Study on Polyamide 11/Halloysite Nanotubes Hybrid Poly (Lactic Acid) Composites and Reinforced and Toughened Melt-Blown Nonwovens

Author:Zhu Zuo Chao

Supervisor:han jian


Degree Year:2019





Melt-blown(MB)is an industrialized,one-step process for producing sub-micron/micron fibers.Melt-blown nonwovens(MBs)have been widely used in the fields of medical,adsorption and filtration materials due to their fluffy and porous structure,and extremely large specific surface area.Since the beginning of this century,with the tremendous development of bio-based and biodegradable melt-blown materials,environmental-friendly green MBs also have shown great potentials.Poly(lactic acid)(PLA)is the most widely studied bio-based/biodegradable polymer material.It has been widely studied and applied in many fields,such as packaging,disposable materials,medical and health materials.PLA MBs show great application prospects.However,due to the inherent mechanical brittleness and low thermal stability of PLA,the performance and applications of its final products are also limited.In order to obtain the enhanced and toughened PLA-based environment-friendly MBs,polyamide 11(PA11)and halloysite nanotubes(HNTs)are used as the reinforcing/toughening materials respectively,and the target reactive compatibilizer and surface modified nanofiller(Aminated HNTS(A-HNTs)and 3-Glycidoxypropyltrimethoxysilane modified HNTs(G-HNTs))are designed.The modified method has obtained the organic-inorganic hybrid composite masterbatch material for melt-blown nonwoven with good compatibility,improved thermal stability and excellent spinnability.The corresponding MBs with enhanced strength and toughening,combined with high filtration properties,are successfully prepared.The main conclusions of the each system are as follows:(1)PLA/PA11 blends and MBs system:PA11 and PLA are immiscible.PA11,as“spherical/ellipsoidal”phase,is dispersed in the PLA matrix;PLA exhibits different crystallization behaviors from the glassy and melt state,whose fastest isothermal crystallization temperatures are 120°C and 105°C,respectively.PA11 is beneficial for improving the thermal stability of PLA.With increasing the blending ratio of PA11,the viscosity of the blend systems is improved and the melt flowing index(MI)is decreased,but the rheological behavior of“shear-thinning”keeps unchanged.The suitable MB processing temperature for the blending system is 230-250℃;As regards the MBs system,the average diameter(dav)of the PLA MB fiber is about 3.07μm,PA11 decreases the MB spinnability of the PLA melt with the davv increasing to 4.31-6.56μm,together with more defects.The mechanical strength and toughness of the PLA/PA11 MBs are significantly improved compared with that of PLA.PLA/PA11 MBs have an increased pore diameter,gas permeability,reduced filtration resistance,and a slight decrease in filtration efficiency.(2)Dual-monomer grafted PLA-g-(St-co-GMA)compatibilized PLA/PA11 blends and MBs:The grafting ratio of GMA increases with the blending ratio of dual-monomer/initiator(St/GMA/DCP)and the thermal stability of PLA-g-(St-co-GMA)is similar to that of PLA.As the graft ratio increases,the crystallization rate decreases,but the melt viscosity increases significantly.Due to the compatibilizer of PLA-g-(St-co-GMA),the interfacial compatibility between PA11 and PLA is improved,but PA11 is still dispersed in PLA matrix with a spherical/ellipsoidal shape.The thermal stability of the compatibilized blends is further improved compared with that of the non-compatibilized system,and the melt viscosity is increased but the rheological tendency kept unchanged.The suitable MB processing temperature for PLA/PLA-g-(St-co-GMA)/PA11 blends is 235-250°C.The average diameter of the MB fiber is increased to 3.58-5.24μm,which is lower than that of the non-compatibilized system,and the spinnability is significantly improved.The mechanical strength and toughness of the MB material of the compatibilizing system is further improved compared with the non-compatibilized system.The compatibilized MBs have a reduced pore size and improved filtration performance,which is still lower than that of PLA MBs.(3)PLA/PLA-g-(St-co-GMA)/A-HNTs composites and MBs systems:A-HNTs are uniformly dispersed in PLA matrix with good compatibility,promoting the crystallization rate of PLA and effectively improving the thermal stability of PLA.The"shear-thinning"rheological behavior of the melt of the composite system is unchanged,and the viscosity increases with the blending ratio of PLA-g-(St-co-GMA)/A-HNTs.The suitable MB processing temperature is235-250°C;The MB spinnability of PLA/PLA-g-(St-co-GMA)/A-HNTs composite melt is excellent.The dav of the MB fibers is increased to 4.13-5.87μm,making the surface of PLA MB fibers become rough.Compared with the PLA MBs,the Young’s modulus and mechanical strength of composite MBs are higher than that of the PLA,but the elongations at peak stress are reduced.The pore size and the air permeability of the composite MBs are increased,while the filtration efficiency is higher than that of neat PLA.(4)PLA/PLA-g-(St-co-GMA)/(PA11/G-HNTs)hybrid composites and in-situ microfibrillar reinforced and toughened MBs systems:the dispersion morphology of PA11/G-HNTs in PLA matrix is similar to that of PLA/PLA-g-(St-co-GMA)/PA11 blends.Under the synergy of PA11and G-HNTs,the thermal stability of the hybrid composite system is further enhanced compared to that of PLA/PLA-g-(St-co-GMA)/PA11 and PLA/PLA-g-(St-co-GMA)/A-HNTs system.The“shear-thinning”rheological trend of the melt of the hybrid system keeps unchanged,and the viscosity increases with increasing the blending ratio.The suitable MB temperature of hybrid system is 240-255℃;PLA/PLA-g-(St-co-GMA)/(PA11/G-HNTs)hybrid composites presents excellent spinnability,the dav of hybrid MBs are increased to 3.94-5.69μm compared to that of PLA.PA11/G-HNTs(100/5)hybrid system can form a distinct in-situ microfibrillar structure(30-100 nm in diameter)in MB fibers,but this phenomenon is not obvious in the hybrid system of PA11/G-HNTs(100/10).The mechanical strength and toughness of the hybrid MBs are further improved compared to that of PLA/PLA-g-(St-co-GMA)/PA11 and PLA/PLA-g-(St-co-GMA)/A-HNTs systems.Compared with PLA/PLA-g-(St-co-GMA)/PA11 system,the pore size of hybrid MBs system is slightly increased,but the filtration resistance is lowered with improved filtration performance.The excellent high-efficiency and low-resistance performance is exhibited.