Study On Nano-reinforced Polyimine Composites

In this thesis,cellulose nanocrystals(CNCs)and layered double hydroxide(LDH)were used to improve the properties of polyimine(PIm).PIm is composed of reversible imine bonds,which can be altered by reversible exchange in the presence of environmental stimuli,such as pH,temperature and solvents,ets.It is of unique self-healing,recyclability,ductility and environmental friendliness.It has a good application prospect in the development of new intelligent polymer materials with advanced functions.Polymer nanocomposites are formed based on polymer and nanomaterials with special nano-effects to the polymer matrix,which can bring outstanding performance enhancement to the materials.Therefore,incorporation with nanomaterials are one of the ways to achieve enhanced properties of PIm.There are few researches on PIm-based nanocomposites.Among nanomaterials,chitosan,starch nanocrystals and CNCs of organic nanomaterials,two-dimensional inorganic nanomaterials in nanomaterials,including clay,graphene,boron nitride,disulfide and LDH.have high aspect ratios and mechanical performance.The fabrication of nanocomposites can significantly improve the mechanical properties of the polymer,and leads to the potential applications because of other functions of nanocomposites.In this paper,CNCs and LDH were used as nano-reinforcing materials for PIm nanocomposites.And the effects of nanocomposite on mechanical properties,thermal stability,light transmission,gas barrier properties and self-repairability of PIm1 were investigated.Based on the solvent replacement method for the preparation of CNCs,the CNCs/PIm1 nanocomposites were prepared by in-situ polymerization.The effects of CNCs content on the mechanical properties,thermal stability and light transmission of PIm1 nanocomposites were studied.The mechanical properties of m-CNCs/PIm1 nanocomposites prepared with CNCs silanization and CNCs/PIm1 nanocomposites were investigated.The compared results show that due to the high aspect ratio,crystallinity(82%)and dispersibility of CNCs,when the content of CNCs was 1 vol%,the tensile strength of PIm1 can be increased 24.9%,from 44.93 MPa to 56.11 MPa.The increase of tensile strength of PIm1 by 1 vol%m-CNCs was only 0.6%,which proved that the H-bonding interaction between CNCs and PIm1 is the key to the improvement of mechanical properties of nanocomposites.The complete dispersion of 1 vol%CNCs in PIm1 leaded to the increasing of the onset temperature of the second-step weight loss of PIm 1,which implies CNCs can increase the thermal stability of PIm1.When the CNCs content was 5 vol%,the transmittance was 0.64 mm-1,and the transmittance of all nanocomposties with various CNCs contents was less than 1.00 mm-1.The CNCs have little effect on the transparency of PIm1.The LDH-CIH formed by the reaction of p-aminophenylacetic acid and terephthalic acid was prepared by coprecipitation method.The solvent was brought into the interlayer monomer and LDH-CIH by immersing in the monomer-containing solvent.The LDH-CIH/PIm2 nanocomposite was prepared by in-situ polymerization of an aldehyde group.The effects of LDH-CIH contents on the mechanical properties,thermal stability,light transmittance,gas barrier properties and self-healing of PIm2 nanocomposites were investigated.The results of transmission electron microscopy and X-ray diffraction analysis show that a completely uniform structure was formed with LDH-CIH dispersed into PIm2 matrix when the content was in the range of 0-6 wt%.When the LDH-CIH content was 8 wt%,the characteristic peak of LDH-CIH appeared in the X-ray diffraction of the nanocomposite film,indicating that LDH-CIH was restacked in PIm2,and PIm2 chain intercalated into LDH-CIH with the layer distance increased.The results of tensile test showed that when the LDH-CIH content was 8 wt%,the tensile strength of PIm2 increased from 8.07 MPa to 14.67 MPa,with increase of 81.8%.The strong electrostatic attraction between LDH-CIH and PIm2 is a key reason for the great increase of mechanical properties.When the LDH-CIH content was 8 wt%,the LDH-CIH was restacked in the polymer,which resulted in a good gas barrier capability of the nanocomposites.When the LDH-CIH content was 2 wt%and 8 wt%,the transmittance of the nanocomposite film was 0.70 mm-1 and 1.01 mm-1,respectively,and the transmittance values were less than 1.11 mm-1 of pure PIm2.It implies that the addition of LDH-CIH can increase the transparency of PIm2.Thermal analysis of nanocomposites showed that the addition of LDH-CIH increased the initial temperature of the first-step weight loss and char of PIm2,resulting the enhanced thermal stability of the nanocomposites.The nanocomposite film with LDH-CIH content of 4 wt%maintained high mechanical properties after several times repeated self-repair.The above research results demonstrate that the hydrogen bonding between CNCs and PIml and the direct strong electrostatic attraction between LDH-CIH and PIm2 are the main reasons for the increase of tensile strength of nanocomposites.The uniform dispersion of CNCs and LDH-CIH enables nanocomposites to maintain high light transmission.The improvement in gas barrier properties,self-healing properties and thermal stability ofnanocomposites is mainly due to the cooperation of nanomaterials with the properties of the polymers themselves.The directly route of nanocomposites fabrication based on nanomaterials and polymers in this thesis provides a special way for the preparation and research of nanocomposites,and provides a research basis for the preparation of nanocomposites with high performance.