Introduction to commonly used inorganic fillers for plastics
Glass Fiber
Glass fiber is a filler commonly used in engineering plastics. Its main components are silica and other derived metal oxides. The current international mainstream production process is the kiln drawing method. According to the alkali content in the glass, it can be divided into alkali-free glass. Glass fiber, medium-alkali glass fiber and high-alkali glass fiber; commonly used glass fibers in engineering plastics are mainly alkali-free chopped glass fibers and untwisted long glass fibers. After adding glass fibers, engineering plastics will have the following changes.
Advantage:
1. Enhance rigidity and hardness. The addition of glass fiber can improve the strength and rigidity of plastic;
2. Improve the heat resistance and heat distortion temperature. Taking nylon as an example, the heat distortion temperature of nylon with glass fiber is increased by at least 30℃. The temperature resistance of general glass fiber reinforced nylon can reach more than 220℃;
3. Improve dimensional stability and reduce shrinkage;
4. Reduce warping deformation;
5. Reduce creep;
6. Reduce hygroscopicity.
Shortcoming:
As the modulus of the product increases, the toughness will decrease; it will have a negative impact on the flame retardant performance, because the candle wick effect will interfere with the flame retardant system and affect the flame retardant effect; exposed glass fiber will reduce the gloss of the surface of the plastic product, etc.
The length of the glass fiber directly affects the brittleness of the material; if the glass fiber is not handled well, the short fiber will reduce the impact strength; if the long fiber is handled well, the impact strength will be increased. In order to prevent the brittleness of the material from greatly decreasing, a certain length of glass fiber must be selected.
The fiber content of the product is also a key issue. The industry generally adopts integer content such as 15%, 25%, 30%, 50%, etc. The specific glass fiber content needs to be determined according to the use of the product.
To obtain good mechanical properties and surface effects, the diameter and length selection of the glass fiber, as well as the surface treatment and glass fiber content during subsequent modification are all crucial!
Calcium Carbonate
Calcium carbonate products are divided into heavy calcium carbonate and light calcium carbonate. Heavy calcium carbonate, referred to as heavy calcium carbonate, or GCC in English, is produced by directly crushing natural calcite, limestone, white sol, shells, etc. using mechanical methods. Since the settling volume of heavy calcium carbonate is smaller than that of light calcium carbonate, it is called heavy calcium carbonate. At present, there are two main processes for industrial production of heavy calcium carbonate, one is dry process and the other is wet process. Dry processes produce lower-cost, more versatile products than wet processes.
Light calcium carbonate is referred to as light calcium, also known as precipitated calcium carbonate, or PCC in English. It is made by calcining raw materials such as limestone to produce lime. The main components are calcium oxide and carbon dioxide. The lime is then added with water to digest the lime to produce lime milk. The main component is calcium hydroxide. , then carbon dioxide is introduced, carbonized lime milk generates calcium carbonate precipitation, and is finally obtained by dehydration, drying and crushing. Or first use sodium carbonate and calcium chloride to perform a metathesis reaction to generate calcium carbonate precipitate, and then make it through dehydration, drying and pulverization.
Calcium carbonate is one of the earliest inorganic fillers used to fill reinforced and toughened PP, and the application of micron-sized calcium carbonate has always been dominant. Studies have shown that the addition of calcium carbonate can increase the impact strength of PP, but reduce the tensile strength. The addition of light calcium carbonate can simultaneously increase the impact strength and yield strength, and the effect of PCC treated with stearic acid is better. , Calcium carbonate treated with titanate coupling agent can significantly improve the impact strength of PP.
With the emergence of nano-scale calcium carbonate, people have found that using nano-calcium carbonate can simultaneously enhance toughening, and the toughening effect is better than micron-scale calcium carbonate. Research shows that the mechanical properties of composite materials are also very different due to different shapes of nano-calcium carbonate. Cubic nano-calcium carbonate is beneficial to improving the impact properties of composite materials, while fibrous nano-calcium carbonate can significantly improve the tensile properties of the material. Nano-calcium carbonate can significantly refine PP spherulites and promote the formation of β-crystalline forms. generate.