Nucleating agent is a functional additive used to change crystallization behavior of polypropylene, then change its crystallization morphology, mechanical properties, thermodynamic properties and optical properties.
1. Polypropylene nucleating agent HBP
Polypropylene modified by adding nucleating agent has characteristics of good transparency, high gloss, excellent mechanical properties and processing properties, and its scope of use is also relatively wide.
2. Polyoxymethylene nucleating agent
Polyoxymethylene (POM) is a high-crystalline engineering plastic with excellent comprehensive properties. It has high strength and hardness, good rigidity, good wear resistance and fatigue resistance, so it is used to replace non-ferrous metals and alloys, is widely used in automobiles, electronics, construction, machinery and other industries. Due to high crystallinity of polyoxymethylene (generally more than 60%), products have gaps, low impact strength and large molding shrinkage, which are not matched with other excellent properties and need further improvement. There are two main ways to improve performance of polyoxymethylene materials: strictly control processing conditions and add nucleating agents. Studies have found that impact strength of crystalline polymers is related to size and distribution of spherulites. Experiment mainly adds nucleating agents to polyoxymethylene to change morphology of polyoxymethylene spherulites, reduce its crystal size and shrinkage during molding process, improve its impact resistance, and optimize performance of polyoxymethylene so that it can meet some special requirements.

During manufacturing, processing, storage and use of plastics such as PP, PE, and PS, oxidative degradation often occurs due to effects of light, oxygen, heat and other factors, causing plastic deterioration, resulting in plastic loss of weather resistance and durability, affecting strength and appearance of plastics. Antioxidants are usually used to extend life of polymer materials and inhibit or delay oxidative degradation of polymers.
1. Primary antioxidant
Primary antioxidant, also known as free radical scavenger, is a type of antioxidant that plays a major role. It can capture oxygen-containing free radicals (·OH, RO·, ROO·) and carbon free radicals (but the effect is poor) generated during thermal oxidation aging of polymers, thereby stopping or slowing down thermal oxidation aging of polymers.
2. Auxiliary antioxidant
Auxiliary antioxidant is also known as hydroperoxide decomposer. It is a type of auxiliary agent that can decompose polymer hydroperoxides generated in thermal oxidation aging chain reaction to produce inactive compounds, thereby stopping or slowing down thermal oxidation aging. Because it often has a synergistic effect with primary antioxidant and can only exert the greatest effect when used in combination with primary antioxidant, it is generally called an auxiliary antioxidant.
3. Carbon free radical scavenger
Carbon free radicals (i.e. alkyl free radicals) are usually generated in chain reaction of thermal oxidation aging in absence of oxygen and at high temperature.

 

Plasticizers are the largest additives in modern plastics industry and play a decisive role in promoting development of plastics industry, especially polyvinyl chloride industry. Any liquid organic compound or low-melting-point solid that can be mixed with resins without chemical changes during mixing, but can reduce glass transition temperature of material and melt viscosity during plastic molding, remain unchanged, or can be retained in plastic products for a long time and change certain physical properties of resin despite chemical changes, is called a plasticizer.
Polyester plasticizers are made from dibasic acids and diols through condensation reactions. Main types are adipic acid polyesters and phthalic anhydride polyesters. The biggest difference between polyester plasticizers and commonly used plasticizers is that they have a larger molecular weight. Molecular weight of polyester plasticizers can be comparable to that of PVC, so they have better compatibility with PVC. Moreover, due to its low volatility, resistance to oil and extraction of aliphatic or aromatic hydrocarbons, resistance to migration in paint and rubber, and excellent aging resistance, compared with low molecular weight plasticizers, polyester plasticizers have superior characteristics such as resistance to extraction, high temperature resistance and low migration, making it known as a "permanent plasticizer" and a rapidly developing type of plasticizer.

1. Thermal Stabilization Mechanism of Rare Earth Thermal Stabilizer
Rare earth elements have numerous orbits that can serve as central ions to accept lone pairs of electrons of ligands. At the same time, rare earth metal ions have a large ionic radius and form ionic bonds with inorganic or organic ligands mainly through electrostatic attraction. HCL released during degradation of PVC has a strong catalytic effect. It is generally believed that it is an ionic catalytic reaction. [CLHCL]- or [CL]- ions participate in reaction process, and [CLHCL]- or [CL]- ions can serve as ligands to provide lone pairs of electrons. According to "soft and hard acid-base principle" proposed by Pearson, hard base chloride ions and rare earth metal ions are easy to form stable complexes. Therefore, there is a strong coordination and complexing ability between rare earth atoms and chlorine atoms on PVC chain. [CLHCL]- and [CL]- no longer participate in catalytic dehydrogenation reaction, which plays a certain stabilizing role on PVC.
2. Thermal stabilization of polyoxymethylene by antioxidant F
Polyoxymethylene (POM) is widely used as an engineering plastic with excellent comprehensive performance. However, due to its special molecular structure, POM has poor thermal stability. During its melt processing, it is easy to break chain under action of heat and oxygen, thermally degrade in a free radical decomposition mode, then a continuous deformaldehyde reaction occurs. Antioxidants are usually added to capture free radicals generated by system, interrupt auto-oxidation cycle of the entire system, and play an antioxidant stabilizing role. At present, phenolic antioxidants with brands of Irganoｘ259 and Irganoｘ245 from Swiss Ciba are commonly used in POM production applications at home and abroad, which can greatly improve thermal stability of POM.
Experimenters selected high relative molecular weight hindered phenolic antioxidant F as POM antioxidant. In addition to playing a high-efficiency thermal stabilizing role, it can also reduce amount of antioxidants and reduce production cost of POM.
1) Results of thermal weight loss rate, thermal weight loss rate, and equilibrium torque analysis show that when dosage of antioxidant F is 0.3~0.4, it can achieve a thermal stabilizing effect on POM that is equivalent to or even better than 0.5% Irganoｘ245.
2) Antioxidant F can effectively inhibit degradation of POM resin caused by heat, oxygen and stress during high-temperature processing, effectively prolong long-term heat and oxygen life of POM products, heat and oxygen stability of a small amount of antioxidant F (0.3%) can reach level of 0.5% Irganox245, which can be promoted and applied to POM production to further improve thermal stability of POM and reduce production costs.

 

When a large amount of plasticizer is added to PVC to make it soft PVC, it is necessary to treat it with flame retardant. In addition to flame retardants, smoke suppression is also an urgent problem that PVC needs to solve.
1) Carefully select flame retardant plasticizers-aryl phosphates and aryl-alkyl phosphates to avoid deteriorating other properties of plastics while increasing flame retardancy, and pay special attention to low-temperature softness of material.
2) Smoke suppressants. Traditional smoke suppressants include molybdenum trioxide, magnesium hydroxide, ammonium octamolybdate, etc. Addition of molybdenum-based smoke suppressants is generally between 2% and 3%, which can reduce amount of smoke by 30% to 80%. If used in combination with ATH, magnesium hydroxide or calcium carbonate, it will have a better effect.

ACR processing aids are a type of polymer-based additives that improve plasticizing processing performance of plastics (mainly PVC). They are usually high molecular weight polymers copolymerized by methyl methacrylate (MMC) and acrylate emulsion (or contain a small amount of other ingredients such as styrene). During PVC processing process, ACR processing aids promote PVC plasticization by increasing transfer of heat and shear force, and make melt uniform. At the same time, ACR processing aids have good compatibility with PVC. During processing process, high molecular weight ACR molecular chains can be inserted between PVC molecular chains, playing a "tangling" role, which can significantly improve viscosity and elasticity of PVC melt.
At present, use of in-situ polymerization technology and introduction of inorganic nanoparticles can truly improve application performance of ACR processing aids and performance of PVC.