Study On The Topological Features And Properties Of LDHs/EAA/PP Composites

The nanocomposites are widely used day by day,in which the low cost and high performance of the two-dimensional(2D)nanomaterials/polymer composites is also one of the important developing directions.Layered double hydroxides(LDHs)has unique adjustable structure and special properties,and the LDHs matrix composites have superior properties.However,the compatibility problem between LDHs and nonpolar polymers limits the application of LDHs/polymer composites in some high-end fields.That is crucial to understand the relation between the properties and the structure evolution of LDHs/polymer composites and its formation mechanism.From construction of the orientation relation of LDHs lamellar structure,this work controls the LDHs lamellar structures by changing the ratio of Mg/Al via a hydrothermal method.The morphological structure of LDHs and its composites is investigated by combined with the first principle and the coarse grain molecular dynamics(CGMD)method.Moreover,several types of LDHs matrix composites,such as LDHs/ethylene-ethyl acrylate copolymer(EAA),EAA/polypropylene(PP),LDHs/PP,and LDHs/EAA/PP composites,are prepared by melting intercalation and exfoliated methods.The structure evolution,crystallization behaviors,and the thermal stability of as-prepared LDHs matrix composites are investigated in detail.The specific investigation and achievements are following:1.Through constructing the molecular models with different orientation relations of the metal ion in LDHs lamellas,the relations between the orientation relations of Mg2+ and the adsorbed properties of carbonate radical,Congo red(CR)ion,and acrylic ion(AA-)are investigated;The reaction activities of quantum chemistry are analyzed by quantum chemical parameters in detail,and the difference of the defect enhanced adsorption effect is found: The deform ability of molecules is improved and the reactivity is enhanced due to the smaller of the overall hardness(η)value of the defect structures in Mg/Al–LDHs;Mg2+and H defects are beneficial to narrow the energy gaps,which improves the HOMO level,decreases the electrophilic value(ω),and enhances the adsorption of nonpolar compounds;However,O defect(VOH)decreases the LUMO level,improves the value of ω,and enhances the electrophilicity and the chemical potential,in which the LUMO level drops greatly,and is more conducive to subjectobject interaction,accelerates the electrophilic reaction,and increases the adsorption of anions and polar compounds;The reaction activities of quantum chemistry are closely related to the defect orientation location of non-element missing in LDHs laminates,in which,the location of Mg Al2-OH defect in center greatly improves the local electronegativities and increase adsorption of anions and nonpolar compounds.2.By controlling the Mg/Al ratio,the Mg/Al ordered LDHs with different defect structures are prepared.The results of CR adsorption test verify defect enhanced adsorption mechanism: Mg Al2–LDHs and Mg3–LDHs have more Mg Al2-OH and Mg3-OH defects,resulting in the decrease of the order in LDHs lamellar and more VOH,thus affect the thermal stability and the ion exchanging ability of LDHs;Mg3–LDHs have the best defect enhanced adsorption ability for its abundant VOH and bulk defect,and its adsorption efficiency for CR is improved from 88 to 97 %.3.Based on the molecular structures of LDHs and EAA,the coarse-grained models of nanoplates(NNP)and block polymer Am Bn-DBCP are constructed,respectively: The microphase structures of Am Bn-DBCP are affected by NNP,at m:n = 5:5,the lamellar structure will change to random network structure,for NNP increasing the contact surface and bonding degree of two-phase;at m:n = 8:2,the cylindric capsule structure will change to spherical capsule structure for NNP preventing poor phase particles from congregation and two phase bonding;at m:n = 2:8,spherical capsule structure will change to cylindric capsule structure.4.According to the results of CGMD calculation and experimental,the conception,“shear texture” is creatively proposed,that is the preferred orientation of LDHs is in the AA phase of EAA matrix,and its formation mechanism is uncovered: The preferential orientated cylindrical capsule structure is more conducive to producing under shear;The mechanism of LDHs exfoliated in different EAA matrix is different,but the topological features are existed in similar characteristic,that is “shear texture”,which is related to the preferred distribution of LDHs in the EAA matrix;The shear textures are related to the interaction methods of LDHs and EAA,the melted flow index(MFI)and AA content of EAA,and the processing conditions.In addition,the selective dispersion of NNP particles has an important effect on the interfacial structures of the copolymer.The thermal stability of LDHs/EAA nanocomposites is greatly improved by controlling the molecular weight of EAA and the processing conditions to form a uniform orientation and ordered distribution of LDHs.CGMD and rheological tests confirm that the LDHs/EAA composites with MFI=20 g/10 min own a better solid-like behavior and network structure,which is favorable to improve the thermal stability of LDHs/EAA composites.Compared with pure EAA,the maximum heat degradation rate of LDHs/EAA composites is reduced by more than 50%.5.In LDHs/PP composites,the texture of LDHs is in the form of a multistage structure in the PP matrix,including the coagulation characteristics of a very small number of exfoliated LDHs lamellae(ELAC)and many parallel features of bulk LDHs lamellae(BLP),caused by the different diffusion coefficient of different LDHs contents,and with different quality contribution rate per unit LDHs to crystalline and thermal stability of LDHs/PP composites,in which 2%LDHs>6%LDHs;under the shear rate is0.1/ps,the diffusion velocity of 2%LDHs<6%LDHs.In EAA/PP composites,the β-i PP nucleation efficiency in EAA/PP increases slightly with increasing the value of MFI.The shear rate plays a crucial role on the formation of morphological structure of EAA/PP.Under the shear rate is 0.1-0.2/ps,the higher MFI EAA molecules disperse more evenly and form fine regular capsule texture in PP matrix.6.In LDHs/EAA/PP composites,Mg2Al-OH type LDHs(Mg2Al-LDHs)are always preferentially disperse in the phase state formed by EAA,mainly as encapsulated structures,which affects the thermal stability and crystallization behaviors of LDHs/EAA/PP composites.In a different action mode,the LDHs/PP–EAA composites prepared by blending LDHs/PP master batch are more easily to form local network space among encapsulated structures and has a higher thermal stability and stronger β-i PP crystalline ability.Additionally,by increasing an affinity between defect Mg Al2-LDHs and PP,the topological features of LDHs/EAA/PP composites will be changed,and it will form an interfacial texture of the encapsulated structure with LDHs as link(called “hard interfacial network texture”),which is different from the “soft interfacial network texture” with EE chain as link formed by ideal LDHs’(Mg Al2-LDHs)poor compatibility with PP.Two network textures have different effects on the crystallization and thermal stability of LDHs/EAA/PP composites.The “hard interfacial texture” has high thermal stability,and the peak temperature of the maximum degradation rate can be increased by more than 10 °C.Rheological studies confirm that two interfacial textures own better solid-like behavior,which can improve the thermal stability of LDHs/EAA/PP composites.