Synthetic Polyisoprene Latex Intraparticle Crosslinking
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Solution Overview
Problem
Synthetic polyisoprene latex films have inferior properties compared to natural rubber due to lower stereo-regularity and molecular weight, leading to nonhomogeneous cure properties, poor strength, and elongation, with a tendency to flock and form defects in dipped articles, and existing methods require coagulants that hinder the production of thin, continuous layers.
Innovation Solution
A pre-vulcanized synthetic latex emulsion with soluble sulfur and zinc dithiocarbamate is used to permeate sulfur into synthetic polyisoprene particles, combined with post-vulcanization accelerators to achieve intra-particle and inter-particle crosslinking, allowing for coagulant-free dip-forming of articles with improved strength and stretchability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If synthetic polyisoprene latex is used to replace natural rubber, then protein allergy is eliminated, but the film properties (strength and elongation) become inferior
Solution Approach 1:
The patent changes the chemical parameters of synthetic polyisoprene by incorporating specific additives (sulfur, zinc oxide, accelerators) and controlling polymerization conditions to achieve higher cis-1,4 content and appropriate molecular weight, thereby improving film properties while maintaining the allergy-free advantage
Solution Approach 2:
The patent creates a composite system by combining synthetic polyisoprene with cross-linking agents and additives to form a vulcanized network structure, which enhances mechanical properties while preserving the hypoallergenic characteristic
2Stability of the object's composition
If conventional cross-linking agents are added to synthetic polyisoprene latex, then inter-particle cross-links increase, but intra-particle cross-links decrease, leading to nonhomogeneous cure properties
Solution Approach 1:
The patent applies different cross-linking mechanisms to different regions: intra-particle cross-linking through sulfur diffusion into particles, and inter-particle cross-linking through the continuous phase, creating locally optimized cross-link density that ensures homogeneous overall cure
Solution Approach 2:
The patent uses zinc oxide and accelerators as intermediary substances that facilitate uniform sulfur distribution and promote simultaneous intra- and inter-particle cross-linking, achieving homogeneous cure properties
3Duration of action of stationary object
If synthetic polyisoprene latex is used without pre-vulcanization, then the latex remains stable for dipping, but the resulting film has poor strength and elongation properties
Solution Approach 1:
The patent performs preliminary vulcanization by incorporating sulfur and accelerators into the latex formulation before dipping, allowing cross-linking to begin during the dipping process while maintaining latex stability, thereby achieving both processability and improved mechanical properties
4Quantity of substance
If synthetic polyisoprene latex has low stereo-regularity, then production cost is reduced, but the film properties become inferior compared to natural rubber
Solution Approach 1:
The patent optimizes polymerization parameters including catalyst selection, temperature control, and monomer purity to achieve high cis-1,4 content in synthetic polyisoprene, thereby improving film properties to match natural rubber while maintaining cost-effectiveness through efficient production processes
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method results in synthetic polyisoprene films with high tensile strength, elongation, and uniform crosslink density, producing defect-free, continuous layers with enhanced mechanical properties and stability, comparable to natural rubber.
Implementation Method 1
soluble sulfur and zinc dithiocarbamate is used to permeate sulfur into synthetic polyisoprene particles
Implementation Method 2
pre-vulcanized synthetic latex emulsion with soluble sulfur and zinc dithiocarbamate
Implementation Method 3
dip formed into a thin latex article from an aqueous latex emulsion
Implementation Method 4
achieve intra-particle and inter-particle crosslinking
Data Source
AI summary
A synthetic polyisoprene latex emulsion has pre-vulcanization composition and post vulcanization composition. The pre-vulcanization composition comprises soluble sulfur with high S8 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.