Polypropylene (PP) has been widely used due to its good mechanical properties, non-toxicity, low relative density, heat resistance, chemical resistance, low cost, and easy processing. However, PP is a partially crystalline resin. The spherulites obtained under normal production conditions are bulky, the crystallization is imperfect, and there is a large light scattering at the interface of the spherulites, resulting in a decrease in transparency of the product, in order to satisfy certain products. For the transparency requirements, the PP needs to be transparently modified. Compared with some other commonly used transparent materials, transparent PP has transparency, excellent gloss, light weight and low cost, good rigidity and comprehensive performance, and can be recycled and has a high heat distortion temperature (generally greater than 110 ° C). A wide range of applications.
1 Production technology of transparent PP
At present, there are three main types of industrialized transparent PP production technologies: (1) adding a transparent nucleating agent to the PP resin; (2) producing a random copolymerized PP using a ZN catalyst; and (2) producing a highly transparent PP using a metallocene catalyst. .
2 Types and applications of transparent PP nucleating agents
2.1 inorganic transparent nucleating agent
Inorganic transparent nucleating agents mainly refer to talc, silica, mica and the like. Such transparent nucleating agents are cheap and easy to obtain, and a small amount of use can improve the transparency of the product, but it is difficult to disperse in PP and has a shielding effect on light. Too much amount affects the transparency of the product, thus limiting its application.
Nucleation mechanism of such nucleating agent: When PP is crystallized from the melt, the surface of the nucleating agent acts as an electron donor to form a hydrogen bond with the methyl group of PP, and the PP platelet molecular chain grows on the surface of the nucleating agent in PP. A transgranular region is formed between the surface of the melt and the nucleating agent. X-ray diffraction studies indicate that the PPα axis is oriented along the crystal growth direction, and the b-axis is consistent with the c-axis of the nucleating agent; the unit cell structure of the nucleating agent and the PP The unit cell structure is consistent.
DeMedeiros et al. found that talc is a highly efficient nucleating agent through the dynamic crystallization of the isotactic PP/talc system. With the increase of the amount of nucleating agent, the nucleation efficiency and crystallization temperature increase, but at a high cooling rate. Nuclear efficiency has declined.
2.2 Organic transparent nucleating agent
2.2.1 aryl phosphate transparent nucleating agent
This type of nucleating agent was first developed by Japan's Asahi Chemical Company. According to the different development years, it can be divided into three generations: the first generation products are represented by NA-10 [sodium (2,4-di-tert-butylphenyl)phosphate], which was introduced in the early 1980s; the second generation products It was introduced in the mid-1980s and is represented by NA-11[2,2'-methylene-bis(4,6-di-n-butylphenol) sodium phosphate; the third generation product was developed in recent years. Typically represented by NA-21 [methylene bis(2,4-di-tert-butylphenyl)aluminum phosphate), it has a lower melting point, better dispersion in PP, and higher nucleation efficiency.
Due to the complex structure of such nucleating agents, little research has been done on their nucleation mechanism, which has not been determined so far. Yoshimoto et al. studied the effect of NA-11 on PP crystallization and found that when PP crystallizes from the melt, NA-11 initiates epigenetic crystallization of the PP segment, which is mainly along the surface perpendicular to the edge of the nucleating agent. At the top, when epiphytic crystallization occurs, the nucleation free energy decreases and the nucleation rate increases.
Marco et al. used differential scanning calorimetry (DSC) to study the nucleation efficiency of organophosphate nucleating agents in isotactic PP and found that the crystallization peak temperature of nucleating PP can be significantly improved even at very low dosages. However, the crystallization peak temperature does not change significantly at higher dosages. The addition of nucleating agent can improve the crystal structure of PP, reduce the rearrangement of PP segments, increase the dimensional stability of products at high temperatures, and expand the application range of products. Gui et al. studied the effects of organophosphate nucleating agents on isotactic PP crystallization and mechanical behavior. They found that when the amount of nucleating agent increased from 0 to 0.8% (mass fraction, the same below), the tensile strength and flexural strength of PP increased by 15% after nucleation, the elastic modulus increased by 35%, and the crystallization peak temperature increased. 10 ° C, but when the amount of nucleating agent is more than 0.2%, the crystallization peak temperature does not change significantly. The density of crystal nuclei in the system increased by 106 times, and the mechanical properties increased with the increase of the amount of nucleating agent, and the logarithm of the density of crystal nuclei was linear.
Gahleitner et al. studied the effect of nucleating agents on shear-induced PP crystallization. They added three different commercial nucleating agents to three different PPs: talc, Millad3988, NA-11, and examined nucleating agents and foundations. The effect of the resin on the shear-induced crystal structure, it is found that the properties of the nucleating agent and the base resin have a great influence on the nucleation efficiency, especially the mechanical and optical properties, and the processing and the shape of the part have great final properties. Impact.
Wang et al. studied the isothermal crystallization and melting characteristics of injection molded samples containing isotactic PP of NA-11 and NC-4 [a DBS (dibenzylidene) nucleating agent], and found that PP crystallization after nucleation The cycle is shortened, and the PP crystal after nucleation is more perfect. According to the size of the semi-crystallization period, NA-11 has higher efficiency than NC-4.
2.2.2 Sorbitol transparent nucleating agent
DBS nucleating agents are currently the most widely used organic nucleating agents in the world. According to the difference of substituents, it is also divided into three generations: the first generation DBS nucleating agent has no substituents on the benzene ring, and the representative varieties include Milled 3905 of foreign Milliken Company and TM-1 of Shanxi Institute of Chemical Industry. The cost of the agent is low, the nucleation effect is general, the temperature is unstable, the degradation is easy to release the parent aldehyde, and the market application is limited; the second generation product is characterized by the substitution of the benzene ring by a group such as chlorine or methyl group, which increases The permeability has been greatly improved, but the smell is still very large, representing Milliken's Millad3940 and domestic TM-2; recently Milliken developed the third generation of Millad3988, its performance has been greatly improved. It can be used for transparent products under general or harsh conditions. It is the most excellent variety of DBS nucleating agents. The domestic nucleating agents mainly include SKYC-5988 and Shanxi Institute of Chemical Industry of Songxi Nanhai Chemical Co., Ltd. TM-6 and Yantai only Chu Synthesis Chemical Co., Ltd. ZC-3.
Due to the wide application of such nucleating agents, many studies on their nucleation mechanism have been widely recognized. When PP is crystallized, when two free hydroxyl groups of DBS are above the melting point of PP, a three-dimensional nanomesh is formed by hydrogen bonding. The structure, the specific surface area is increased, and a gel phenomenon occurs, thereby generating a large number of crystal nuclei and increasing the crystallization rate.
Wong et al. studied the effects of three sorbitol nucleating agents on the optical properties and mechanical properties of isotactic PP. It was found that the concentration of three different nucleating agents (mass fraction 0.15%, 0.25%, 0.35%) and screw were changed. The rotational speed, the transparency of PP increases with the increase of the concentration of nucleating agent, the addition of nucleating agent does not necessarily improve the PP impact strength, but the tangent modulus of the sample becomes larger with the increase of the amount of nucleating agent, at the high screw The overall mechanical properties are improved at the rotational speed but the optical properties of the article are impaired and the density of the part is increased.
Gahleitner et al. found that the random copolymerization of PP with sorbitol as a nucleating agent has the best transparency, which they attribute to the formation of a large number of gamma crystals.
Chen Hong et al. found that the addition of transparent nucleating agent Millad3988 significantly improved the transparency of random copolymer PP, and the change of ethylene content will affect the performance of transparent PP with a transparency of 1% ethylene. When the mass fraction is the same as the above, there is a turning point. When the ethylene content is more than 3%, the transparency and other properties of the random PP are good.
For the first time, Supaphol et al. studied the effects of adding different nucleating agents on the crystallization and mechanical properties of syndiotactic PP (SPP), adding an inorganic nucleating agent with a mass fraction of 5% and a mass fraction of 1% in SPP. Organic nucleating agents were investigated for their effects on the crystallization behavior of SPP. It was found that the nucleating effect of these nucleating agents on SPP decreased according to the following rules: DBS, talc, MDBS [bis(p-methyldibenzylidene) Yamanashi Alcohol], SiO2, kaolin, DMDBS [bis(3,4-dimethyldibenzylidene) sorbitol], marl, TiO2. These nucleating agents increase the crystallization ability of SPP to varying degrees. Different nucleating agents have different effects on the mechanical properties of PP. Inorganic nucleating agents increase the Young's modulus of PP, but organic nucleating agents are reduced. Young's modulus of PP. Since the interface between the matrix resin and the nucleating agent particles is not strong, the impact strength of the PP after nucleation decreases.
2.2.3 Carboxylic acid metal salt transparent nucleating agent
Khanna et al. studied the nucleation mechanism of such nucleating agents. It is believed that the crystallization of nucleating PP is the epitaxial growth of PP molecular segments along the surface of the nucleating agent. The side methyl groups in the helical structure of PP are arranged in the benzene ring of the nucleating agent. Above, the main chain interacts with the surface of the nucleating agent benzene ring to crystallize.
Luo Zhixing et al. added hydroxyaluminum tert-butylbenzoate (Al-PTBBA to isotactic PP and found that the nucleation efficiency was the highest when the mass fraction was 0.3%, and the crystallization temperature of PP increased by 10-15 °C after nucleation, but Al - PTBBA is poorly dispersed in PP, and grinding helps to disperse. Combined with talc, it can improve nucleation.
Xu et al. systematically studied the effect of nucleating agent on the impact strength of isotactic PP crystal morphology and crystal morphology. They used sodium benzoate as a nucleating agent and found that the number of small spherulites increased with the increase of the amount of nucleating agent. The radius distribution is narrowed and the unit cell parameters are reduced.
2.2.4 Dehydroabietic acid and its salts transparent nucleating agent
In order to overcome the high cost of the above-mentioned several types of nucleating agents, the odor and yellowing of the products after the addition, in 1995, Arakawa Corporation of Japan developed a new class of nucleating agent, rosin acid nucleating agent. Since the raw material of such nucleating agent is derived from the natural product rosin, it is tasteless, non-toxic, non-irritating, highly bio-safe, and has no pollution to the environment, completely overcoming the interpretation of the DBS-type nucleating agent during use. The problem of releasing the parent aldehyde to produce an odor can be widely applied to cosmetic packaging, food packaging, medical packaging, etc., and is a new type of plastic processing aid with excellent performance. The earliest commercialized nucleating agent was Pinecrystal KM-1300 and KM-1500 from Arakawa, Japan. KM-1500 has better mechanical properties than KM-1300. In 1999, KM-1300 replaced KM-. 1600, nucleation efficiency is higher.
LiChun-cheng et al. developed a nucleating agent with natural rosin as the starting material. It was found that this kind of nucleating agent can effectively reduce the spherulite size of PP, reduce the haze of the product, and improve the transparency, heat distortion temperature and crystallization of the product. The temperature shortens the molding cycle of the article and can improve the mechanical properties of the article, particularly the modulus of elasticity, and the notched impact strength of the article rises due to the fine grain strengthening effect. And the transparent PP made is non-toxic, tasteless and can be used for medicine and food packaging. The addition of a nucleating agent increases the free energy of the PP nucleation interface, but it increases the number of nuclei in the system, thereby increasing the overall crystallization rate.
WangHui et al studied the effects of dehydroabietic acid, dehydrochlorinated potassium citrate and dehydroabietate co-crystals on the crystallization process and properties of PP. It was found that this eutectic ratio uses dehydrochlorinated or potassium dehydroabietate alone. The efficiency is higher, the crystallization temperature and heat distortion temperature of the product after nucleation are improved, the mechanical properties are improved, the spherulite size is reduced, and the transparency is improved.
2.2.5 branched amide transparent nucleating agent
Blomenhofer et al. reported a new organic transparent nucleating agent. This is a new type of branched amide transparent nucleating agent characterized by a symmetrical star-substituted phenyl amide in the center, and the branch can be adjusted as needed. The transparent modification effect of such nucleating agents is very significant, but the different effects of the starting monomers are slightly different; different substituents have different effects. When other groups are the same, the attachment mode of the amide group has a great influence on the nucleation effect. When the nitrogen atom in the amide is directly attached to the benzene ring, the effect of transparent modification is best, and the nitrogen atom attached to the benzene ring is more The better the transparency modification effect, the better the transparency modification effect of 1,3,5-tri-tert-butylamide benzene. The nucleating agent has better transparency modification effect than DMDBS. When the dosage is 0.15% (mass fraction), the haze of PP is reduced by 50%-70%, and the crystallization starting temperature is increased by 6-14 °C. Moreover, such nucleating agents have solved the problems that generally plague the dispersion of the former nucleating agents in the matrix resin, causing yellowing of the product and odor of the product, and thus have received extensive attention.
2.3 polymer type transparent nucleating agent
The essence of polymer nucleating agents are some high melting point polymers, mainly polyvinylcycloalkane compounds. The main varieties are polyvinylcyclobutane, polyvinylcyclohexane and polyvinylcyclopentane. , polyvinyl-2-methylcyclohexane, poly-3-methyl-1-butene, and the like.
Lee et al. added a series of polymers as nucleating agents to isotactic PP to study the effect on PP crystallization. The results show that polycyclopentene has the best effect and its nucleation effect is better than typical organic nucleation. With the addition of polycyclopentene, the crystallization temperature and crystallinity of PP increased, the crystallization rate increased, the spherulite volume decreased significantly, and the transparency increased remarkably. It is also found that the nucleating agent does not have to exist in a solid form in the matrix, and the interaction between the nucleating agent and the matrix has a great influence on improving the nucleation efficiency.
Despite the attractive prospects of polymeric nucleating agents, commercial products have not yet been available, and are only found in some patent reports. Due to the complex structure and mechanism of action of such nucleating agents, no research reports on its nucleation mechanism have been reported so far.
3 Conclusion
With the recognition of transparent PP in the market, the transparent modification of PP is one of the hot spots of modification at present. Due to its low cost, it can be processed on traditional molding equipment, transparent PP and traditional transparent material poly-p-benzene. Compared with ethylene glycol diester (PET) and the like, the demand is increasing. At present, there are many general low-performance PP varieties in China, and the market tends to be saturated. However, the high-value-added and high-transparency PP production is less, which is lagging behind the research and development of domestic transparent nucleating agents, and is very comparable with foreign advanced levels. The big gap has a close relationship. Therefore, based on China's national conditions, it is of great practical significance to develop some transparent, nucleating agents with high efficiency, multi-function and low cost.
1 Production technology of transparent PP
At present, there are three main types of industrialized transparent PP production technologies: (1) adding a transparent nucleating agent to the PP resin; (2) producing a random copolymerized PP using a ZN catalyst; and (2) producing a highly transparent PP using a metallocene catalyst. .
2 Types and applications of transparent PP nucleating agents
2.1 inorganic transparent nucleating agent
Inorganic transparent nucleating agents mainly refer to talc, silica, mica and the like. Such transparent nucleating agents are cheap and easy to obtain, and a small amount of use can improve the transparency of the product, but it is difficult to disperse in PP and has a shielding effect on light. Too much amount affects the transparency of the product, thus limiting its application.
Nucleation mechanism of such nucleating agent: When PP is crystallized from the melt, the surface of the nucleating agent acts as an electron donor to form a hydrogen bond with the methyl group of PP, and the PP platelet molecular chain grows on the surface of the nucleating agent in PP. A transgranular region is formed between the surface of the melt and the nucleating agent. X-ray diffraction studies indicate that the PPα axis is oriented along the crystal growth direction, and the b-axis is consistent with the c-axis of the nucleating agent; the unit cell structure of the nucleating agent and the PP The unit cell structure is consistent.
DeMedeiros et al. found that talc is a highly efficient nucleating agent through the dynamic crystallization of the isotactic PP/talc system. With the increase of the amount of nucleating agent, the nucleation efficiency and crystallization temperature increase, but at a high cooling rate. Nuclear efficiency has declined.
2.2 Organic transparent nucleating agent
2.2.1 aryl phosphate transparent nucleating agent
This type of nucleating agent was first developed by Japan's Asahi Chemical Company. According to the different development years, it can be divided into three generations: the first generation products are represented by NA-10 [sodium (2,4-di-tert-butylphenyl)phosphate], which was introduced in the early 1980s; the second generation products It was introduced in the mid-1980s and is represented by NA-11[2,2'-methylene-bis(4,6-di-n-butylphenol) sodium phosphate; the third generation product was developed in recent years. Typically represented by NA-21 [methylene bis(2,4-di-tert-butylphenyl)aluminum phosphate), it has a lower melting point, better dispersion in PP, and higher nucleation efficiency.
Due to the complex structure of such nucleating agents, little research has been done on their nucleation mechanism, which has not been determined so far. Yoshimoto et al. studied the effect of NA-11 on PP crystallization and found that when PP crystallizes from the melt, NA-11 initiates epigenetic crystallization of the PP segment, which is mainly along the surface perpendicular to the edge of the nucleating agent. At the top, when epiphytic crystallization occurs, the nucleation free energy decreases and the nucleation rate increases.
Marco et al. used differential scanning calorimetry (DSC) to study the nucleation efficiency of organophosphate nucleating agents in isotactic PP and found that the crystallization peak temperature of nucleating PP can be significantly improved even at very low dosages. However, the crystallization peak temperature does not change significantly at higher dosages. The addition of nucleating agent can improve the crystal structure of PP, reduce the rearrangement of PP segments, increase the dimensional stability of products at high temperatures, and expand the application range of products. Gui et al. studied the effects of organophosphate nucleating agents on isotactic PP crystallization and mechanical behavior. They found that when the amount of nucleating agent increased from 0 to 0.8% (mass fraction, the same below), the tensile strength and flexural strength of PP increased by 15% after nucleation, the elastic modulus increased by 35%, and the crystallization peak temperature increased. 10 ° C, but when the amount of nucleating agent is more than 0.2%, the crystallization peak temperature does not change significantly. The density of crystal nuclei in the system increased by 106 times, and the mechanical properties increased with the increase of the amount of nucleating agent, and the logarithm of the density of crystal nuclei was linear.
Gahleitner et al. studied the effect of nucleating agents on shear-induced PP crystallization. They added three different commercial nucleating agents to three different PPs: talc, Millad3988, NA-11, and examined nucleating agents and foundations. The effect of the resin on the shear-induced crystal structure, it is found that the properties of the nucleating agent and the base resin have a great influence on the nucleation efficiency, especially the mechanical and optical properties, and the processing and the shape of the part have great final properties. Impact.
Wang et al. studied the isothermal crystallization and melting characteristics of injection molded samples containing isotactic PP of NA-11 and NC-4 [a DBS (dibenzylidene) nucleating agent], and found that PP crystallization after nucleation The cycle is shortened, and the PP crystal after nucleation is more perfect. According to the size of the semi-crystallization period, NA-11 has higher efficiency than NC-4.
2.2.2 Sorbitol transparent nucleating agent
DBS nucleating agents are currently the most widely used organic nucleating agents in the world. According to the difference of substituents, it is also divided into three generations: the first generation DBS nucleating agent has no substituents on the benzene ring, and the representative varieties include Milled 3905 of foreign Milliken Company and TM-1 of Shanxi Institute of Chemical Industry. The cost of the agent is low, the nucleation effect is general, the temperature is unstable, the degradation is easy to release the parent aldehyde, and the market application is limited; the second generation product is characterized by the substitution of the benzene ring by a group such as chlorine or methyl group, which increases The permeability has been greatly improved, but the smell is still very large, representing Milliken's Millad3940 and domestic TM-2; recently Milliken developed the third generation of Millad3988, its performance has been greatly improved. It can be used for transparent products under general or harsh conditions. It is the most excellent variety of DBS nucleating agents. The domestic nucleating agents mainly include SKYC-5988 and Shanxi Institute of Chemical Industry of Songxi Nanhai Chemical Co., Ltd. TM-6 and Yantai only Chu Synthesis Chemical Co., Ltd. ZC-3.
Due to the wide application of such nucleating agents, many studies on their nucleation mechanism have been widely recognized. When PP is crystallized, when two free hydroxyl groups of DBS are above the melting point of PP, a three-dimensional nanomesh is formed by hydrogen bonding. The structure, the specific surface area is increased, and a gel phenomenon occurs, thereby generating a large number of crystal nuclei and increasing the crystallization rate.
Wong et al. studied the effects of three sorbitol nucleating agents on the optical properties and mechanical properties of isotactic PP. It was found that the concentration of three different nucleating agents (mass fraction 0.15%, 0.25%, 0.35%) and screw were changed. The rotational speed, the transparency of PP increases with the increase of the concentration of nucleating agent, the addition of nucleating agent does not necessarily improve the PP impact strength, but the tangent modulus of the sample becomes larger with the increase of the amount of nucleating agent, at the high screw The overall mechanical properties are improved at the rotational speed but the optical properties of the article are impaired and the density of the part is increased.
Gahleitner et al. found that the random copolymerization of PP with sorbitol as a nucleating agent has the best transparency, which they attribute to the formation of a large number of gamma crystals.
Chen Hong et al. found that the addition of transparent nucleating agent Millad3988 significantly improved the transparency of random copolymer PP, and the change of ethylene content will affect the performance of transparent PP with a transparency of 1% ethylene. When the mass fraction is the same as the above, there is a turning point. When the ethylene content is more than 3%, the transparency and other properties of the random PP are good.
For the first time, Supaphol et al. studied the effects of adding different nucleating agents on the crystallization and mechanical properties of syndiotactic PP (SPP), adding an inorganic nucleating agent with a mass fraction of 5% and a mass fraction of 1% in SPP. Organic nucleating agents were investigated for their effects on the crystallization behavior of SPP. It was found that the nucleating effect of these nucleating agents on SPP decreased according to the following rules: DBS, talc, MDBS [bis(p-methyldibenzylidene) Yamanashi Alcohol], SiO2, kaolin, DMDBS [bis(3,4-dimethyldibenzylidene) sorbitol], marl, TiO2. These nucleating agents increase the crystallization ability of SPP to varying degrees. Different nucleating agents have different effects on the mechanical properties of PP. Inorganic nucleating agents increase the Young's modulus of PP, but organic nucleating agents are reduced. Young's modulus of PP. Since the interface between the matrix resin and the nucleating agent particles is not strong, the impact strength of the PP after nucleation decreases.
2.2.3 Carboxylic acid metal salt transparent nucleating agent
Khanna et al. studied the nucleation mechanism of such nucleating agents. It is believed that the crystallization of nucleating PP is the epitaxial growth of PP molecular segments along the surface of the nucleating agent. The side methyl groups in the helical structure of PP are arranged in the benzene ring of the nucleating agent. Above, the main chain interacts with the surface of the nucleating agent benzene ring to crystallize.
Luo Zhixing et al. added hydroxyaluminum tert-butylbenzoate (Al-PTBBA to isotactic PP and found that the nucleation efficiency was the highest when the mass fraction was 0.3%, and the crystallization temperature of PP increased by 10-15 °C after nucleation, but Al - PTBBA is poorly dispersed in PP, and grinding helps to disperse. Combined with talc, it can improve nucleation.
Xu et al. systematically studied the effect of nucleating agent on the impact strength of isotactic PP crystal morphology and crystal morphology. They used sodium benzoate as a nucleating agent and found that the number of small spherulites increased with the increase of the amount of nucleating agent. The radius distribution is narrowed and the unit cell parameters are reduced.
2.2.4 Dehydroabietic acid and its salts transparent nucleating agent
In order to overcome the high cost of the above-mentioned several types of nucleating agents, the odor and yellowing of the products after the addition, in 1995, Arakawa Corporation of Japan developed a new class of nucleating agent, rosin acid nucleating agent. Since the raw material of such nucleating agent is derived from the natural product rosin, it is tasteless, non-toxic, non-irritating, highly bio-safe, and has no pollution to the environment, completely overcoming the interpretation of the DBS-type nucleating agent during use. The problem of releasing the parent aldehyde to produce an odor can be widely applied to cosmetic packaging, food packaging, medical packaging, etc., and is a new type of plastic processing aid with excellent performance. The earliest commercialized nucleating agent was Pinecrystal KM-1300 and KM-1500 from Arakawa, Japan. KM-1500 has better mechanical properties than KM-1300. In 1999, KM-1300 replaced KM-. 1600, nucleation efficiency is higher.
LiChun-cheng et al. developed a nucleating agent with natural rosin as the starting material. It was found that this kind of nucleating agent can effectively reduce the spherulite size of PP, reduce the haze of the product, and improve the transparency, heat distortion temperature and crystallization of the product. The temperature shortens the molding cycle of the article and can improve the mechanical properties of the article, particularly the modulus of elasticity, and the notched impact strength of the article rises due to the fine grain strengthening effect. And the transparent PP made is non-toxic, tasteless and can be used for medicine and food packaging. The addition of a nucleating agent increases the free energy of the PP nucleation interface, but it increases the number of nuclei in the system, thereby increasing the overall crystallization rate.
WangHui et al studied the effects of dehydroabietic acid, dehydrochlorinated potassium citrate and dehydroabietate co-crystals on the crystallization process and properties of PP. It was found that this eutectic ratio uses dehydrochlorinated or potassium dehydroabietate alone. The efficiency is higher, the crystallization temperature and heat distortion temperature of the product after nucleation are improved, the mechanical properties are improved, the spherulite size is reduced, and the transparency is improved.
2.2.5 branched amide transparent nucleating agent
Blomenhofer et al. reported a new organic transparent nucleating agent. This is a new type of branched amide transparent nucleating agent characterized by a symmetrical star-substituted phenyl amide in the center, and the branch can be adjusted as needed. The transparent modification effect of such nucleating agents is very significant, but the different effects of the starting monomers are slightly different; different substituents have different effects. When other groups are the same, the attachment mode of the amide group has a great influence on the nucleation effect. When the nitrogen atom in the amide is directly attached to the benzene ring, the effect of transparent modification is best, and the nitrogen atom attached to the benzene ring is more The better the transparency modification effect, the better the transparency modification effect of 1,3,5-tri-tert-butylamide benzene. The nucleating agent has better transparency modification effect than DMDBS. When the dosage is 0.15% (mass fraction), the haze of PP is reduced by 50%-70%, and the crystallization starting temperature is increased by 6-14 °C. Moreover, such nucleating agents have solved the problems that generally plague the dispersion of the former nucleating agents in the matrix resin, causing yellowing of the product and odor of the product, and thus have received extensive attention.
2.3 polymer type transparent nucleating agent
The essence of polymer nucleating agents are some high melting point polymers, mainly polyvinylcycloalkane compounds. The main varieties are polyvinylcyclobutane, polyvinylcyclohexane and polyvinylcyclopentane. , polyvinyl-2-methylcyclohexane, poly-3-methyl-1-butene, and the like.
Lee et al. added a series of polymers as nucleating agents to isotactic PP to study the effect on PP crystallization. The results show that polycyclopentene has the best effect and its nucleation effect is better than typical organic nucleation. With the addition of polycyclopentene, the crystallization temperature and crystallinity of PP increased, the crystallization rate increased, the spherulite volume decreased significantly, and the transparency increased remarkably. It is also found that the nucleating agent does not have to exist in a solid form in the matrix, and the interaction between the nucleating agent and the matrix has a great influence on improving the nucleation efficiency.
Despite the attractive prospects of polymeric nucleating agents, commercial products have not yet been available, and are only found in some patent reports. Due to the complex structure and mechanism of action of such nucleating agents, no research reports on its nucleation mechanism have been reported so far.
3 Conclusion
With the recognition of transparent PP in the market, the transparent modification of PP is one of the hot spots of modification at present. Due to its low cost, it can be processed on traditional molding equipment, transparent PP and traditional transparent material poly-p-benzene. Compared with ethylene glycol diester (PET) and the like, the demand is increasing. At present, there are many general low-performance PP varieties in China, and the market tends to be saturated. However, the high-value-added and high-transparency PP production is less, which is lagging behind the research and development of domestic transparent nucleating agents, and is very comparable with foreign advanced levels. The big gap has a close relationship. Therefore, based on China's national conditions, it is of great practical significance to develop some transparent, nucleating agents with high efficiency, multi-function and low cost.
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