PVC stabilizers are additives used to improve the thermal stability of polyvinyl chloride (PVC) and its copolymers. For PVC plastics, if the processing temperature exceeds 160℃, thermal decomposition will occur and HCl gas will be produced. If not suppressed, this thermal decomposition will be further aggravated, influencing the development and application of PVC plastics.
Studies found that if PVC plastics contain tiny amounts of lead salt, metal soap, phenol, aromatic amine, and other impurities, its processing and application won’t be affected, however, its thermal decomposition can be mitigated to a certain extent. These studies promote the establishment and continuous development of PVC stabilizers.
Common PVC stabilizers include organotin stabilizers, metal salt stabilizers, and inorganic salt stabilizers. Organotin stabilizers are widely used in the production of PVC products because of their transparency, good weather resistance, and compatibility. Metal salt stabilizers usually use calcium, zinc, or barium salts, which can provide better thermal stability. Inorganic salt stabilizers such as tribasic lead sulfate, dibasic lead phosphite, etc. have long-term thermostability and good electrical insulation. When choosing a suitable PVC stabilizer, you need to consider the application conditions of PVC products and the required stability properties. Different stabilizers will affect the performance of PVC products physically and chemically, so strict formulation and testing are required to ensure the suitability of stabilizers. The detailed introduction and comparison of various PVC stabilizers are as follows:
Organotin Stabilizer: Organotin stabilizers are the most effective stabilizers for PVC products. Their compounds are the reaction products of organotin oxides or organotin chlorides with appropriate acids or esters.
Organotin stabilizers are divided into sulfur-containing and sulfur-free. Sulfur-containing stabilizers’ stability is outstanding, but there are problems in taste and cross-staining similar to other sulfur-containing compounds. Non-sulfur organotin stabilizers are usually based on maleic acid or half maleic acid esters. They like methyl tin stabilizers are less effective heat stabilizers with better light stability.
Organotin stabilizers are mainly applied to food packaging and other transparent PVC products like transparent hoses.
Lead Stabilizers: Typical lead stabilizers include the following compounds: dibasic lead stearate, hydrated tribasic lead sulfate, dibasic lead phthalate, and dibasic lead phosphate.
As heat stabilizers, lead compounds won’t damage the excellent electrical properties, low water absorption, and outdoor weather resistance of PVC materials. However, lead stabilizers have disadvantages such as:
- Having toxicity;
- Cross-contamination, especially with sulfur;
- Generating lead chloride, which will form streaks on the finished products;
- Heavy ratio, resulting in unsatisfactory weight/volume ratio.
- Lead stabilizers often make PVC products opaque immediately and discolor quickly after sustained heat.
In spite of these disadvantages, lead stabilizers are still widely adopted. For electrical insulation, lead stabilizers are preferred. Benefiting from its general effect, many flexible and rigid PVC products are realized such as cable outer layers, opaque PVC hard boards, hard pipes, artificial leathers, and injectors.
Metal salt stabilizers: Mixed metal salt stabilizers are aggregates of various compounds, usually designed according to specific PVC applications and users. This kind of stabilizer has evolved from the addition of barium succinate and cadmium palm acid alone to the physical mixing of barium soap, cadmium soap, zinc soap, and organic phosphite, with antioxidants, solvents, extenders, plasticizers, colorants, UV absorbers, brighteners, viscosity control agents, lubricants, and artificial flavors. As a result, there are many factors that can affect the effect of the final stabilizer.
Metal stabilizers, such as barium, calcium, and magnesium do not protect the early color of PVC materials but can provide long-term heat resistance. PVC material stabilized in this way starts out yellow/orange, then gradually turns to brown, and finally to black after constant heat.
Cadmium and zinc stabilizers were first used because they are transparent and can maintain the original color of PVC products. The long-term thermostability provided by cadmium and zinc stabilizers is much worse than that offered by barium ones, which tend to suddenly degrade completely with little or no sign.
In addition to the factor of metal ratio, the effect of metal salt stabilizers is also related to their salt compounds, which are the main factors affecting the following properties: lubricity, mobility, transparency, pigment color change, and thermal stability of PVC. Below are several common mixed metal stabilizers: 2-ethylcaproate, phenolate, benzoate, and stearate.
Metal salt stabilizers are widely used in soft PVC products and transparent soft PVC products like food packaging, medical consumables, and pharmaceutical packaging.
Post time: Oct-11-2023