Dip-formed synthetic polyisoprene latex articles with improved intraparticle and interparticle crosslinks
A synthetic polyisoprene latex emulsion has pre-vulcanization composition and post vulcanization composition. The pre-vulcanization composition comprises soluble sulfur with high S 8 ring structure that is catalytically broken by a zinc dithiocarbamate. Surfactants present in the pre-vulcanization composition wets synthetic polyisoprene particles and permeates small sized sulfur and accelerator molecules into the interior of these particles thereby pre-vulcanizing the particles. The degree of pre-vulcanization is verified by isopropanol index test. The latex emulsion has post-vulcanization composition with accelerators that crosslink inter-particle region during post vulcanization cure cycle. The dipped synthetic polyisoprene article is substantially uniformly cured both in the inter-particle and intra-particle regions and reliably exhibits high cross link density, uniform distribution of double bonds in TEM and zinc segregation at the boundaries or original particles by electron microprobe analysis. The films exhibit high tensile strength, tensile modulus, tear strength, burst pressure and burst volume.
1. A synthetic polyisoprene elastomeric glove or condom made of a layer of elastomer comprising:
synthetic polyisoprene particles;
inter-polyisoprene particle crosslinks; and
intra-polyisoprene particle crosslinks,
wherein the intra-polyisoprene particle crosslinks and inter-polyisoprene particle crosslinks are substantially uniformly distributed among and between the synthetic polyisoprene particles.
2. The glove or condom of claim 1 , wherein such uniformity is measured by one or more of the following
(a) the glove or condom exhibits a substantially conchoidal fracture when fractured at liquid nitrogen temperature, or
(b) the glove or condom exhibits a fracture surface with an absence of scanning electron microscope-viewable intra-polyisoprene particle and inter-polyisoprene particle features when ruptured at room temperature, or
(c) osmium tetroxide staining.
3. A condom of claim 2 , wherein the glove or condom is formed of two or more thin layers of said elastomer consistent with dipping on a former without coagulant on the former.
4. The glove or condom of claim 2 , wherein the synthetic polyisoprene particles range in size from about 0.2 to about 2.0 micron.
5. A condom of claim 1 , wherein the condom has a tensile strength of at least 30 MPa.
6. The condom of claim 5 , wherein the condom exhibits a fracture surface with an absence of scanning electron microscope-viewable intra-polyisoprene particle and inter-polyisoprene particle features when ruptured at room temperature.
7. The condom of claim 1 , wherein the condom is formed of two or more thin layers of said elastomer consistent with dipping on a former without coagulant on the former.
8. The glove or condom of claim 1 , wherein said glove or condom exhibits a substantially conchoidal fracture when fractured at liquid nitrogen temperature.
9. The glove or condom of claim 1 , wherein the synthetic polyisoprene particles range in size from about 0.2 to about 2.0 microns.
10. The glove or condom of claim 9 , wherein the glove or condom exhibits a fracture surface with an absence of scanning electron microscope-viewable intra-polyisoprene particle and inter-polyisoprene particle features when ruptured at room temperature.
11. The glove or condom of claim 1 , wherein the glove or condom exhibits a fracture surface with an absence of scanning electron microscope-viewable intra-polyisoprene particle and inter-polyisoprene particle features when ruptured at room temperature.
12. A condom of claim 11 , wherein the condom has an elongation at break of at least 945%.
13. A condom of claim 12 , wherein said glove or condom exhibits a substantially conchoidal fracture when fractured at liquid nitrogen temperature.
14. The glove or condom of claim 1 , wherein the glove or condom exhibits scanning electron microscopic-viewable zinc and sulfur x-ray maps on a fracture surface when fractured at liquid nitrogen temperature, or when ruptured at room temperature, or both, shows presence of sulfur within a polyisoprene particle that is decorated by zinc.
15. The glove or condom of claim 1 , wherein the glove or condom, exhibits, by microprobe elemental analysis, an accumulation of zinc surrounding said synthetic polyisoprene particles.
16. The glove or condom of claim 1 , wherein TEM of an osmium tetroxide treated said glove or condom shows uniformity of isoprene double bonds.
17. The glove or condom of claim 1 , wherein the glove or condom exhibits uniform intra-polyisoprene particle crosslinks and inter-polyisoprene particle crosslinks when fractured is such that a fracture surface passes through both inter-particle regions and intra-particle regions nonpreferentially.
18. A condom of claim 17 , having an elongation at break of at least 945%.
19. The condom of claim 18 , having a tensile strength of at least 30 MPa.
20. A condom of claim 1 , having an elongation at break of at least 945%.