Post-functionalization of Rubbers for Nanocomposite Interfacial Regulation and Elastic Network Construction

Author:Peng Chuang

Supervisor:zhang xue quan


Degree Year:2019





Rubbers,as strategically important materials,have been widely used in tires,seals,and shock absorbers.To satisfy the practical applications,most of neat rubbers need to be reinforced due to their inherent weakness in strength and toughness.Various reinforcing nanofillers are usually used to toughen rubbers,among of which cellulose nanocrystals(CNCs)attracted much attention due to their excellent chemical and physical properties.On the other hand,bio-inspired energy-dissipating mechanisms have also been used to improve mechanical performance of neat rubbers.In this thesis,several reinforcement systems involving CNCs or energy-dissipating mechanisms in rubbers were discussed,and the abstract are listed as follows:1.Fabrication of homogeneous hydrophobic polymer/cellulose nanocrystals(CNCs)nanocomposites with high mechanical reinforcement is a tough issue owing to the poor interfacial interactions between the two components and the aggregation of CNCs in hydrophobic matrices.In this study,the polybutadiene(PB)nanocomposites reinforced With eotton-derived CNCs were prepared through a host-guest inclusion complex assisted approach.In the system the pendent guest adamantane moieties of PB reacted withβ-cyclodextrins(βCDs)to form inclusion complexes,which acted as competitive binding sites to the CNCs via hydrogen bonds,allowing the CNCs to disperse homogeneously in the matrix.Dynamic mechanical analysis and tensile testing studies of the nanocomposites revealed that the incorporation of CNCs into the polymer matrix significantly improved the mechanical properties.For the nanocomposites with 10wt%βCDs and 15wt%CNCs,the storage modulus,Young’s modulus,and tensile strength were enhanced by about an order of magnitude compared to neat PB.The increase in the PCD and/or CNC contents led to a shifting of the tan δ peak of the nanocomposite to higher temperatures,suggesting the presence of filler-polymer interactions.Moreover,scanning electron and polarized optical microscopy analyses revealed that in the matrix the individual CNCs aligned in parallel and longitudinal directions to form long and entangled assemblies.The reinforcement could be attributed to the filler-filler and filler-matrix interactions which consequently lead to the stress transfer between polymer and CNCs in the system.2.Interfacial interaction between matrix polymer and nanofiller greatly influences the mechanical properties of polymer nanocomposites.Herein,two kinds of functionalized polybutadienes containing carboxyl or hydroxyl groups,PB-COOH and PB-OH,were synthesized via thiol-ene reaction and utilized as matrices to investigate the reinforcing effect of CNCs.Homogeneous PB-COOH/CNC and PB-OH/CNC nanocomposites containing up to 30 wt%CNCs were successfully fabricated.The incorporation of CNCs into the polymers led to remarkably enhanced mechanical properties,while the reinforcing effect of CNCs was more pronounced for PB-COOH than that toward PB-OH.Transmission electron microscopy and theoretical modeling studies revealed that the mechanical enhancement is attributed to the formation of a CNC percolation network within the polymer matrix and the interfacial interaction between matrix and CNCs.Differential scanning calorimetry analysis demonstrated that the polymer-filler interaction in the PB-COOH nanocomposites was stronger than that in the PB-OH systems,which results in a larger amount of constrained polymers in the former system and consequently contributes an increase in storage modulus.Thus,the CNC-CNC and polymer-CNC reactions are both responsible to the mechanical enhancement of the resulting nanocomposites.3.Utilization of effective energy-dissipating mechanisms in rubbers has proved to be a versatile strategy to reinforce rubbers.However,introducing sacrificial bonds into unsaturated rubbers is still a challenge due to their limited reactivity.In this contribution,we demonstrated a facile approach for dual network construction in polyisoprene(PI)with reversible multiple hydrogen bonding.The approach is based on the design and synthesis of l,2,4-triazole-3?5-dione(TAD)derivates(TADnBu,TAD-TAD,and TAD-UPy)with moderate function groups and utilization of the“TAD-ene”click reaction.First,a model experiment of TADnBu and PI was conducted to check their reactivity.!H NMR of the resulting polymer revealed that TADnBu could rapidly and quantitatively graft onto PI backbone.Next,a series of PI dual network with different structure parameters of TAD-TAD and TAD-UPy section were prepared,and the correlation of their mechanical properties and the structure parameters was demonstrated through tensile test.Finally,the cyclic tensile test revealed the breakage and reformation of reversible multiple hydrogen bonding.Our work provides an avenue to introduce effective energy-dissipating mechanisms in rubbers.4.Fabrication of rubber/CNC nanocomposites with high mechanical reinforcement and good ductility is still challenge due to their intrinsic conflict.In this work,we demonstrated a PI/CNC nanocomposite with concurrent toughness and ductility by engineering dynamic Si-O bond in the interphase of PI and CNCs and constructing multiple sacrificial networks with hydrogen bonding and metal-ligand motifs.The dynamic nature of hydrogen bonding and metal-ligand motifs allows the nanocomposites with high stretchability through breakage and reformation of the sacrificial bonds.During external loading,the sacrificial bonds rupture prior to the fracture of the covalent network,thus dissipating energy efficiently to improve tensile modulus and strength of the material while maintaining the extensibility.The properties of the nanocomposites can be conveniently tuned through varying the structure parameters of the interphase and multiple sacrificial networks.Notably,the PI/CNC nanocomposites exhibited good reprocessability due to the dynamic nature of the linkage in the system.