Synthetic Polyisoprene Latex Condoms With Two-Stage Vulcanization
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Solution Overview
Problem
Existing methods for producing synthetic polyisoprene condoms result in the formation of cancer-causing nitrosamines during the vulcanization process, which are harmful to workers and users, and do not provide adequate strength and stretchability.
Innovation Solution
A method involving the use of multiple accelerators that activate at different temperatures to pre-vulcanize polyisoprene latex, forming bonds without overcuring, and using a surfactant-stabilized latex emulsion to prevent agglomeration, ensuring intra- and inter-particle crosslinking at reduced temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional vulcanization process is used to produce synthetic polyisoprene condoms, then the condoms achieve adequate strength and cross-linking, but nitrosamines are formed during the process which are harmful to workers and users
Solution Approach 1:
The patent changes the vulcanization parameters by using a two-stage process: first stage at 40-60°C for pre-vulcanization with dithiocarbamate accelerator, and second stage at 90-120°C for completion with thiuram accelerator. This temperature parameter change prevents nitrosamine formation while achieving adequate cross-linking and strength.
Solution Approach 2:
The patent segments the vulcanization process into two distinct stages with different temperature ranges and accelerator systems. The first stage uses dithiocarbamate at lower temperature (40-60°C) to initiate cross-linking without forming nitrosamines, and the second stage uses thiuram at higher temperature (90-120°C) to complete the vulcanization, thereby resolving the contradiction between strength development and nitrosamine prevention.
2Object-affected harmful factors
If reduced temperature vulcanization is used to eliminate nitrosamine formation, then worker and user safety is improved, but the condom may not achieve adequate strength and stretchability
Solution Approach 1:
The patent divides the vulcanization process into two temperature stages: 40-60°C for pre-vulcanization and 90-120°C for completion. This segmentation allows the first stage to occur at nitrosamine-free temperatures while the second stage provides the thermal energy needed for adequate cross-linking and mechanical property development.
Solution Approach 2:
The patent performs preliminary vulcanization at 40-60°C using dithiocarbamate accelerator before the final high-temperature stage. This preliminary action initiates cross-linking at safe temperatures, and the subsequent 90-120°C stage completes the vulcanization to achieve the required strength, stretchability, and durability without nitrosamine formation.
3Object-affected harmful factors
If multiple accelerators are used to enable low-temperature vulcanization, then the process complexity increases, but nitrosamine formation is prevented
Solution Approach 1:
The patent segments the accelerator system into two functional components: dithiocarbamate for low-temperature activation (40-60°C) and thiuram for high-temperature completion (90-120°C). This segmentation enables each accelerator to operate in its optimal temperature range, preventing nitrosamine formation while achieving complete vulcanization.
Solution Approach 2:
The patent changes the accelerator activation parameters by selecting accelerators with different temperature thresholds. Dithiocarbamate activates at 40-60°C without forming nitrosamines, while thiuram activates at 90-120°C to complete the process. This parameter change in accelerator selection and activation temperature prevents nitrosamine formation despite using multiple accelerators.
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 process produces highly stretchable and tear-resistant condoms with minimal nitrosamine content, maintaining physical integrity and safety for workers and users.
Implementation Method 1
The effectiveness of sulfur crosslinking agent is improved by conventional accelerators including dithiocarbamate, thiazoles, guanidines, thioureas, amines, disulfides, thiurams, xanthates and sulfonamides
Implementation Method 2
to complete the cross-linking of the rubber film
Implementation Method 3
using a surfactant-stabilized latex emulsion to prevent agglomeration
Implementation Method 4
dip formed using the pre-vulcanized aqueous latex emulsion and vulcanized for a short time at a reduced temperature of only 90° C. to 120° C.
Data Source
AI summary
A synthetic polyisoprene latex emulsion has pre-vulcanization composition and post vulcanization composition. The pre-vulcanization composition comprises insoluble amorphous sulfur extracted with zinc dithiocarbamate catalyst at 20° C. to form sulfur chain and transported to interior of synthetic polyisoprene particle forming physical attachment of sulfur to active sites. The degree of pre-vulcanization is verified by expansion of cast and dried film of latex in toluene in 20 minutes by means of a swelling index test. The latex emulsion is vulcanized at 90° C. to 120° C. for 3 to 5 minutes. Post-vulcanization composition with accelerators crosslink between synthetic polyisoprene particles, uniformly curing both in the inter-particle and intra-particle regions to produce high cross link density, uniform distribution of double bonds with zinc segregation at the boundaries of original particles. The condom exhibits high tensile strength, tensile modulus, elongation with excellent tear strength releasing below 10 ppb of nitrosamines.