Hu Sheng18818991823492864690
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0. preface
Polycarbonate (PC) has many advantages, such as high impact strength, good creep resistance and dimensional stability, heat resistance, transparency, low water absorption, non-toxicity and excellent dielectric properties. Widely used in electronic and electrical, automobile industry, medical equipment, construction, lighting appliances and other fields. However, PC also has some shortcomings, such as poor processing rheology, easy cracking, notch sensitivity, easy wear, poor chemical resistance and high price. [ 1]
In order to overcome the shortcomings of PC, it is generally necessary to modify PC, and * * * mixed modification is one of the commonly used methods to modify polymers. As long as the compatibility between PC and other polymers is solved, PC and other polymers have a macroscopic uniform and microscopic separation morphological structure, that is, a partially compatible system with strong interface effect is formed, and some complementary polymers are added, which can solve some shortcomings of PC and give PC some special functions and reduce costs.
1. polystyrene (PS)*** mixed modified polycarbonate (PC)
The glass transition temperature (Tg) of PC/PS composite system was analyzed by differential scanning calorimetry (DSC) (see table 1).
Table 1. Analysis of DSC spectrum of PC/PS composite system [2]
PC/PS(wt %) PS Tg PC Tg difference
0/ 100 92.0
60/40 106.2 144.6 28.4
80/20 105.2 148.6 43.4
90/ 10 103.4 15 1.6 48.2
100/0 154.6
With the addition of PS, the Tg of PC decreased and the Tg of PS increased. The Tg of * * * mixed system is close, which indicates that PC/PS*** mixed system is partially compatible. Cai Qiongying et al. [3] measured the density and linear expansion coefficient of PC/PS composite system with different proportions, and found that their values were lower than the linear sum. The mixture of PC/PS*** is partially compatible, resulting in an intermediate layer between the phase interfaces, which increases the adhesion of the phase interfaces and reduces or eliminates the gaps at the phase interfaces. Through scanning electron microscope (SEM) analysis, it was found that PS microspheres were densely embedded in PC matrix. The mechanical properties of the system were analyzed by Xu Chengzhi and others [2], and it was found that when the PS content was in the range of 15% (mass ratio), the notch and notch impact strength of * * * mixture were higher than that of pure PC, and the peak value appeared when the PS content was about 6-8%. The tensile strength of * * * mixture with PS content less than 20% (mass ratio) is also higher than that of pure PC, and the maximum value appears when PS content reaches 5%, which shows that PS has achieved the dual effects of strengthening and toughening. Xu Weibing et al. [4] studied the rheological behavior of PC/PS composite system. The viscous flow activation energy of PC is 64.64KJ/m2, and when the mass ratio of PC/PS is 95/5, the viscous flow activation energy of the system is 45. 1 1KJ/m2. The addition of PS improves the time dependence of PC processing. At the same time, it is found that the apparent viscosity ηa of * * * mixed system decreases with the increase of shear rate dγ/dt, and the apparent viscosity decreases more obviously at high shear rate, that is to say, the system is more non-Newtonian at high shear rate, and the addition of PS improves the shortcoming that PC is difficult to process.
Liang Li et al. [5] used polyethylene grafted zinc maleate (PE-g-MAZn) ionomer as compatibilizer for PC/PS system. The ionic content and concentration of ionomer have a great influence on the Tg change of PC. The higher the grafting rate and the more dosage, the better the compatibilization effect. When the content of ionomer exceeds 5% (mass percentage), it has little effect on the compatibilization effect of the system. Xu Weiqiang et al. [6][7] used 2- ethylene -2- oxazoline-styrene (RPS) to compatibilize PC/PS system in situ, and measured the mechanical properties of PC/PS/RPS composite system, as shown in Table 2.
Table 2. Mechanical properties of PC/PS/RPS composite system
PC/PS/RPS(wt%) bending strength (MPa) impact strength (KJ/m2) tensile strength (MPa)
7/3/0 53.5 12 53.6
7/2.5/0.5 84.2 3 1 58.0
7/2.25/0.75 93.8 35 57.9
7/2/ 1 1 18.2 33 57.3
7/ 1.75/ 1.25 92.2 36 6 1.3
7/ 1.5/ 1.5 88.9 27 50.2
It can be seen that the addition of RPS improves the adhesion between the two interfaces. When the content of RPS is 65,438+00%, the bending strength and impact strength are increased by 65,438+0,265,438+0% and 65,438+0.75% respectively. At this time, the compatibilization effect is the most obvious. DSC analysis showed that the addition of RPS made the difference of Tg between PC and PS smaller, and phase contrast microscope analysis showed that the addition of RPS significantly reduced the particle size of dispersed phase PS and improved the compatibility of PC/PS composite system.
PC-g-PS grafted polymer is another good compatibilizer for PC/PS system. Hui Zhongzhi [8] studied the rheological behavior of PC/PS/PC-g-PS composite system. The melt of PC/PS*** mixture is pseudoplastic fluid. The addition of PC-g-PS can reduce the apparent viscosity and improve the properties of composites. Apparent viscosity changes slowly, and the content of PC-g-PS in the range of 5- 15 wt% (PC/PS is 70/30 wt) has little effect on shear rate and apparent viscosity. In some cases, the polymer is required to have excellent optical properties, especially when it is used as the carrier or transmission medium of optical information recording materials (such as laser discs or optical lenses), the smaller birefringence will cause greater optical information distortion. Generally speaking, the greater the degree of orientation of polymer chains, the more biased the birefringence, and the orientation problem will be difficult to eliminate. However, mixing positive and negative birefringence materials may eliminate birefringence and form so-called "zero birefringence materials". The refractive indices of PC and PS are 1.586 and 1.590, respectively, and their reflectivity is only 4.9%, so the light intensity loss caused by reflection is very small, so both of them are often used as optical materials. Moreover, PC is a positive birefringence material (birefringence is 0. 106) and PS is a negative birefringence material (birefringence is -0. 10), and the two materials are mixed. Because their refractive indices are very close, the birefringence effect can be partially offset without affecting the light transmittance. When PC/PS is about 40/60(wt), [9] Pu et al. [10] were also analyzed by DSC, SEM and density gradient method, which showed that PC-g-PS had a good compatibilization effect on PC/PS*** mixed system, and the adhesion of PC/PS interface was enhanced and the interphase was closely packed. With the addition of PS, the impact strength of the composite system is greatly reduced, the hardness is increased, the water absorption is reduced, and the solvent cracking resistance is increased.
2. Polyethylene (PE)*** mixed modified PC
The types of polyethylene are high density polyethylene, low density polyethylene and LLDPE. PE is a nonpolar crystalline polymer, while PC is a polar amorphous polymer. There are great differences between them in morphology and structure. The solubility parameter of the former is (5.8KJ/m3) 1/2, and the solubility parameter of the latter is 20.3(KJ/m3) 1/2, so PC/PE is extremely polar. [ 1 1]
Feng et al. [12] studied the impact fracture of PC/HDPE composite system. SEM analysis shows that PC impact fracture belongs to semi-ductile-semi-brittle fracture, and PC/PE alloy belongs to ductile fracture. With the addition of HDPE, the impact strength of PC with sharp notch is increased from 7.2KJ/m2 to 46.9KJ/m2(PC/PE is 100/7 wt). Hu Shengwei [13] found that in PC/HDPE system, the addition of PE promoted the existence of external PE layered structure and improved the water resistance and solvent resistance of PC. At the same time, due to the dilution and internal lubrication of PE to PC, the processing rheological properties of the composite system are improved.
Xu Weibing et al. [14] used ethylene-acetic acid * * * polymer (EVA) as compatibilizer, which greatly improved the compatibility of PC/PE system. The addition of EVA decreased the sensitivity of PC to notch impact damage, and the viscous flow activation energy of the system decreased from 64.9KJ/mol to 5 1.0 kJ/mol(PE content was 5wt%). When Tang Song Deng Chao [15] used maleic anhydride (MAH) grafted LLDPE to modify PC, it was found that the mechanical properties of the system were much better than that of the simple PC/LLDPE*** blend (see Table 3).
Table 3. Mechanical properties of PC and PC/PE * * *
Charpy notch impact strength (KJ/m2) cantilever impact strength (KJ/m2) tensile strength (MPa)
Computer 2 1.2 87. 1 50.5
Personal computer /LLDPE(93/7)
PC/LLDPE-g-MAH(93/7)63.6 5 10.0 5 1. 1
Due to the transesterification reaction in the mixing process of PC/PE-g-MAH system, the binding force of the system was increased and the compatibility of the two systems was improved [16], so the PC/PE-g-MAH system showed excellent macro-properties.
Li Huaxing et al. [17] used maleic anhydride ethylene propylene diene monomer (MEPDM) as compatibilizer for PC/PE, and found that some particles remained in the impact section of MEPDM, which played the role of "nail anchor", thus enhancing the two-phase force. At the same time, with the addition of MEPDM, the crystallinity of LDPE decreased, the disordered region of LDPE increased, and the entanglement with PC substrate increased. When too much MEPDM is added, it will be dissociated from the PC substrate, but its toughness will be reduced due to its low strength. The suitable dosage of MEPDM is 1.5 phr. Grafts of LDPE, such as allyl bisphenol A ether grafted LDPE[ 18] and LDPE grafted diallyl bisphenol A ether [19][20], are another important compatibilizer. Graft migrates to the two-phase interface, and its polyethylene segment is compatible with PE in the * * * mixed component, and the other end is more compatible with PC, thus reducing the interfacial tension of the two phases, reducing the phase domain size, improving the interfacial adhesion and improving the compatibility of the * * * mixed system.
Two compatibilizers, polyhydroxybisphenol A ether and sodium salt of ethylene-methacrylic acid * * * (Surlyn 8660), were used to compatibilize HDPE/PC[2 1] at the same time. The compatilizer is designed for the extremely incompatible * * * mixed system, and the compatibility of the * * * mixed system is improved by adding two compatilizers, among which ethylene-methacrylic acid * * *.
3. Polypropylene (PP)*** mixed modified PC[22]
The compatibility between PC and PP is very poor, so it is necessary to add compatibilizer to improve the compatibility of * * * mixed system. The compatibilizer used is mainly the graft of PP, such as PP-g-MAH, PP-g-GMA, etc.
Adding MAH-g-PP to PC can significantly improve the processability and compatibility of * * * mixture. DSC, FT-IR and SEM studies show that there may be a reaction between PC and MAH-g-PP, resulting in PP-g-MAH, thus improving the compatibility of * * * mixture and the mechanical properties of the system. [23][24] In the mixed system of PC/PP/MAH-G-PP * *, when the content of PP is higher (more than 50%), the impact strength and bending strength of the * * * mixture decrease, and the impact strength and bending strength of the * * * mixture are greatly improved by adding 25-36% treated glass fiber. [25]
Grafting glycidyl methacrylate onto PP(GMA-g-PP)[26][27] can reduce the average phase domain size of PC/PP * * mixture from 20 microns to below 5 microns, and the glass transition temperature of PC phase in * * * mixture shifts to low temperature, which obviously improves the compatibility between them. At the same time, GMA-g-PP, as heterogeneous nucleating agent, increases the crystallization temperature of PP, thus obviously improving the mechanical properties of the composite system.
4.ABS*** mixed modified PC
PC/ABS is a kind of plastic alloy material with excellent properties, which has the advantages of low viscosity, good processing rheological properties, high thermal deformation temperature, excellent mechanical properties and low price. PC/ABS alloy is the most widely used and sold variety among PC alloys. The solubility parameters of PC are 39.8-41.0 (j/cm3)1/2, and ABS is 40.2-41.9 (j/cm3)1/2, which are close, so PC and ABS have certain compatibility. However, the compatibility between PC and ABS also depends on the butadiene content in ABS. Because PC and PB are difficult to be compatible, ABS with different butadiene content and ABS with different formulations depend on the compatibility of * * * mixture and the toughening effect of elastomer, and the properties of * * * mixture will be different. [28-30] Namhart [365438+.
The fluid of PC/ABS composite system is pseudoplastic. It is found in HAAKE torque rheometer [32] * * that the viscosity of the system decreases with the increase of shear rate, which shows that the addition of ABS improves the processability of PC. The PC/ABS composite system containing 20%ABS has higher crack propagation resistance than the PC/ABS composite system containing 40%ABS. Proper ABS content can effectively toughen PC/ABS system through cavitation and shear yield. [33]
Tang Song Superclass [34][35] adopts PE-g-MAH as compatibilizer, which not only improves the compatibility between PC and ABS, but also improves the compatibility between SAN and PB. The polarity of SAN in ABS is higher than that of PC, and its glass transition temperature is lower than that of PC. With the increase of ABS content, more SAN is mixed into PC, which reduces its glass transition temperature. The addition of ABS is beneficial to resist the shear stress caused by solvent, thus improving the stress cracking resistance of PC. After adding the antistatic agent alkylbenzene sulfonate, the surface resistivity and volume resistivity of the material are obviously reduced, which has obvious antistatic effect, and the antistatic effect is enhanced with the increase of ABS content. Because alkylbenzene sulfonate is a surfactant, proper addition can improve the fluidity of polymer, thus improving the compatibility of * * * mixture. When 1 part is added, the impact strength of the system is the best. When LLDPE-g-MAH was used as compatibilizer, the heat resistance, impact strength and tensile strength of PC/ABS system were improved. [36]
Balakrishnan[37][38] and others used MABS instead of ABS, a graft of MAH grafted by ABS. The PC/ABS simple binary * * * mixed system has coarse dispersion, while the PC/MABS*** mixed system with mabs compatibilization presents a layered dispersion structure, and its mechanical properties are greatly improved (Table 4).
Table 4. Notch impact strength (J/m) of PC and PC-ABS composites.
PC PC/ABS(75/25)PC/MABS(75/25)PC/MABS(90/ 10)ABS
126.4 86.2 882 280.7 320.3
American patent. No.302646 [39] uses a hydroxyalkyl acrylate grafted ABS(HEMA-g-ABS) as a compatibilizer, and the basic formula is: PC 62.5, HEMA-g-ABS 10, SAN 12.5, flame retardant 13, PTFE 66. Tjiong et al. [40] used the mixed system of MAH-g-PP and epoxy resin NPES-909 to compatibilize PC/ABS (70/30) * *, and the yield strength, tensile modulus and impact strength of the system containing NPES-909 compatibilizer were better than those of the non-compatibilizing system and the single compatibilizer MAH-g-PP compatibilizer system. Through DSC analysis, it was found that with the increase of NPES-909 content, the Tg of ABS and PC increased, and the δTg decreased from 19.7℃ to 12.7℃ (containing 2% NPES-909). It can be seen that the addition of double compatilizer greatly improves the compatibility between PC and ABS.
When the content of PC in PC/ABS composite system is high, PC surrounds SAN, and SAN contains grafted rubber phase. At the same time, the grafted rubber phase contains SAN particles as the stress concentration center, which induces a large number of crazing and shear bands, and the generation and development of a large number of crazing and shear bands consumes a lot of energy, thus significantly improving the impact resistance of the material; Rubber particles can inhibit the growth of crazing and make it stop without developing into destructive cracks. [4 1] With the increase of ABS content in * * * mixture, the content of rubber phase increases, and the material will become the bearing point of rubber phase under the action of external force, which will induce crazing and shear band. When the rubber phase content reaches a certain value, it can prevent cracking in time and improve the impact strength of the mixture; When the content of ABS further increases and exceeds 50%, the phase of * * * mixed system will be reversed, ABS will become continuous phase and PC will become dispersed phase, which is not conducive to the generation of shear band, but the impact strength of the material will decrease. [42][43]
5. Polyethylene terephthalate (PET)*** mixed modified PC.
PET is a continuous phase, and PC/PET is a completely incompatible system without accelerant. After adding accelerant, the compatibility was improved, and PC phase promoted the crystallization ability of PET. When PC is a continuous phase, PC/PET is a partially compatible system. Prolonging the mixing time will reduce the crystallization ability of PET and increase the disordered region, thus increasing the chain entanglement with PC, which is helpful to improve the compatibility of PC/PET system. At the same time, in the process of melt mixing, the functional groups on PC and PET segments react with each other, and the hydroxyl and carboxyl groups on the last chain of PC also react with the functional groups on PET segments, which increases their compatibility. [46] The PC/PET (50/50 wt%) system was transesterified for a long time to produce a random polymer of TCET. The existence of TCET reduces the interfacial tension of PC/PET and improves their compatibility. When the TCET content reaches 60 wt%, the PC/PET system has only one glass transition temperature, and the phase size and domain of the system are greatly reduced. [47] Twin screws melt * * * mixed PC/PET, and PET is dispersed in PC matrix. The smaller the dispersion degree of PET particles, the stronger the inhibition effect on crystallinity, that is, the greater the rotating speed of twin screw, the better the compatibility of PC/PET system. [48]
In order to increase the compatibility of PC/PET system, Liu Mingqing et al. [49] added 2-5 parts of elastomer to PC/PET system, and the elastomer particles dispersed between PC and PET particles, which became an obstacle to the growth of microcracks, effectively preventing the further growth of microcracks formed under stress, thus overcoming the shortcoming that the impact strength of PC/PET system decreased sharply due to the addition of PET, ensuring that the addition of PET improved the solvent resistance, stress cracking resistance and processability of the system. (Table 5) (including 80 PC, 05-25 PET 65438 and 2-5 elastomer)
Table 5. Performance comparison between PC and PC/PET/ elastomer
Impact strength (KJ/m2) Bending strength (MPa) Bending modulus (MPa) Tensile strength (MPa) Elongation at break (%) Thermal deformation temperature (℃)
PC 73 86 1700 50 84 126
PC/PET/ elastomer1108918705611515
Compatibilized PC/PET system with PE-g-MAH shows that PE-g-MAH, as heterogeneous nucleating agent, broadens the crystallization area of PET, while the crystallinity of PET increases and the crystallization integrity deteriorates, thus blurring the phase interface, improving the interphase osmotic pressure and improving the compatibility. [50]
The addition of a small amount of liquid crystal polymer (LCP) can accelerate the crystallization speed of PET and improve the mechanical properties of PC/PET composite system. Feng Jianmin et al. [5 1] added different LCPs to PC/PET system, and found that the crystallization rate of PET could be accelerated and the tensile strength of the system could be improved by about 30% only by introducing LCPs whose melting point was close to the temperature at which PET reached the maximum crystallization rate. Scott et al. [52] added Traidz LCP to PC/PET composite system and found that the modulus increased by 1GPa. SEM study shows that the addition of LCP makes the system form a large number of microfibers with large aspect ratio along the flow direction. Kwon et al. [53] found that the Tg of PC and PET was closer, which improved the compatibility of PC/PET composite system. When 10% LCP is added, the tensile strength of * * mixture is improved by 20-30%. Because microfibers are formed when 10% LCP is added, when the content exceeds,
6. Thermoplastic polyurethane elastomer (TPU)*** mixed modified PC
The rheological properties of PC/TPU*** mixture were studied by capillary rheometer. The viscosity of PC melt is not sensitive to shear rate, but sensitive to temperature. When the temperature reached 270-3 10℃, the viscosity of PC melt decreased to 1/4, and the addition of TPU greatly improved the fluidity of * * * mixture. When the temperature of TPU reaches 270-3 10℃, the fluidity of PC melt is improved. When a small amount of elastomer is added to PC/TPU, [55] elastomer is dispersed at the interface between PC and TPU, which improves the compatibility of PC/TPU system. When the ratio of PC/TPU/ elastomer is 80/20/ 15(wt%), the impact strength of the system is nearly three times higher than that of pure PC, and it is also much higher than that of pure PC/TPU system.
Kwon et al. [56] used two kinds of TPU: TPU-35 and TPU-53 (containing 35.5% and 53.4% rigid segments respectively). With the increase of quenching temperature of TPU content, the Tg of PC/TPU system decreased, regardless of TPU type. The degradation of TPU during quenching leads to the decrease of Tg and degradation temperature of PC/TPU-35 and PC/TPU-53.
7. Liquid crystal polymer (LCP)*** mixed modified PC
LCP is a highly oriented polymer and PC is a random polymer, both of which belong to partially compatible systems. The addition of LCP can effectively reduce the melt viscosity of PC, reduce the environmental sensitivity of internal stress, and improve the mechanical properties of * * * mixture in a certain range. [57] The molten PC/LCP has undergone ester exchange reaction, repolymerization reaction and degradation reaction. In the presence of initiator, the degradation reaction is accelerated, which changes the Tg and rheological behavior of the system and increases the compatibility between them. The viscosity of PC/LCP system is greatly reduced at 200-230℃, and the tensile strength of the system is the highest at 10wt% LCP. Scanning electron microscopy (SEM) shows that spherical liquid crystal polymers can be well dispersed in PC matrix, but the binding force between them is very weak. In the process of melt mixing, PC/LCP is in-situ composite, and LCP can be transformed into fibrous structure and oriented along the flow direction. Generally speaking, extrusion molding has more obvious orientation enhancement behavior than injection molding. [60][6 1]
Compatibilization of PC/LCP with epoxy resin and DDS. The addition of epoxy resin and DDS greatly reduced the interfacial tension of PC/LCP, promoted the strengthening of LCP and greatly improved the tensile strength of the system. [62] When PC-G-PET/60ph compatibilized PC/LCP, with the increase of compatibilizer content, the tensile strength, bending strength and elongation at break of * * * mixture increased, the phase interface became blurred, LCP became finer, and the aggregation of dispersed phase caused by long-term forced * * * mixing was relieved. [63]
8. Conclusion
Polycarbonate is one of the most widely used engineering plastics at present. Because of its excellent performance, it is widely used in places with high material requirements. However, polycarbonate has some disadvantages, such as difficulty in processing and high price. Many scientists and technicians have greatly improved the shortcomings of polycarbonate by mixing and modifying other polymers. As long as a suitable compatibilizer is added, two different polymers can be partially compatible and complement each other, thus greatly expanding the application field of polycarbonate.