Preparation And Properties Of Lignin-based Light-driven Shape Memory Polymers

Lignin is the main organic component of plants and widely exists in all kinds of plants.As a by-product of pulp and paper industry and bio-refining industry,very little lignin is processed into industrial products,and most of the rest is used as fuel recovery energy,which causes a great waste of resources.Degradation of lignin into small aromatic hydrocarbons is one of the most valuable high-value directions,but it is still in the laboratory stage at present.Therefore,at present,the more common idea is applied to composite materials to replace similar materials and blend with other materials to reduce the cost,but this way cannot reflect the advantages of lignin itself.If the high value-added application of lignin is further expanded,it is necessary to combine the advantages of lignin itself and find other effective ways to really accelerate the high value-added process of lignin.Therefore,this paper effectively combined the photothermal conversion characteristics of lignin and the benzene ring structure advantages,and applied lignin to the field of shape memory polymer（SMP）,and developed a series of lignin-based light-driven SMPs.In this paper,unmodified lignin（EL）was directly used to prepare lignin-based light-driven shape memory polymer（ELEP）with extremely high lignin content.Based on esterification,high strength lignin-based light-driven shape memory polymer（ELID）was prepared.Based on the dynamic covalent bond theory,the work in Chapter 3 further enpowers the recycling capability of lignin-based light-driven SMPs.The specific work and research contents are as follows:（1）Since the biomass refining industry from the EL as the hard end,polyethylene glycol as the soft end,epoxy soybean oil as the curing agent,through the ring-opening reaction of epoxy groups with lignin and polyethylene glycol hydroxyl,design and preparation of a high wood quality,three-dimensional network structure of the light-driven SMPs（ELEP）.The ELEP reaction was characterized by Fourier transform infrared spectroscopy（FTIR）and gel content experiment.The properties of ELEP were tested by electronic universal testing machine,TG,DSC,DMA,photothermal experiment and shape memory experiment.The tensile strength,thermodynamic properties,photothermal properties and shape memory properties of ELEP with different proportions of lignin content were investigated.The results showed that the mass of lignin was up to 60wt%,and when the content of lignin was 55wt%,the tensile strength could reach 30.8 MPa and the elongation at break could reach 24.8%,which showed good mechanical properties.In the light-driven shape memory test,the shape fixing rate and shape recovery rate of ELEP50 were tested for 8 cycles.Under the irradiation of 2 sunlight（2000W/m²）,ELEP50 could be restored to its initial shape in 20 s,showing good light-driven shape memory performance.（2）In order to further improve the mechanical properties of lignin-based light-driven SMPs,a kind of lignin-based polyester polymer（ELID）was developed by EL.The ELEP reaction was characterized by Fourier transform infrared spectroscopy（FTIR）and gel content experiment.The properties of ELID were tested by electronic universal testing machine,TG,DSC,DMA,photothermal experiment and shape memory experiment.The tensile strength,thermodynamic properties,photothermal properties and shape memory properties of El EP with different proportions of lignin content were investigated.The maximum tensile strength can reach 46.9MPa（ELID30）,which is 52%higher than the previous work.The maximum elongation at break can reach 93.7%（ELID20）,and the fracture energy can reach 10.75 J·cm^-3.The mechanical properties are further improved in this work.Both R_f and R_r of ELID reached the maximum value of 98.7%and 97.4%respectively in ELID30,and completed photo-shaped memory in 60s.Moreover,they provided a wider glass transition temperature range（21.2℃-157.3℃）,which could be used as heat-sensitive warning films.（3）The recyclablelignin-based light-driven SMPs（EELD）with dynamic reversible structure was prepared by epoxide modification of EL.The EELD reaction was characterized by Fourier transform infrared spectroscopy（FTIR）and gel content experiment.The properties of EELD were tested by electronic universal testing machine,rotating rheometer,TG,DSC,DMA,cycle experiment and shape memory experiment.The tensile strength,thermodynamic properties,cycle properties and shape memory properties of EELD with different proportions of lignin content were investigated.Compared with the work in Chapter 3,the tensile property of lignin-based light-driven SMPs（45.2Mpa）was basically maintained,and the fracture energy of EELD31 could reach 11.8J·cm^-3,higher than the previous work,and the fracture energy of EELD21 could reach 15.7J·cm^-3.That’s a 46%increase over the last job.In this work,the IR spectra and mechanical properties of EELD before and after cycling were further tested.The results show that the structure and properties of EELD after cycling are relatively stable.Through stress relaxation experiments,the activation energy of EELD31 is calculated to be 142.2KJ/mol,which can be stress relaxed and has a circular flow.In addition,although EELD loses a little thermal stability compared to the previous work,lower light intensity is needed to achieve the condition temperature that triggers shape memory.The R_fand R_rof EELD31 are 99.0%and 97.9%,which are further improved compared with the previous chapter.