The Hidden Truth Behind PVC Cable Material in the Cable Industry

The Hidden Truth Behind PVC Cable Material in the Cable Industry

I. Flame-Retardant PVC Cable Materials

Polyvinyl chloride (PVC) resin, a time-tested thermoplastic, can have its flexibility adjusted by adding varying amounts of plasticizers. It can also be blended with other polymers to produce plastic products with diverse properties. PVC is cost-effective and has excellent performance, making it widely used in the wire and cable industry. For instance, PVC is commonly used as the base resin for insulated wires and cables with voltages of 450V/750V or below, as well as flexible cables. With the widespread application of flame-retardant PVC cable materials in electronics, computers, automobiles, and aerospace industries, the demand for flame-retardant properties in cables is increasing. PVC cables, due to the addition of large amounts of plasticizers and other additives, have insufficient flame resistance. During combustion, they produce harmful HCl gas, which is also highly corrosive to metals. In addition to producing toxic gases, incomplete combustion of certain gases can generate large amounts of smoke, severely endangering public safety and property. Therefore, the research and development of low-smoke, low-toxicity PVC cables have become an urgent need in the cable flame-retardant industry, holding significant social value.

II. Flame-Retardant and Smoke-Suppression Methods

In PVC cables, we typically achieve flame-retardant and smoke-suppressing effects by adding flame-retardant agents and flame-retardant plasticizers. The specific methods are as follows:

1. Replacing conventional plasticizers with flame-retardant plasticizers. For example, triaryl phosphate esters and alkyl diaryl phosphate esters are commonly used as plasticizers. When burned, they thermally decompose to form non-volatile polyphosphates, which can form a protective layer on the solid surface to block contact with oxygen. Chlorinated paraffin can also be added as a synergistic plasticizer to enhance flame-retardant performance.

2. Adding inorganic flame retardants such as antimony compounds and metal hydroxides. The aluminum hydroxide typically added also has a significant smoke-suppressing effect.

3. When the plasticizer content is high, use a method that simultaneously adds flame-retardant plasticizers, inorganic flame retardants, and flame-retardant fillers.

4. Smoke suppressants are also commonly added. The main smoke suppressants used in PVC cable compounds include molybdenum trioxide and ammonium octamolybdate. In the formulation of PVC cable compounds, we often need to select the appropriate ratio of flame-retardant plasticizers to conventional plasticizers based on the specific application and flame-retardant requirements of the cable compound, thereby achieving a high cost-effectiveness ratio.

III. Research Progress on Flame-Retardant Performance

In addition to meeting the general performance standards for PVC cable materials in terms of electrical and physical-mechanical properties, PVC cable materials must also have excellent flame-retardant performance. Flame-retardant performance is typically measured by the oxygen index, which refers to the minimum oxygen concentration required to sustain combustion of a sample. A higher oxygen index indicates better flame-retardant performance. Materials with an oxygen index above 30 are generally considered to have adequate flame-retardant properties. The following primarily introduces the factors influencing the flame-retardant performance of PVC cable compounds and the domestic and international research progress in enhancing their flame-retardant performance.

IV. Influence of Plasticizer Content on Flame-Retardant Performance

Different plasticizers added to PVC cable compounds will result in varying flame-retardant and smoke-generating properties of the cable compounds. Among the four most commonly used plasticizers in PVC cable compounds—dioctyl phthalate, trioctyl trimellitate, triphenyl phosphate, and polyester-based plasticizers—their flame-retardant properties vary significantly. Scientists have conducted relevant research on this topic. When 30–60 parts of plasticizer were added to 100 parts of soft PVC, it was found that as the plasticizer content increased, the oxygen index of PVC decreased. For different plasticizers, the rate of decrease was generally consistent. PVC containing triphenyl phosphate had the highest oxygen index, which was approximately 5 points higher than that of PVC containing dioctyl phthalate. Studies on smoke generation indicate that PVC containing dioctyl phthalate and triphenyl phosphate exhibits increased smoke generation as the plasticizer content increases. However, PVC containing trioctyl trimellitate and polyester-based plasticizers shows the opposite result.

V. Effect of Flame-Retardant Dosage on Flame-Retardant Performance

Inorganic flame retardants such as Al(OH)₃, Sb₂O₃, and zinc borate (ZB) are added to PVC cable compounds, and their dosage significantly affects the flame-retardant performance of PVC. Domestic and international scholars have conducted extensive research on this topic. Some scholars studied the effect of Sb₂O₃ and Sb₂O₃/ZB composite flame retardant dosage on the oxygen index of PVC. They found that as the amount of Sb₂O₃ increased, the limiting oxygen index of PVC cable compounds showed a linear upward trend. When the addition of nano-Sb₂O₃ exceeded 1.5 parts, the contribution of nano-Sb₂O₃ to the oxygen index of PVC was greater than that of micron-sized Sb₂O₃. They also studied the oxygen index of PVC at different mass ratios of Sb₂O₃ to ZB, finding that the oxygen index decreased as the mass ratio increased. This means that the more Sb₂O₃ added, the higher the flame-retardant performance of PVC. However, since Sb₂O₃ is relatively expensive, the amount added is generally not very high, as long as it ensures adequate flame-retardant properties. Additionally, the added ZB can serve as a smoke suppressant. Combining ZB with Sb₂O₃ enables PVC cable compounds to achieve both an appropriate oxygen index and low smoke generation.

VI. Effect of Filler Quantity on Flame-Retardant Performance

In PVC cable compounds, a certain amount of filler is typically added. When talc and kaolin are used as fillers, the oxygen index increases by 1 to 2 times, but the burning rate of the cable compound also doubles, while the maximum extinction coefficient remains unchanged. When Al(OH)₃ is used as a filler, the burning rate increases by 50%, the oxygen index increases, and the maximum extinction coefficient decreases, so it has a better effect in suppressing smoke generation. CaCO₃ fillers are also commonly added to PVC. Scientists have found that as the amount of CaCO₃ added increases, the oxygen index of PVC cable compounds decreases, and the maximum extinction coefficient also decreases. Therefore, the amount of CaCO₃ added should not be excessive, as this would impair the flame-retardant and smoke-suppression performance of the cable compound. However, CaCO₃ can serve as an effective capture agent for HCl gas, demonstrating highly significant efficacy.

Among the various innovative solutions for enhancing the flame-retardant performance of PVC cables, one standout option is the application of specialized flame-retardant additives developed by Guangzhou Yinsu Flame Retardant. The company has made significant advancements in creating non-halogen flame retardants, micro-encapsulated red phosphorus flame retardants, and eco-friendly synergists. Their flagship micro-encapsulated red phosphorus flame retardant, FRP-950X, is a low-smoke, low-toxicity additive that offers superior flame retardancy without releasing harmful halogens during combustion, making it ideal for high-performance PVC cable formulations. T3 is a antimony trioxide replacement, provides comparable flame retardant performance to traditional antimony compounds but eliminates the health and environmental risks often associated with them.Can effectively enhances the flame retardancy of PVC compounds while maintaining mechanical properties. By integrating these advanced flame-retardant solutions into PVC cable designs, manufacturers can significantly improve safety while meeting the ever-evolving regulatory and market demands for low-smoke, low-toxicity cable materials.