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WO1995026367A1 - Elastomeres a double reseau obtenus a partir de reseau d'elastomere oriente - Google Patents

Elastomeres a double reseau obtenus a partir de reseau d'elastomere oriente Download PDF

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Publication number
WO1995026367A1
WO1995026367A1 PCT/US1995/003875 US9503875W WO9526367A1 WO 1995026367 A1 WO1995026367 A1 WO 1995026367A1 US 9503875 W US9503875 W US 9503875W WO 9526367 A1 WO9526367 A1 WO 9526367A1
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WO
WIPO (PCT)
Prior art keywords
elastomeric
curing
cross
orientation
strain
Prior art date
Application number
PCT/US1995/003875
Other languages
English (en)
Inventor
Charles M. Roland
Patrick G. Santangelo
Original Assignee
The Government Of The United States Of America, Represented By The Secretary Of The Navy
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by The Government Of The United States Of America, Represented By The Secretary Of The Navy filed Critical The Government Of The United States Of America, Represented By The Secretary Of The Navy
Publication of WO1995026367A1 publication Critical patent/WO1995026367A1/fr

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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
    • C08J3/24—Crosslinking, e.g. vulcanising, of macromolecules
    • C08J3/244—Stepwise homogeneous crosslinking of one polymer with one crosslinking system, e.g. partial curing
    • 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
    • C08J2321/00—Characterised by the use of unspecified rubbers

Definitions

  • the present invention relates to the general area of modifying the structure of elastomers in order to obtain improved mechanical properties. More particularly, the present invention is directed to processes for modifying elastomeric structures to improve mechanical properties thereof, such as modulus, that involve subjecting elastomeric material to multiple curing steps that are controlled so as to introduce and apportion cross-links in each curing step to result in predetermined proportions of cross-link densities in the resultant elastomeric material as a result of the respective curing steps.
  • the present invention is directed to processes for modifying elastomeric materials that involve subjecting elastomeric material to an initial curing step under controlled conditions effective to result in a pre-cured elastomeric material comprising a first network having a number of cross-links within the range of about 5% to about 35% of the total cross-links of the resultant elastomeric material that has been subjected to another curing step while being subjected to an orientation strain under conditions effective to result in an elastomeric double network having desired total cross ⁇ links.
  • U.S. Patent No. 2,488,188, BALDWIN discloses that it is advantageous to first cure rubber slightly, then stretch it, followed by finish-curing the rubber while the rubber is in the stretched state to improve certain properties, e.g., tensile strength, elongation, elasticity, and elastic limit. It is disclosed that the invention applies to the curing of various types of natural rubber and unsaturated synthetic rubber polymers, such as chlorobutadiene polymers, copolymers of butadiene and acrylonitrile, copolymers of isobutylene with various diolefins, such as butadiene, isoprene, methyl butadiene, and the like.
  • Fig. 1 is graph showing the ratio of the double-to-single network moduli at various residual strains.
  • Fig. 2 is a graph showing the dependence of residual strain on stress strain isotherms.
  • Fig. 3 is a graph showing tensile strength measured for natural rubber double network samples of various residual strains.
  • Fig. 4 is a graph showing theoretical ratios of double-to- single network moduli at various residual strains using consecutive equations of Mooney and Rivlin.
  • the conditions of curing such as cure times and temperatures, are adjusted and controlled so that about 5% to about 35%, and more typically between about 5% to about 10%, of the total cross ⁇ links in the resultant double network elastomer are produced during the initial cure.
  • the pre-cured elastomer is stretched or strained during an orientation to at least 200% elongation, and more typically 600% elongation, and subjected to additional curing under conditions effective to produce a resultant elastomer double network having a desired cross-link density wherein between about 65% to about 95%, and more typically between about 90% to about 95%, of the total cross ⁇ links in the resultant elastomer double network are introduced during additional curing.
  • pre-cured sheets of a rubber such as natural rubber (NR) , polybutadiene (PBD) , and styrene-butadiene rubber (SBR)
  • NR natural rubber
  • PBD polybutadiene
  • SBR styrene-butadiene rubber
  • the final dimensions of the article reflect the relative cross-link densities arising from the two acts of curing, i.e., pre-curing and additional curing, along with the orientation during the second or additional cure.
  • the modulus of the double network elastomer produced in accordance with the present invention is higher than a conventional rubber or single network elastomer having the same total cross-link density.
  • the failure properties of the double network elastomer of the present invention are equivalent to the conventional rubber or single network elastomer when no crystallization takes place.
  • the resistance to failure of the double network elastomer of the present invention is better than that of the conventional rubber or single network elastomer having the same total cross-link density.
  • the present invention enables higher modulus to be realized while simultaneously maintaining or improving failure performance.
  • (iii) maintains or improves failure properties of elastomers.
  • rubber is cured while unrelaxed, e.g., while stretched, such that the subsequent state of elastic equilibrium is shifted away from zero strain.
  • the resultant double network elastomer structure provides thermodynamically stable orientation, which significantly alters the mechanical properties of an elastomer.
  • the failure properties are maintained by keeping a constant cross-link density, while the modulus is enhanced by double network formation.
  • an enhancement of strain crystallizability can be obtained by virtue of the double network process. This leads to significantly better failure properties, since the strain crystallization is the primary mechanism for failure resistance.
  • the process of the present invention involves the following steps: a) curing elastomeric material under conditions of substantially zero strain, time and temperature to result in a pre-cured elastomeric network comprising less than about 40%, and more typically less than about 35%, of total cross-links that are present in the resultant elastomeric double network structure; b) subjecting the pre-cured elastomeric material to an orientation technique to result in an oriented elastomeric material having at least about 200% elongation; and c) curing the oriented elastomeric material while maintaining such orientation under conditions effective to result in a resultant elastomeric structure comprising a predetermined cross-link density of at least about 60%, and more typically at least about 65%, of total cross-links present in the resultant elastomeric double network structure, wherein the resultant elastomeric double network structure exhibits enhanced modulus.
  • the cure times and temperatures are adjusted and controlled so that most typically between about 5% to about 35%, and most often between about 5% to about 10%, of the total cross-links of the resultant elastomeric double network structure are produced during initial cure at zero strain.
  • the pre-cured elastomer is stretched during an orientation to at least about 200% elongation, and more typically 600% elongation, and cured to produce a resultant elastomer double network having between about 65% to about 95% and more typically between about 90% to about 95% of the total cross-links.
  • conditions during the curing steps are effective to result in magnitude of orientation sufficient to result in enhanced modulus.
  • suitable methods of cross-linking include essentially all conventional curing methods, i.e., sulfur vulcanization, efficient vulcanization
  • elastomers include: for neoprenes, metal oxides; phenolformaldehyde resins for butyl rubber; and for butyl and other unsaturated rubbers, p-benzoquinone dioxime.
  • achieving a desired proportioning of the total cross-link density is accomplished in different manners depending on the particular method of cross-linking.
  • time and temperature are the primary variables used to control the cross-link apportionment. Radiation curing would rely on dose,
  • curing systems i.e., radiation intensity and exposure time.
  • curing systems selected from the group consisting of sulfur vulcanization, peroxide curing, and radiative curing.
  • Sulfur vulcanization typically has two stages.
  • the first stage referred to as the induction or scorch period, involves the curing agents reacting with themselves prior to actual cross-linking reaction.
  • the time of the second stage, where cross-links are actually formed is important.
  • the length of time for each stage of the process is dependent on the temperature and the amount and type of curatives used.
  • the scorch period at a given cure temperature, it is possible for the first cross-link density of a soluble network rubber to have a smaller percentage of the total cross-links even while experiencing a longer cure time than the second cross-linking period.
  • Peroxide curing involves the formation of thermal decomposition of an organic peroxide. These react with the elastomer to produce polymer radicals which combine to form a cross-link. Therefore, the rate of cross-linking is dependent on the rates of peroxide decomposition and polymer radical production.
  • Radiative puring typically also proceeds via radical mechanisms.
  • the polymer radicals produced through the use of energizing radiation combine to produce a cross-link.
  • the number of cross-links produced by this technique is a function of the duration and intensity of radiation used.
  • orientation is accomplished using orientation techniques.
  • typical orientation techniques include those selected from the group of orientation procedures comprising uniaxial extension, biaxial extension, simple shear, planar shear, and inflation.
  • the strains at which the second cross-linking is to be introduced into the elastomeric double network is specified to be in the range from 20% to 600% elongation. Below 20% elongation, there are no beneficial effects on properties as compared to conventional rubbers. More typically, however, the lower limit of elongation is about 200% elongation.
  • the upper limit for the cross-linking strain is in principle the material's maximum extensibility; however, in practice this yields an overly large "rejection rate", that is, many samples fail during their production. For practical reasons, therefore, the strain during cross-linking is more typically limited to not greater than 600%.
  • the number of cross-links generated in the first network is specified to be in the range from about 5% to about 35% of the total cross-links introduced into the resultant double network material. If less than 5% of the total cross-links ultimately present in the final resultant double network are introduced during the initial stage of cross-linking in forming the first network, then the material will not have the coherent strength to survive the second stage of the cross-linking process. No beneficial effects are realized in double network material if the number of cross-links introduced into the first network exceeds about 35 % of the total number of cross-links in the resultant double network elastomer.
  • conventional procedures for the measurement of cross-link density are used.
  • conventional cross-link measurement procedures include (i) determination of the degree of swelling in a solvent, and (ii) determining the equilibrium (fully-relaxed) modulus.
  • suitable elastomeric material includes members selected from the group consisting of elastomers not capable of strain induced crystallization, and elastomers capable of strain-induced crystallization, wherein elastomeric materials not capable of strain-induced crystallization comprise at least one member selected from the group consisting of unsaturated synthetic rubber polymers, copolymers of butadiene and styrene, copolymers of butadiene and acrylonitrile, and elastomers capable of strain induced crystallization include members selected from the group consisting of natural rubber (NR) polybutadiene (PBD) , styrene butadiene (SBR), polyisobutylene (PIB), and high cis 1,4 - polybutadiene (high cis 1,4 - PBR) .
  • NR natural rubber
  • PBD polybutadiene
  • SBR styrene butadiene
  • PIB polyisobutylene
  • the conditions during curing are sufficient to maintain a constant cross link density in said double network elastomer while the modulus is enhanced, and while at least failure performance of the elastomeric structure is maintained.
  • a rubber incapable of strain crystallizing by virtue of its chemical structure, such as SBR, nitrile rubber, and the like, compared in a fully relaxing deformation cycle to a non-relaxing deformation cycle.
  • a rubber capable of strain crystallization e.g., natural rubber, neoprene, and the like, will have a markedly longer fatigue life for non-relaxing deformations as compared to fully relaxing deformations.
  • the present invention in part, is based on the discovery that one can take advantage of double network elastomers and attain non-relaxing deformation levels of performance even when they are subjected to fully relaxing deformation cycles. This is a result of the intrinsic orientation of the double network rubber. Accordingly, elastomeric or rubber parts and devices may be designed and developed without the constraint of having to avoid fully relaxing deformations. Furthermore, applications for which fully relaxing conditions are unavoidable can obviously benefit from the use of double network technology in accordance with the present invention.
  • Example I The following example was conducted to demonstrate aspects of the present invention.
  • Fig. 1 the ratio of double-to single-network moduli has been plotted at various residual strains. The data is taken from Fig. 2 at an extension ratio of 1.1. In Fig. 2, dependence of residual strain on stress-strain isotherms is
  • the double-network rubbers and the single- network rubber i.e., residual strain of 1.0 have the same total cross-link density.
  • Fig. 3 the tensile strength measured for natural rubber double-networks samples of various residual strains has been plotted on the graph. Also shown is the tensile strength of a single-network rubber (residual strain of 1.0) having the same total cross-link density.
  • the double-networks posses an elevated modulus while maintaining strength.
  • Second Cure 90 minutes at 160°C while strained to indicated level.
  • Example II The following example was conducted to demonstrate aspects of the present invention. In this Example II, unlike Example I, the cure distribution was not weighted towards the second network.
  • Example III The following example was conducted to demonstrate aspects of the present invention using a: Sulfurless Cure System. Natural Rubber 100 parts N2 34 Black 55 parts
  • First Cure 15 minutes at 145°C
  • Second Cure Stretch to 400% the 32 minutes at 145 ⁇ C

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  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Organic Chemistry (AREA)
  • Tires In General (AREA)
  • Compositions Of Macromolecular Compounds (AREA)

Abstract

Un procédé permettant de modifier des structures élastomères et d'améliorer des propriétés mécaniques comprend plusieurs étapes. On applique tout d'abord une technique d'orientation à un matériau élastomère précuit afin d'obtenir un matériau élastomère orienté; on cuit ensuite ce matériau élastomère orienté tout en maintenant son orientation dans des conditions permettant d'obtenir une structure élastomère présentant une densité de réticulation prédéterminée et un module amélioré, l'orientation étant suffisamment importante pour entraîner une amélioration du module. Généralement, les techniques d'orientation utilisées peuvent être les suivantes: étirage uniaxial, étirage biaxial, cisaillement simple, cisaillement planaire et gonflement. Le matériau élastomère est capable ou non de cristallisation induite par déformation. On obtient l'amélioration du module en maintenant au moins les propriétés de rupture de la structure élastomère. Les conditions pendant la cuisson suffisent à maintenir une densité de réticulation constante dans l'élastomère à double réseau et à améliorer le module.
PCT/US1995/003875 1994-03-29 1995-03-29 Elastomeres a double reseau obtenus a partir de reseau d'elastomere oriente WO1995026367A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US21931894A 1994-03-29 1994-03-29
US08/219,318 1994-03-29

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WO1995026367A1 true WO1995026367A1 (fr) 1995-10-05

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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8227551B2 (en) 2008-11-10 2012-07-24 The University Of Massachusetts Polymeric compositions, methods of manufacture thereof and articles comprising the same
US10336018B2 (en) * 2016-09-28 2019-07-02 Acushnet Company Method of making a golf ball incorporating at least one elongated thermoset layer
US10465070B2 (en) * 2016-09-28 2019-11-05 Acushnet Company Golf balls incorporating double network cross-linked compositions comprising a base thermoset composition
US10465072B2 (en) * 2016-09-28 2019-11-05 Acushnet Company Golf balls incorporating double network cross-linked compositions comprising a base thermoplastic

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2488112A (en) * 1945-12-29 1949-11-15 Standard Oil Dev Co Process of curing isobutyleneisoprene copolymers
US3684782A (en) * 1967-09-12 1972-08-15 Paolo Longi Manufactured shaped articles of unsaturated olefinic copolymers
US4740335A (en) * 1985-08-10 1988-04-26 Firma Carl Freudenberg Process for producing a deep-drawn article from a partially-crystalline polymeric material

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2488112A (en) * 1945-12-29 1949-11-15 Standard Oil Dev Co Process of curing isobutyleneisoprene copolymers
US3684782A (en) * 1967-09-12 1972-08-15 Paolo Longi Manufactured shaped articles of unsaturated olefinic copolymers
US4740335A (en) * 1985-08-10 1988-04-26 Firma Carl Freudenberg Process for producing a deep-drawn article from a partially-crystalline polymeric material

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8227551B2 (en) 2008-11-10 2012-07-24 The University Of Massachusetts Polymeric compositions, methods of manufacture thereof and articles comprising the same
US10336018B2 (en) * 2016-09-28 2019-07-02 Acushnet Company Method of making a golf ball incorporating at least one elongated thermoset layer
US10465070B2 (en) * 2016-09-28 2019-11-05 Acushnet Company Golf balls incorporating double network cross-linked compositions comprising a base thermoset composition
US10465072B2 (en) * 2016-09-28 2019-11-05 Acushnet Company Golf balls incorporating double network cross-linked compositions comprising a base thermoplastic

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