| Cellulose nanofibrils (CNF) was used as strengthening phase to improve the properties of poly(lactic acid)(PLA). In order to improve the interfacial compatibility between hydrophilic cellulose nanofibrils and hydrophobic PLA, compatibilizer, silane coupling agent (MEMO) modified cellulose nanofibrils (M-CNF), biomineralized cellulose nanofibrils (CNF/HA) and silane coupling agent modified CNF/HA (M-CNF/HA) were blended with PLA. CNF were blended with PLA to produce CNF/PLA composite foams. The CNF induced the formation of HA on the walls of its inner pores. The properties of different composites were studied and the mechanism of interfacial cohesion was revealed.Rod-like CNF with a diameter of20nm in width dispersed in organic phase. The crystallinity of CNF improved, but the thermal stability decreased. The mechanical properties of CNF/PLA composites decreased because of poor interfacial cohesion. The hydrophilicity, degradability and light-shielding property of CNF/PLA composites improved because of CNF. The thermal stability of CNF/PLA composites decreased. FTIR indicated that hydrogen bond existed between-OH of CNF and C=O of PLA.Polyethylene glycol (PEG)1000was the best compatibilizer and improved the mechanical properties of CNF/PLA composites because of the decrease of Tg. Compared with PLA, the tensile strength and elongation of CNF/PEG/PLA composites improved28.2%and25.0%, respectively. The lower molecular weight of PEG was added, the faster the CNF/PEG/PLA composites degraded. The stronger hydrogen bond formed among-OH of CNF,-OH of PEG and C=O of PLA. The interfacial cohesion was improved by increase the adsorption layer and mechanical action.M-CNF keeps their integrity and rod-like morphology. The thermal stability and crystallinity of M-CNF was decreased. There are less hydroxyl groups in M-CNF than in CNF. The carbon-oxygen ratio of CNF and M-CNF was1.81and1.69, respectively. Si dispersed evenly in CNF matrix. The highest tensile strength of composites was obtained for PLA with1.0v/v%MEMO and1.0wt%CNF, the tensile strength and elongation improved42.3%and28.2%comparing with PLA. M-CNF can block some of the light through. M-CNF can disperse evenly in PLA matrix. The thermal stability of M-CNF/PLA composites was affected by M-CNF and modification degree of CNF.In order to give CNF more functionality, spherical Nano-hydroxyapatite (HA) particles of approximately30nm were synthesized on the surface of CNF after biomimetic mineralization. The carbon-oxygen ratio of CNF/HA composite was1.54; the calcium-phosphorus ratio of the composite was1.70. It is suggested that there are coordination and hydrogen bonding between CNF and HA. The thermal stability of CNF/HA composites was improved significantly in the temperature of380-600℃Coupling reaction occurred between CNF/HA and MEMO. And the peak of Ca2p shifted to higher binding energy. Through mechanical lock and interface adhesive, the tensile strength and elongation improved51.3%and29.3%comparing with PLA. The thermal stability of M-CNF/HA improved comparing with M-CNF. Also, the thermal stability of PLA can be improved by M-CNF/HA. M-CNF/HA and MEMO can block some of the light through. Ca, P, and Si dispersed evenly in PLA matrix. Hydrogen bond existed between-OH of M-CNF/HA and C=O of PLA.The Loeb and Sorirajan phase inversion/particle leaching method was used to prepare CNF/PLA composite foams. CNF in PLA can improve the mechanical properties, the surface roughness, and hydrophilicity. CNF also can induce the formation of HA, which have diameters ranging from200nm to2μm and a Ca/P ration of1.42. The spatial distribution of calcium and phosphorus elements was uniform. XRD, FTIR and mass increase analysis showed that the-OH of CNF can induce the formation and growth of HA. |
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