Effect And Control Of Biomimetic Compatibilization Of Moso Bamboo Flour/High-density Polyethylene Interface By Using Polydopamine

Moso bamboo flour/high-density polyethylene(MBF/HDPE)composites show a bright future in the engineering field due to their advantages such as rich raw materials and being eco-friendly;however,the properties of MBF and HDPE are quite different,making their compatibility not ideal.In this paper,based on the of polydopamine(PDA)technology inspired by mussel super adhesive proteins,a kind of biomimetic modification method with mild conditions and being environment-friendly was proposed,which was aimed to serve the improvement of bamboo plastic interfacial bonding,and open up new ideas for the development of high-performance composites and the reasonable utilization of forest resources.The main conclusions and innovation points are as follows:1.A dopamine(DA)solution dipping process was established for in situ constructing PDA functional coating on MBF surface,and the biomimetic compatibilization of MBF and HDPE was realized;the typical compatibilization effect was revealed,and the control strategies were explored from the views of modifier,reaction condition,and additive.Besides,the idea of fractal geometry was introduced into the evaluation system;according to the fractal dimension(D_f)for granularity,surface morphology and structure of MBF,and the D_ffor internal pore and fracture surface morphology of composites,the statistical self-similar nature of these properties was revealed,and the modification effect of PDA modification was proved.Furthermore,for the typical thermal behaviors of MBF and composites,the changes in dynamic parameters and thermodynamic indexes were concerned,which laid a foundation for understanding the internal influence of PDA.2.PDA optimized the surface properties of MBF and makes many contributions for the compatibilization of MBF and HDPE from physical and chemical aspects.Taking the MBF treated with1 g·L^-1DA solution for 24 h at room temperature as an example(Tris solution as reaction medium and O₂as oxidant),the surface morphology of this modified MBF is more elaborate than that of untreated group(UNT),leading to the higher surface roughness and a 14.18%increase in specific surface area,and elevating the D_ffor surface morphology and pore structure by 3.85%and 4.14%,respectively,which was conducive to the infiltration and interlock between MBF and HDPE;meanwhile,the free hydroxyl concentration of the modified MBF increased by 23.22%,indicating a higher reaction activity,which served as an important premise for inducing the super adhesion of PDA to realize the reinforcement of bamboo plastic interface.Under the above effects,the wettability of the modified MBF became better;to water and diiomethane,its interfacial tension decreased by 5.03%and 33.60%,respectively,and the adhesion work increased by 9.59%and 3.71%,respectively,while its surface free energy increased by 7.82%.3.PDA elevated the interfacial bonding degree between MBF and HDPE,and realized the strengthening,stiffening and toughening of composites.Compared with UNT,composites prepared with the above-mentioned modified MBF showed a pore structure that was simpler and more regular;its D_fdecreased by 1.73%,and the specific volume,specific surface area,and average pore diameter decreased by 35.90%,27.46%,and 11.54%,respectively.The enhancement of interfacial adhesion inhibited the water absorption behavior;the weight gain and thickness expansion after 720 h water absorption of the PDA-modified composites decreased by 54.23%and 36.75%respectively,and the water diffusion coefficient decreased by 6.74%.In terms of mechanical properties,the flexural strength,flexural modulus,tensile strength,tensile modulus,and impact strength of the PDA-modified composites increased by 26.53%,30.09%,31.66%,37.68%and 18.33%,respectively.When the modified composites cracked,the stronger interaction between components resulted in the intricate fracture surface morphology,which increased D_fby 1.19%.4.PDA promoted the interaction between MBF and HDPE,which inhibited the thermal behaviors of molecular chains,and improved the thermal stability of composites.Compared with UNT,the 5%loss temperature and half-life of storage modulus(in the glass transition)of the aforementioned PDA-modified composites prolonged by 3.10°C and 2.60%,respectively,while its temperature of deflection under load(HDT)and melting onset temperature increased by 7.60°C and 0.32°C,respectively,and the peak temperature of crystallization exothermic rate decreased by 0.41°C.At the melt state,its equilibrium torque increased by 4.54%,and the flow rate decreased by 18.66%.During pyrolysis,its 5%weight loss temperature and half-life of weight increased by 16.60°C and 0.24%,respectively,and the activation energy and Gibbs free energy increased by 15.59%and 1.22%,respectively.5.The PDA modification was performed by using DA and its analogues catechol(CT)and dopa(LD)as monomers.For the interfacial bonding and mechanical properties,DA group composites were generally better,and this group also showed the lower weight gain after water absorption and higher HDT;however,CT group produced the greater inhibition on glass transition,and its half-life of storage modulus was 2.72%longer than that of UNT;on the other hand,LD group had the stronger pyrolysis resistance,and its activation energy increased by 19.00%.6.During the DA treatment of MBF,the composition of reaction medium(Tris,Na OH,NH₄OH,K₂HPO₄,Na HCO₃)and the oxidant(O₂,Cu SO₄,Na IO₄,(NH₄)₂S₂O₈,Fe Cl₃)affected the modification result.From the point of view of improving the interfacial adhesion,mechanical performance,and water resistance of composites,the more suitable medium and oxidant were Tris solution and O₂,respectively.In terms of improving thermal properties,among different mediums,the HDT of Tris group was higher,the glass transition intensity of Tris group and Na HCO₃group was weaker,and the pyrolysis resistance of NH₄OH group was stronger;among different oxidants,the HDT of Na IO₄group was higher,and its resistance to pyrolysis was also generally better,while the stability of storage modulus of O₂group and Na IO₄group was better.7.When DA was co-deposit with surfactant(CTAB,SDS,SDBS,PVP)or silane(APTES,GPTMS,MAPTMS,MPTMS)to coat MBF,the composites will be given new characteristics,which can be used to tailor some modification effect.For example,some anionic surfactants can promote the toughness or pyrolysis resistance of composites obviously;the impact strength of SDS group increased by 43.73%,while the pyrolysis activation energy of SDBS group increased by 34.28%.When silane was involved in the modification,composites can be further strengthened and stiffened;the flexural strength and modulus of MPTMS group increased by 41.45%and 31.47%,respectively,the 5%loss temperature and half-life for the storage modulus of GPTMS group were 12.30°C and 7.08%greater than those of UNT,respectively,and the HDT of APTES group increased by 9.60°C.8.The low-cost PDA simulant prepared by combining CT and polyamine(DETA,TETA,TEPA)played a role in improving the performance of composites.The TEPA-CT group showed more ideal modification effect in many aspects;compared to UNT,its flexural and impact strength increased by22.90%and 29.78%,respectively,its weight gain after 24 h and 72 h water absorption decreased by50.06%and 46.54%respectively,and its HDT increased by 7.30°C.However,TETA-CT group gave an obvious promotion on pyrolysis resistance;its 5%weight loss temperature was 24.32°C higher than that of UNT,and the increase of activation energy and Gibbs free energy were 11.74%and 8.23%,respectively.This attempt provided an opportunity for the practical application of PDA technology.