the polyethylene by not more than 80"C when the polyethylene constitutes 30 wt % of a mixture of moderate solvent and polyethylene. Crystalline melting point is determined by differential scanning calorimetry performed in turn on the polyethylene alone and on the above mixture. The mixture must be contained in a sealed capsule to prevent loss of the moderate solvent during heating. More particularly, 10mug of polyethylene alone and 10mug of mixture are each in turn subjected to cycles of heating and cooling performed under nitrogen in the calorimeter.Each heating/cooling cycle comprises heating the sample under test (which may be polyethylene alone or a mixture) at a rate of 200cumin to cause crystalline melting which occurs at a temperature Tm, subsequently holding the sample for two minutes at a holding temperature Th which is above Tm, then cooling at a rate of 200cumin to cause recrystallisation which occurs at a temperature Tc and finally continuing cooling to a temperature of at least 100C below Tc Tm and Tc are detected respectively as an endothermic trough and an exothermic peak in the graph of heat absorbed or evolved versus temperature. Each cycle is repeated to discover whether a consistent value for Tc can be obtained.If consistency is not obtained, another pair of heating/cooling cycles are performed using a slightly higher Th. Further pairs of cycles with gradually increasing Th are performed until consistent values for Tc are achieved whereupon the pair of cycles which gave consistent values is repeated and the value for Tm obtained is defined to be the crystalline melting point of the sample under test. A good solvent for polyethylene such as depresses the melting point by well in excess of 800C whereas moderate solvents such as certain aliphatic hydrocarbons having a boiling point of from 200 to 250"C at 1 bar or decahydronapthalene depress the melting point of low density polyethylene by only 30"C and 340C respectively and of high density polyethylene by only 5"C and 22"C respectively.
It is also important when performing the method of this invention that the mixture be heated to above the melting point of the polyethylene when in the mixture (Tm) for otherwise there will be obtained particles of unpredictable shape comprising some undissolved polyethylene and some re-crystallised polyethylene agglomerated onto the undissolved polyethylene.Preferably the mixture should be heated at least to its clearing temperature "Tc1,, The "clearing temperature" (TCl) of any chosen mixture comprising dry moderate solvent and dried polyethylene is the temperature at which the appearance of the mixture becomes clear to the unaided eye. TCl is determined by heating 2g of a chosen mixture until the polyethylene dissolves and the initially turbid solution obtained turns clear for a first time, then cooling the mixture to room temperature an finally re-heating the mixture until it turns clear for the second time. The temperature at which it turns clear for the second time is defined to be the clearing temperature (Tcl) for that mixture. Heating to TCl and above (preferably to 10 to 30 C above Tcl) leads to the formation of more uniform prticle sizes. Uniformity of particle size is also enhanced by heating the mixture to a holding temperature Th which is above Tm for the polyethylene when in the mixture (and preferably 10 to 40 C above) and holding the mixture at temperature Th for from 1 to 30 minutes although holding for 1 to 5 minutes is usually sufficient.
It has been found that some large pellets of polyethylene available commercially can be inconveniently slow to dissolve. Where time saving is important, this problem can be alleviated by using a pre-heating and pre-cooling cycle as follows. The mixture is first pre-heated to a temperature above the melting point of the pure polyethylene, for example to 220"C. Such pre-heating causes a rapid dissolution of the polyethylene. The mixture is then pre-cooled to at least a temperature (for example 30 to 80"C below the melting point of the pure polymer or lower) so that polyethylene re-solidifies from the mixture.Such re-solidification produces polyethylene in a form which dissolves quickly (usually within 2 minutes) on heating to Tm or above so producing a mixture consisting of a solution of polyethylene in moderate solvent which appears clear to the unaided eye.
In performing the process of this invention it is essential to employ conditions which cause solid/liquid phase separation to occur from the mixture when it is in its solution state for otherwise an agglomerated mass will be obtained. To achieve solid/liquid phase separation, it is necessary to use a moderate solvent, to use a mixture containing at least 5 wt% of polyethylene and to avoid shock cooling which usually means cooling at a rate of no faster than 3000C/min. The preferred cooling rates are from 100C/min to 50 C/min. It is also preferred to stir the mixture during cooling.
Stirring promotes greater uniformity of particle size.
This invention also provides distinct fine particles of partially crystalline polyethylene wherein the particles comprise zones of crystalline polyethylene and the particles are partially plasticised in that they also comprise zones of amorphous polyethylene containing imbibed moderate solvent. Generally the particles will comprise from 10 to 90 (more usually from 40 to 75) wt% of imbibed moderate solvent. Usually large proportions of imbibed solvent and amorphous polymer are favoured by performing the method of this invention using high cooling rates (say 100 to 3000C/min). The particles are obtainable by the method of this invention as a slurry or paste in the moderate solvent.
Alternatively the particles can be obtained in a free flowable condition by removal of the solvent external of the particles by for example rinsing with a liquid miscible with the moderate solvent but which does not dissolve the polyethylene. Methanol, ethanol and aliphatic ketones, for example methyl ethyl ketone, are examples of such a liquids.
The size of the particles can be adjusted by by varying the cooling rates employed in the method or by incorporating nucleating agents into the polyethylene. In general higher cooling rates and also nucleating agents favour smaller particles sizes. Typical nucleating agents for polyethylenes include talc and sodium benzoate. The uniformity of particle size increases as the temperature to which the mixture is heated is increased towards Tm + 400C.
No advantage is generally gained by using temperatures above Tm + 40"C and of course temperatures high enough to cause thermal degradation of the polyethylene should be avoided. Use of nucleating agents also improves uniformity of particle size.
The presence of a nucleating agent may cause a residual turbidity to persist at Tcl However the skilled eye is able to distinguish between turbidity caused by the polyethylene and that caused by a nucleating agent and so the determination of Tcl and clearing are not unduly hindered.
The shape of the particles obtained varies with the concentration of polyethylene in the mixture.
Lower concentrations favour flaky or rod-like particles whilst higher concentrations favour approximately spherical or oblate particles. Usually concentrations of at least 10 wt % should be used to obtain spherical or oblate particles with the best results being obtained with concentrations above 25 wt %.
It has been discovered that the presence of imbibed moderate solvent in the particles of this invention enhances their ability to flow and coalesce when heated so as to provide a continuous layer of polyethylene. Accordingly this invention also provides a process for coating a surface with polyethylene which process comprises a) applying a covering of particles (usually
evenly) across the surface and b) heating the particles to cause them to coalesce wherein the particles comprise zones of crystalline polyethylene and the particles employed are partially plasticised in that they also comprise zones of amorphous polyethylene containing imbibed moderate solvent.Preferably the particles are applied to the surface as a dispersion of usually 5 to 35 (especially 10 to 25) wt % of particles in either moderate solvent or a liquid which is not a solvent for the polyethylene, for example methyl or ethyl alcohol or an aliphatic ketone or an aqueous surfactant. Preferably the particles are heated to a temperature of from 150 to 2000C for low density polyethylene, 200"C to 240"C for high density polyethylenes and for a period of from 2 to 30 minutes. The surfaces may be metal for example aluminium, stainless steel or non-metallic, for example glass. Polyethylenes containing a small amount (for example up to 1 wt%) of copolymerised olefinically unsaturated carboxylic acid are especially useful for coating metals.In particular the particles may be used to coat sheets and shaped articles such as cans and fire extinguishers for example in conventional powder coating operations.
The particles (especially the flaky or rod-like particles) may also be used to impregnate continuous rovings of a wide variety of fibres including glass and carbon fibres. If the impregnated fibres are heated to soften or melt the particles, they may be compressed to produce a composite which on cooling comprises fibre consolidated in polyethylene.
It also has been found that the particles according to this invention disperse well in coating compositions (for example paints and varnishes) based on both water or organic solvents. Generally the assistance of a surfactant is needed to obtain the best dispersions in water-based paints. Accordingly this invention provides a coating composition (which may be based on an organic solvent or water) and comprising a binder of a type used in coating compositions and (from for example 0.5 to 50 wt % of) particles of polyethylene wherein the particles of polyethylene comprise zones of crystalline polyethylene and the particles are partially plasticised in that they also comprise zones of amorphous polyethylene containing imbibed moderate solvent.Typical binders for coating compositions are described in the third edition of the book "Introduction to Paint Chemistry and Principles of
Paint Technology" by G P A Turner and published by
Chapman and Hall of London in 1988, the contents of which are herein incorporated by reference. The coating composition may also comprise pigments and extenders and other conventional ingredients described in the above book.
Particles made according to the method of this invention may be converted to porous particles by extraction of the imbibed moderate solvent.
Accordingly this invention provides a process for making porous particles of polyethylene wherein particles of polyethylene comprising zones of crystalline polyethylene and which particles are partially plasticised in that they also comprise zones of amorphous polyethylene containing imbibed moderate solvent are immersed in a liquid extractant which is miscible with the moderate solvent but which is not a solvent for the crystalline polyethylene until moderate solvent has been extracted into the extractant and then the extractant is washed from the particles. Particles having small pores can be obtained by using extractants such as acetone, methyl or ethyl alcohol which only extract the moderate solvent.Porous particles may be used to increase the opacity of coating compositions or they may be applied to surfaces by conventional powder coating techniques or by electrostatic spraying.
The invention is further illustrated by the following Examples.
EXAMPLES 1 TO 8
Making the Particles:
Various polyethylenes available from BP
Chemicals Ltd ("Novex" LD 1302 AA low density polyethylene or "Rigidex" HM 5590 EA high density polyethylene) were each mixed with a moderate solvent in amounts all as specified in Table 1. 10g of each mixture was subjected to a double pre-heating/pre-cooling cycle and then heated to a temperature above the crystalline melting point of the polyethylene when in the solvent and also above the clearing temperature for the mixture. The mixture was then allowed to cool to room temperature.
The temperatures reached in these heating cycles are given in Table 2. Heating caused the polyethylene to dissolve whereupon the mixture existed as a solution.
At least the last cooling caused a solid/liquid phase separation and re-crystallisation which produced fine, distinct and partially plasticised particles comprising crystalline zones
TABLE 1
I I I I Eg Solvent Type Amount Typical of PE PE Particle | | in Mix- Dimension ture, #m wt % II I 1 *"Exxol" D200/240 LPDE 10 12 to 15 2 " " " 30 12 to 15 3 " " HDPE 10 30 4 " " " 30 30 5 Decahydro LPDE 10 25 I I naphthalene I I I 6 " " 30 30 7 " HDPE 10 12 to 15 8 " " 30 30 *Exxol" D200/240 which is a de-aromatised hydrocarbon having a boiling point of from 204 to 2450C at 1 bar.
TABLE 2
HEATING CYCLES
I I I I I PE 1st Cool to 2nd Cool to Heat to Pre-Heat C Pre-Heat C C to C to C LPDE 210 30 105 30 100 HDPE 210 25 170 25 170 and amorphous zones containing imbibed solvent. In the case of the low density polyethylene particles a little light shearing (for example by rolling between finger and thumb) was needed to separate the particles. The particles were either spherical or oblate having a typical maximum dimension as determined by optical microscope as shown in Table 1.
The particles comprised about 50 wt % of imbibed solvent and were obtained as a paste consisting of particles and moderate solvent.
The pastes obtained could be converted to dry free flowing particles by rinsing with acetone.
Rinsing amounted to placing the paste on filter paper in a funnel and pouring acetone through for 30 seconds at room temperature.
Claims (21)
1. A non-attritive method for making distinct particles of partially crystalline polyethylene wherein the method comprises a) heating a mixture comprising a moderate solvent
for the polyethylene and at least 5 wt % of the
polyethylene (the percentage being based on the
combined weights of the moderate solvent and the
polyethylene) to a temperature above the
crystalline melting point (Tm) of the
polyethylene when in the mixture and b) cooling the heated mixture under conditions such
that solid/liquid phase separation occurs whereby distinct particles of polyethylene are produced.
2. A method according to Claim 1 wherein the mixture comprises from 10 to 60 wt % of the polyethylene.
3. A method according to Claim 1 or Claim 2 wherein the moderate solvent is chosen from aliphatic hydrocarbons having a boiling point of from 200 to 250"C at 1 bar or decahydronapthalene.
4. A method according to any one of Claims 1 to 3 wherein the mixture is cooled at a rate of less than 300"C/min.
5. A method according to any one of Claims 1 to 4 wherein the mixture is cooled at a rate of 10 to 50 C/min.
6. A method according to any one of Claims 1 to 4 wherein the mixture is cooled at a rate of 100 to 300"C/min.
7. A method according to any one of the preceding
Claims wherein the mixture is heated to a temperature of from Tm + 10 C to Tm + 40 C.
8. A method according to any one of Claims 1 to 6 wherein the mixture is heated to at least its clearing temperature (TCl).
9. A method according to Claim 8 wherein the mixture is heated to a temeprature of from T + 10 to TCl + 300C.
10. A method according to any one of the preceding
Claims wherein the mixture is heated to a holding temperature (Th) which is above Tm and the mixture is held at temperature Th for from 1 to 30 minutes before cooling occurs.
11. A method according to any one of the preceding
Claims wherein the particles obtained are converted to a free flowable condition by removal of the moderate solvent external of the particles.
12. Distinct fine particles of partially crystalline polyethylene wherein the particles comprise zones of crystalline polyethylene and the particles are partially plasticised in that they also comprise zones of amorphous polyethylene containing imbibed moderate solvent.
13. Particles according to Claim 12 wherein the particles comprises from 40 to 75 wt % of imbibed solvent.
14. Particles according to Claim 12 or Claim 13 wherein the particles have a number average maximum diameter of from 0.1 to 100cm.
15. A process for coating a surface, which process comprises a) applying a covering of particles across the
surface and b) heating the particles to cause them to coalesce
wherein the particles employed comprise zones of
crystalline polyethylene and the particles are
partially plasticised in that they also comprise
zones of amorphous polyethylene containing
imbibed moderate solvent.
16. A process according to Claim 15 wherein the particles are applied to the surface as a dispersion comprising from 5 to 35 wt % of particles in liquid.
17. A process according to Claim 16 wherein the liquid is an aqueous surfactant.
18. A coating composition based on a solvent and comprising a binder of a type used in coating compositions and wherein the particles of polyethylene comprise zones of crystalline polyethylene and are the particles are partially in that they also comprise zones of amorphous polyethylene containing imbibed moderate solvent.
19. A coating composition according to Claim 18 wherein the solvent is water.
20. A coating composition according to Claim 18 wherein the solvent is an organic solvent.
21. A process for making porous particles of polyethylene wherein particles of polyethylene comprising zones of crystalline polyethylene and the particles are partially plasticised in that they also comprise zones of amorphous polyethylene containing imbibed moderate solvent, are immersed in a liquid extractant which is miscible with the moderate solvent but which is not a solvent for the crystalline polyethylene until moderate solvent has been extracted into the extract ant and then the extractant washed from the particles.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8830075A GB2226320A (en) | 1988-12-23 | 1988-12-23 | Non-attritive method for making polyethylene particles |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8830075A GB2226320A (en) | 1988-12-23 | 1988-12-23 | Non-attritive method for making polyethylene particles |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8830075D0 GB8830075D0 (en) | 1989-02-22 |
| GB2226320A true GB2226320A (en) | 1990-06-27 |
Family
ID=10649038
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8830075A Withdrawn GB2226320A (en) | 1988-12-23 | 1988-12-23 | Non-attritive method for making polyethylene particles |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2226320A (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5290913A (en) * | 1992-10-08 | 1994-03-01 | Carrier Vibrating Equipment, Inc. | Method and apparatus for the heat treatment of material |
| WO1997020884A1 (en) * | 1995-12-06 | 1997-06-12 | Dsm N.V. | Process for the preparation of porous polyolefin particles |
| WO1998004618A1 (en) * | 1996-07-27 | 1998-02-05 | Solvay Deutschland Gmbh | Process for producing porous polymer globules |
| EP0849312A1 (en) * | 1996-12-19 | 1998-06-24 | Paraffinwerk Webau GmbH | Process for recovering polyolefins from polymer compositions or from waste materials |
| WO1998055540A1 (en) * | 1997-06-05 | 1998-12-10 | Dsm N.V. | Process for preparing porous polyolefin particles |
-
1988
- 1988-12-23 GB GB8830075A patent/GB2226320A/en not_active Withdrawn
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5290913A (en) * | 1992-10-08 | 1994-03-01 | Carrier Vibrating Equipment, Inc. | Method and apparatus for the heat treatment of material |
| WO1997020884A1 (en) * | 1995-12-06 | 1997-06-12 | Dsm N.V. | Process for the preparation of porous polyolefin particles |
| US6051618A (en) * | 1995-12-06 | 2000-04-18 | Dsm N.V. | Process for the preparation of porous polyolefin particles |
| WO1998004618A1 (en) * | 1996-07-27 | 1998-02-05 | Solvay Deutschland Gmbh | Process for producing porous polymer globules |
| EP0849312A1 (en) * | 1996-12-19 | 1998-06-24 | Paraffinwerk Webau GmbH | Process for recovering polyolefins from polymer compositions or from waste materials |
| WO1998055540A1 (en) * | 1997-06-05 | 1998-12-10 | Dsm N.V. | Process for preparing porous polyolefin particles |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8830075D0 (en) | 1989-02-22 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |