Among rubber hose products, the low-temperature brittle temperature (T/T) of high-pressure hose is a key indicator of its reliability in cold environments. The vulcanization system, as a key factor influencing the rubber's molecular structure, plays a decisive role in the low-temperature performance of high-pressure hose. By adjusting the crosslinking bond type and the ratio of vulcanizer to accelerator in the vulcanization system, molecular chain flexibility can be significantly optimized, thereby lowering the T/T and improving the hose's adaptability to low-temperature environments.
In traditional vulcanization systems, high sulfur content in high-pressure hoses can easily form polysulfide bonds, accompanied by intramolecular crosslinking and cyclization reactions. This structure restricts molecular chain mobility, leading to an increase in the glass transition temperature (T/T), and consequently, an increase in the T/T. For example, when natural rubber is vulcanized using traditional vulcanization systems, increasing the sulfur content increases the shear modulus and the T/T can rise by 20-30°C, directly weakening the high-pressure hose's elasticity and impact resistance at low temperatures.
The semi-effective vulcanization system achieves a balanced ratio of polysulfide bonds to disulfide bonds by reducing sulfur usage (0.8-1.5 parts) and optimizing the accelerator ratio. This system reduces the likelihood of intramolecular sulfur incorporation, reduces resistance to chain mobility, and minimizes the rise in the glass transition temperature of high-pressure hoses. For example, in cold-resistant high-pressure hose formulations, the use of a semi-effective vulcanization system can reduce the brittle temperature by 5-10°C compared to conventional systems, significantly improving sealing performance and fatigue resistance in low-temperature environments.
The effective vulcanization system further reduces sulfur usage (0.3-0.5 parts) and increases the high accelerator content (2-4 parts), primarily forming monosulfide and disulfide bonds. This structure imparts superior heat and aging resistance to high-pressure hoses while also lowering the brittle temperature by reducing polysulfide bond distortion and hysteresis losses. For example, in high-pressure fuel hoses, the use of an effective vulcanization system can reduce the brittle temperature by over 7°C compared to conventional systems, meeting the requirements for use in extremely cold regions.
Peroxide cure systems provide high-pressure hoses with a more stable molecular structure by forming C-C crosslinks. Compared to sulfur cure, peroxide-cured rubber has a larger coefficient of volume expansion, providing more free space for chain segment movement and thus lowering the glass transition temperature. For example, in high-pressure hydraulic hoses, using DCP peroxide cure can lower the brittle temperature by 10–15°C compared to sulfur cure systems, while also improving oil resistance and compression set resistance.
The synergistic effect of plasticizers and cure systems is crucial for the low-temperature performance of high-pressure hoses. Polar rubbers (such as nitrile rubber and chloroprene rubber) require plasticizers with matching polarity (such as dioctyl adipate and dioctyl sebacate) to increase molecular chain flexibility and lower the glass transition temperature. For example, in high-pressure oil-resistant hoses, adding 10–15 phr of DOA plasticizer can lower the brittle temperature by 5–8°C while maintaining excellent oil resistance and sealing properties.
In practical applications, adjustments to the vulcanization system for high-pressure hoses must balance low-temperature performance with other physical properties. For example, in aviation hydraulic hoses, optimizing the vulcanization system and plasticizer ratio can reduce the brittle temperature to below -55°C while meeting high-pressure resistance, fuel resistance, and aging resistance requirements. Furthermore, combining low-temperature flattening tests with temperature retraction tests (TR10) can accurately assess the impact of vulcanization system adjustments on the low-temperature performance of high-pressure hoses, providing data support for formulation optimization.
