Mussel-Inspired Surface Chemistry For Interface Adhesion Improvements Of Low Dimensional Materials/Soy Protein-based Composites

Petroleum-based polymers take up to tens of hundreds of years to degrade,accompanying with significant injuries to our natural environment.Therefore,bio-based polymers have recently garnered more and more considerable research interests in terms of relieving the overdependence on petroleum resources.China as a large nation in wood products manufacture,processing and trade,the output and domestic demand of wood-based panels consistently ranked the first place in the world.However,the predominantly and widely used phenol-formaldehyde(PF)/urea-formaldehyde(UF)resins release formaldehyde throughout their entire life,which is detrimental to human's health.Throughout the 1930s,biodegradable soybean meal(SM)was used in plywood adhesives and other composites materials,as they are available in large scale,high protein content,low in cost,have no carcinogenic gas emission and convenient transportations,etc.However,there is a lack of study on the SM-based composites hybridizing of Zero-Dimensional nanoparticles,One-Dimensional nanotubes,or biomass fibers,as well as their surface chemical modification.We focus on the interfacial bonding,compatibilities and dispersion of the hybrid materials in different scales and dimensions(self-assembly diblock copolymer of poly(ethylene glycol)-block-polystyrene(PEG-b-PS),halloysite nanotubes(HNTs),microcrystalline cellulose(MCC)and soybean isolate protein fibers(SPFs)).The main results were summarized as follows:(1)Well-defined,core-shell structure of PEG-b-PS diblock copolymers were synthesized via a RAFT dispersion polymerization,which can uniformly dispersed into the soy protein isolate(SPI)matrix via the TEM observation;The tensile strength of the SPI/PEG-b-PS nanocomposite films were 7.06 MPa,improved by 85.3%,in company with the elongation at break increase.The simultaneously strengthening and toughening mechanisms achieved as:the hydrophobic PS core served as the hard-domains to strengthen mechanical properties,while,the hydrophilic PEG block conjunct with the SPI chains via hydrogen bonding,increasing bi-phase compatibility.Further,as the hydrophobic PS core surface-aggregation,the films' surface hydrophobicity was also elevated from 41.16° to 51.46°.(2)As the strength and toughness 1D materials were rarely prepared via self-assembly polymerization,the natural derived halloysite nanotubes were employed to strengthen the SM-based composites materials.The studies of mussel-inspired surface chemistry were as follows:a.Aqueous dopamine can bond to alumina/silica at the tube and self-polymerized to form a thin,surface-adherent polydopamine(PDA)ad-layer,which can generate second reaction to anchor the silane agent(KH560)to the PDHNTs surface confirmed by the X-ray photoelectron spectroscopy(XPS),Fourier transform infrared spectroscopy(FTIR),thermogravimetric analysis(TGA),and Transmission electron microscopy(TEM)etc.The surface modification of the PDA coating and silane grafting was successfully carried out.The SPI chains were supposed to penetrate and entangle to the PDHNTs-O nanotubes(inner diameter at 19-32 nm).The tensile strength of the PDHNTs-O/SPI nanocomposite films was reached to 8.73 MPa,and its moisture absorption was decreased by 47.1%.b,"One-step" of ?-poly-L-lysine(?-PL)/dopamine were co-deposited onto HNTs to engineer a multi-network of HNT/SPI bionanocomposite films.The XPS,UV-vis,FTIR,TEM analysis showed that:the ?-PL with abundant cationic amine groups could prevent the overoxidation of dopamine on HNT surfaces,maintaining sufficient free catechol groups for highly active reactions and be more compatible with peptides.The tensile strength of the nanocomposite film(DLHNTs0.5/SPI)reached to 8.25 MPa,and the Young's modulus was improved by 166.4%.(3)The natural-derived microcrystalline celluloses(MCC)and SPFs are ideal materials for the fully-renewable soybean meal-based composites materials.A novel and facile mussel-inspired surface modification approach and the concept of "self-reinforced" in polymer industry were applied in our study,the results showed as follows:a.The PDA layer was successfully coated onto the MCC surface via a simple dip-coating method as confirmed via XPS,FTIR,Solid state 13C Nuclear Magnetic Resonance(13C NMR)and atomic force microscopy(AFM),etc.As expected,favorable interfacial adhesion enhanced the mechanical properties by 82.3%of the resultant composites,as well its water absorption reduced by 31.3%.b.The "self-gluing" concept of the SPFs network skeleton binding with the SM matrix in the aid of 1,2,3-propanetriol-diglycidyl-ether(PTGE)crosslinking.The FTIR,XRD,Differential scanning calorimetry(DSC)and FE-SEM analysis demonstrated the fine SPFs-to-SM interfacial compatibility and improved biphase bonding.The wet shear strength of the resultant plywood reached its highest of 1.12 MPa(>0.7 MPa,GB/T 9846-2015).