GB1603638A - Polymer processing - Google Patents

Polymer processing Download PDF

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Publication number
GB1603638A
GB1603638A GB2964177A GB2964177A GB1603638A GB 1603638 A GB1603638 A GB 1603638A GB 2964177 A GB2964177 A GB 2964177A GB 2964177 A GB2964177 A GB 2964177A GB 1603638 A GB1603638 A GB 1603638A
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GB
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Prior art keywords
polymer
cross
linking
irradiation
method
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Expired
Application number
GB2964177A
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Bowman J
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Classifications

    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08JWORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G
    • C08J3/00Processes of treating or compounding macromolecular substances
    • C08J3/24Crosslinking, e.g. vulcanising, of macromolecules
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE, IN GENERAL
    • B29BPREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
    • B29B9/00Making granules
    • B29B9/16Auxiliary treatment of granules
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B29WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE, IN GENERAL
    • B29CSHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C45/00Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
    • B29C45/0001Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor characterised by the choice of material
    • CCHEMISTRY; METALLURGY
    • C08ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08JWORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G
    • C08J3/00Processes of treating or compounding macromolecular substances
    • C08J3/28Treatment by wave energy or particle radiation
    • DTEXTILES; PAPER
    • D01NATURAL OR ARTIFICIAL THREADS OR FIBRES; SPINNING
    • D01FCHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
    • D01F6/00Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof
    • D01F6/02Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • D01F6/04Monocomponent artificial filaments or the like of synthetic polymers; Manufacture thereof from homopolymers obtained by reactions only involving carbon-to-carbon unsaturated bonds from polyolefins

Description

(54) POLYMER PROCESSING (71) I, JEREMY ARCHIBALD BOWMAN, a British subject of Brunel University, Uxbridge, Middlesex, do hereby declare this invention, for which I pray that a patent may be granted to me. and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to the processing of thermoplastic polymers, in particular of amorphous or semi-crystalline thermoplastic polymers.

In the manufacture of finished articles from thermoplastic polymers, it is known to cross-link the polymer after fabrication. The fabricated polymer may be cross-linked by irradiation or by chemical cross-linking. In the case of chemical cross-linking, a cross-linking agent, which is insensitive to the fabrication conditions, is compounded with the polymer prior to fabrication and the fabricated polymer is, for example, heated to a sufficiently high temperature to generate cross-linking.

According to the present invention there is provided a method of processing an amorphous or semi-crystalline thermoplastic polymer which method comprises crosslinking the polymer in particulate form and fabricating the so-crosslinked polymer by injection moulding or fibre spinning such that there is obtained a fabricated polymer of enhanced tensile strength.

During the injection moulding of fibre spinning of the fabrication step there is introduced significant preferred orientation into the polymer before crystallisation or freezing to preserve that orientation. In particular. there may be introduced significant orientation into the melt which is preserved by shock cooling.

It has surprisingly been found that, with cross-linking of the amorphous or semicrystalline thermoplastic polymer in particulate form prior to its fabrication, there may be obtained a fabricated polymer of higher tensile strength than when the same polymer is fabricated in conventional manner without the prior cross-linking.

It is also found that the method of the invention can lead to increase in stiffness or in environmental stress crack resistance of the polymer.

The thermoplastic polymer suitable for use in accordance with the process of the present invention is amorphous or semi-crystalline (which latter can be cross-linked at either low or high degrees or perfection), homo- or copolymeric, or may comprise a filler. In particular the thermoplastic polymer is as-received polymer and may be virgin polymer (i.e.

unprocessed polymer) or regrind polymer (i.e. polymer which has been previously processed and reclaimed for recycling). In the case of regrind polymer there tends to have been some molecular degradation leading to a lowering of tensile strength. Thus the method of the invention offers a means to reverse this degradation.

Generally the polymer is used in the form of granules or powder.

The thermoplastic polymer is suitably a high density polyethylene (HDPE).

The cross-linking of the thermoplastic polymer in accordance with the method of the present invention may be effected by irradiation and/or by chemical cross-linking, for example using an organic peroxide such as one of the Retilox or Di-Cup type: p - C6H4 [C(C113)2O-O-C(C113)3]2 or C6H5(CH3)2C-O-O-C(CH3)2C6H respectively. [Retilox and Di-Cup are Registered Trade Marks].

The chemical cross-linking agent may be compounded with the polymer for example a Banbury blender or a two roll mill. The cross-linking agent may then be exposed to those temperatures, and for those times, which permit the requireddegree of cross-linking. The resulting crepe will then consist of the cross-linked polymer which can next be fabricated.

Cross-linking by irradiation is, however, generally to be preferred, particularly for those applications requiring minimum polymer contamination. Irradiation may be effected by electron beam or y - radiation (for example using a cobalt-60 source), desirably at a temperature which avoids significant fusion of the granules or powder.

The amount of cross-linking introduced must neither be so small as to give an insignificant improvement in tensile strength nor so large as to prevent the fabriction.

Cross-linking may rapidly reduce the melt flow index (MFI) of the polymer leading to incomplete mould filling (in injection moulding) or other fabrication failures.

Accordingly, it is preferred that for successful operation of the method of the present invention the as-received polymer should have a high MFI thereby enabling higher cross-linking without fabrication difficulties arising. (Lower molecular weight polymers generally have a higher MFI but will be more prone to relaxation effects so that their quenching must be more extreme). Where cross-linking is effected by irradiation, it is generally found that doses of up to 50M Rads, typically up to 10M Rads and preferably from 0.5 to 2.0M Rads can be used.

Fabriction conditions are those which introduce and preserve significant preferred orientation (which includes molecular, crystalline and filler orientation). In the case of injection moulding these are low injection speed, low melt temperature, low mould temperature and high packing pressure. In the case of fibre spinning these are low melt temperature, fast cooling and high take off speed.

In particular the present invention provides a method of processing high density polyethylene which method comprises cross-linking high density polyethylene in particulate form by irradiation with 0.2 to 2.5M Rads and fabricating the so-crosslinked polymer by injection moulding or fibre spinning such that there is obtained a fabricated polymer of enhanced tensile strength.

The following Example illustrates the invention.

Example A homopolymeric HPDE (Rigidex 140/60 ex BP; Mw = 65,000; MW/Mn = 4.6; MFI as received 11.8) was irradiated at room temperature as granules with doses of 0.2, 0.5, 1.02, 2.0, 5.0 and 10.0M Rad (from a cobalt 60 source typically at 0.5M Rad/hour). The irradiated granules were then injection moulded using a wide range of barrel temperatures (150 to 250"C) with the mould temperature (40"C), injection pressure (41.1 MNm-2) and cycle times (fill times, 2.5 sec), hold-on pressure time (12.5 sec), cooling time (20 sec) and mould open time (5 sec) remaining constant, to produce a dumb-bell type tensile bar. (For granules irradiated to 5.0M Rad and above, incomplete mould filling occurred at all barrel temperatures while the 2.0M Rad irradiated sample was not mouldable at barrel temperatures of 1500C and 175"C).

The as-moulded tensile bars were next tested in uniaxial tension at room temperature at a cross-head speed of 0.5 mm/min.

Figure 1 of the accompanying drawings shows the marked reduction of MFI with increasing radiation dose, 2.5M Rad being identified as the maximum dose that this particular polymer could usefully sustain in the method of the present invention.

Figure 2 of the accompanying drawings shows the increase in strength of the tested tensile bars at different barrel temperatures. It will be seen that the tensile strength of the bars increases markedly with increasing dose, for a given barrel temperature; and that, for a given dose, raising the barrel temperature tends to reduce the effect.

WHAT I CLAIM IS: 1. A method of processing an amorphous or semi-crystalline thermoplastic polymer which method comprises cross-linking the polymer in particulate form and fabricating the so-crosslinked polymer by injection moulding or fibre spinning such that there is obtained a fabricated polymer of enhanced tensile strength.

2. A method according to claim 1 wherein the cross-linking is effected by irradiation of the polymer with up to 10M Rads.

3. A method according to claim 2 wherein the irradiation is effected with electron beam or y-radiation.

4. A method according to claim 1 wherein the polymer is chemically cross-linked.

5. A method according to claim 4 wherein an organic peroxide is used as chemical cross-linking agent.

6. A method according to any one of claims 1 to 5 wherein the polymer is a high density polyethylene.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (9)

**WARNING** start of CLMS field may overlap end of DESC **. The chemical cross-linking agent may be compounded with the polymer for example a Banbury blender or a two roll mill. The cross-linking agent may then be exposed to those temperatures, and for those times, which permit the requireddegree of cross-linking. The resulting crepe will then consist of the cross-linked polymer which can next be fabricated. Cross-linking by irradiation is, however, generally to be preferred, particularly for those applications requiring minimum polymer contamination. Irradiation may be effected by electron beam or y - radiation (for example using a cobalt-60 source), desirably at a temperature which avoids significant fusion of the granules or powder. The amount of cross-linking introduced must neither be so small as to give an insignificant improvement in tensile strength nor so large as to prevent the fabriction. Cross-linking may rapidly reduce the melt flow index (MFI) of the polymer leading to incomplete mould filling (in injection moulding) or other fabrication failures. Accordingly, it is preferred that for successful operation of the method of the present invention the as-received polymer should have a high MFI thereby enabling higher cross-linking without fabrication difficulties arising. (Lower molecular weight polymers generally have a higher MFI but will be more prone to relaxation effects so that their quenching must be more extreme). Where cross-linking is effected by irradiation, it is generally found that doses of up to 50M Rads, typically up to 10M Rads and preferably from 0.5 to 2.0M Rads can be used. Fabriction conditions are those which introduce and preserve significant preferred orientation (which includes molecular, crystalline and filler orientation). In the case of injection moulding these are low injection speed, low melt temperature, low mould temperature and high packing pressure. In the case of fibre spinning these are low melt temperature, fast cooling and high take off speed. In particular the present invention provides a method of processing high density polyethylene which method comprises cross-linking high density polyethylene in particulate form by irradiation with 0.2 to 2.5M Rads and fabricating the so-crosslinked polymer by injection moulding or fibre spinning such that there is obtained a fabricated polymer of enhanced tensile strength. The following Example illustrates the invention. Example A homopolymeric HPDE (Rigidex 140/60 ex BP; Mw = 65,000; MW/Mn = 4.6; MFI as received 11.8) was irradiated at room temperature as granules with doses of 0.2, 0.5, 1.02, 2.0, 5.0 and 10.0M Rad (from a cobalt 60 source typically at 0.5M Rad/hour). The irradiated granules were then injection moulded using a wide range of barrel temperatures (150 to 250"C) with the mould temperature (40"C), injection pressure (41.1 MNm-2) and cycle times (fill times, 2.5 sec), hold-on pressure time (12.5 sec), cooling time (20 sec) and mould open time (5 sec) remaining constant, to produce a dumb-bell type tensile bar. (For granules irradiated to 5.0M Rad and above, incomplete mould filling occurred at all barrel temperatures while the 2.0M Rad irradiated sample was not mouldable at barrel temperatures of 1500C and 175"C). The as-moulded tensile bars were next tested in uniaxial tension at room temperature at a cross-head speed of 0.5 mm/min. Figure 1 of the accompanying drawings shows the marked reduction of MFI with increasing radiation dose, 2.5M Rad being identified as the maximum dose that this particular polymer could usefully sustain in the method of the present invention. Figure 2 of the accompanying drawings shows the increase in strength of the tested tensile bars at different barrel temperatures. It will be seen that the tensile strength of the bars increases markedly with increasing dose, for a given barrel temperature; and that, for a given dose, raising the barrel temperature tends to reduce the effect. WHAT I CLAIM IS:
1. A method of processing an amorphous or semi-crystalline thermoplastic polymer which method comprises cross-linking the polymer in particulate form and fabricating the so-crosslinked polymer by injection moulding or fibre spinning such that there is obtained a fabricated polymer of enhanced tensile strength.
2. A method according to claim 1 wherein the cross-linking is effected by irradiation of the polymer with up to 10M Rads.
3. A method according to claim 2 wherein the irradiation is effected with electron beam or y-radiation.
4. A method according to claim 1 wherein the polymer is chemically cross-linked.
5. A method according to claim 4 wherein an organic peroxide is used as chemical cross-linking agent.
6. A method according to any one of claims 1 to 5 wherein the polymer is a high density polyethylene.
7. A method of processing high density polyethylene which method comprises
cross-linking high density polyethylene in particulate form by irradiation with 0.2 to 2.5M Rads and fabricating the so-crosslinked polymer by injection moulding or fibre spinning such that there is obtained a fabricated polymer of enhanced tensile strength.
8. A method according to claim 7 substantially as described in the Example.
9. Polymer processed by the method claimed in any one of the preceding claims.
GB2964177A 1978-05-31 1978-05-31 Polymer processing Expired GB1603638A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB2964177A GB1603638A (en) 1978-05-31 1978-05-31 Polymer processing

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB2964177A GB1603638A (en) 1978-05-31 1978-05-31 Polymer processing

Publications (1)

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GB1603638A true true GB1603638A (en) 1981-11-25

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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0124722A2 (en) * 1983-03-14 1984-11-14 Phillips Petroleum Company Polymer composition and preparation method
WO1985005316A1 (en) * 1984-05-11 1985-12-05 Stamicarbon B. V. Heat shrinkable material and articles
EP0215507A1 (en) * 1985-08-21 1987-03-25 Stamicarbon B.V. Process for producing polyethylene articles having a high tensile strength and modulus
EP0238447A2 (en) * 1986-03-21 1987-09-23 Ciba-Geigy Ag Method for producing a temperature and crack resistant plastics material
US5160464A (en) * 1983-12-09 1992-11-03 National Research Development Corporation Polymer irradiation
WO2000018995A2 (en) * 1998-09-30 2000-04-06 Kimberly-Clark Worldwide, Inc. Crimped polymeric fibers and nonwoven webs made therefrom with improved resiliency
WO2010105981A1 (en) * 2009-03-18 2010-09-23 Baumhueter Extrusion Gmbh Polyethylene fiber, its use and process for its manufacture
US10000587B2 (en) 2012-08-31 2018-06-19 Baumhueter Extrusion Gmbh Cross-linked polyethylene fiber, its use and process for its manufacture

Cited By (16)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0124722A2 (en) * 1983-03-14 1984-11-14 Phillips Petroleum Company Polymer composition and preparation method
EP0124722A3 (en) * 1983-03-14 1986-07-02 Phillips Petroleum Company Polymer composition and preparation method
US5160464A (en) * 1983-12-09 1992-11-03 National Research Development Corporation Polymer irradiation
WO1985005316A1 (en) * 1984-05-11 1985-12-05 Stamicarbon B. V. Heat shrinkable material and articles
EP0164779A1 (en) * 1984-05-11 1985-12-18 Stamicarbon B.V. Heat shrinkable material and articles
EP0167187A1 (en) * 1984-05-11 1986-01-08 Stamicarbon B.V. Novel irradiated polyethylene filaments, tapes and films and process therefor
US5066755A (en) * 1984-05-11 1991-11-19 Stamicarbon B.V. Novel irradiated polyethylene filaments tapes and films and process therefor
EP0215507A1 (en) * 1985-08-21 1987-03-25 Stamicarbon B.V. Process for producing polyethylene articles having a high tensile strength and modulus
EP0238447A3 (en) * 1986-03-21 1989-03-15 Ciba-Geigy Ag Method for producing a temperature and crack resistant plastics material
EP0238447A2 (en) * 1986-03-21 1987-09-23 Ciba-Geigy Ag Method for producing a temperature and crack resistant plastics material
WO2000018995A2 (en) * 1998-09-30 2000-04-06 Kimberly-Clark Worldwide, Inc. Crimped polymeric fibers and nonwoven webs made therefrom with improved resiliency
WO2000018995A3 (en) * 1998-09-30 2000-05-25 Kimberly Clark Co Crimped polymeric fibers and nonwoven webs made therefrom with improved resiliency
US6528439B1 (en) 1998-09-30 2003-03-04 Kimberly-Clark Worldwide, Inc. Crimped polymeric fibers and nonwoven webs made therefrom with improved resiliency
WO2010105981A1 (en) * 2009-03-18 2010-09-23 Baumhueter Extrusion Gmbh Polyethylene fiber, its use and process for its manufacture
CN102356191A (en) * 2009-03-18 2012-02-15 鲍姆胡特挤出有限责任公司 Polyethylene fiber, its use and process for its manufacture
US10000587B2 (en) 2012-08-31 2018-06-19 Baumhueter Extrusion Gmbh Cross-linked polyethylene fiber, its use and process for its manufacture

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PS Patent sealed
PCNP Patent ceased through non-payment of renewal fee