Preparation,Structure And Properties Of PBST Composite Fibers With Nanoparticles And Their Application Exploration

Aliphatic-aromatic copolymers have spurred much interest in recent years for their desirable biodegradability of aliphatic unit and good mechanical properties of aromatic unit.Poly（butylene succinate-co-terephthalate）（PBST）,one type of aliphatic-aromatic copolymers,has been intensively investigated on its preparation,biodegradability,thermal and mechanical properties for applications in fibers and yarns.However,unstable morphologies such as large spinning tension fluctuation,high end-breaking rate have been encountered in the manufacturing of PBST fibers,resulting in relatively poor mechanical properties and low productivity.Meanwhile,as a new emerging material,there are still many unknown knowledge on structure and properties of PBST,to some extent,limiting its further development and wide applications.Therefore,with the aim of solving the problems in real process and filling the blank of theory knowledge,studies on PBST polyester and fibers are essential both in fundamental researches and practical applications.On one hand,the unstable morphologies fundamentally should be ascribed to the complex structure transformation in processing and the relatively slow crystallization.As a result,in this thesis we first in situ record the structural evolution of PBST under different thermal and mechanical fields by the combination of synchrotron radiation X-ray technique and thermal-mechanical coupled equipment,which can provide theoretical guidance for designing the manufacturing and application of PBST;then we prepare the PBST nanocomposites and study the effects of concentration and shapes of nanoparticles（NPs）on the crystallization behavior,thermal and mechanical properties,and the formation of microstructure of polymer matrix,with objectives of improving the crystallization rate and properties on the premise of not damaging the original structure.On the other hand,as an environmentally friendly material,PBST should have more wide application fields rather than the only way on melt-spinning fibers.Considering the removal of dyes in wastewater,a matter of concern for the long-term development of industries and the sustainability of environment,we fabricate PBST nanofibrous membrane by means of popular electrospinning technique,functionalize the PBST fibers and explore the application of modified fibers in dye adsorption.The main contents and conclusions of this thesis are presented as follows.The structural evolution of PBST under different thermal-mechanical coupled fields was investigated mainly via synchrotron radiation X-ray wide-angle diffraction and small-angle scattering techniques.The results demonstrated that the development of structure was greatly dependent on the imposed heat and stress.Specifically,firstly,at any temperature,the crystal form of PBST was transformed during its uniaxial stretching,and original lamellae would be broken（i.e.strain-induced melting）at the early stage of the deformation.The basic reason of material yielding was the orientation of original lamellae along ±（40-50）o direction accompanying with their destruction.Secondly,the effect of temperature on structure changes of PBST in the process of uniaxial stretching was mainly reflected on the formation（i.e.strain-induced recrystallization）and morphologies of new lamellae.It was found that there were no new lamellae formed during further stretching at 25 oC,while new lamellae were formed at 50,100 and 150 oC,and the higher the temperature was,the earlier the lamellae appeared and the better the lamellar oriented.Thirdly,the structure changes of PBST under dynamic thermal and mechanical fields were more sensitive to strain and only relatively high temperature had prominent impact on it.PBST nanocomposites were prepared by the combination of the polymerization of monomers and the incorporation of the sphere silica（Si O₂）and fibrous attapulgite（ATP）NPs.The results showed that the dispersion of NPs,the lamellae structure,the crystallization behavior,thermal and mechanical properties of PBST were greatly influenced by the amount and shape of NPs.On one hand,regardless of the shapes of NPs,PBST nanocomposites with good distribution NPs could be fabricated;the crystal structure was not changed by the presence of NPs,while the long period of lamellar structure increased with the increasing NPs amount;meanwhile,the nucleation way of PBST was transformed by the addition of NPs from homogeneous nucleation to the domination of heterogeneous nucleation but coexistence with homogenous way,thus leading to more than half of the crystallization time shortened;the initial modulus and break strength of nanocomposites were enhanced due to the incorporation of NPs.On the other hand,when the amount of Si O₂ and ATP NPs in polymer matrix was same,the PBST/ATP nanocomposites had smaller long period of lamellar structure and larger breakage elongation than that of PBST/Si O₂ nanocomposites,which were closely related to the dispersion and morphologies of NPs.The structure and properties of PBST fibers with NPs prepared by melt-spun spinning were consistent with the above results.And also the effects of drawing temperatures during strectching on the structure and properties of PBST fibers were expored,indicating that temperatures higher than 100 oC were benifical to the improvement of breaking strength.The formation and development of hierarchical structure of PBST and its nanocomposites in the process of nonisothermal crystallization was explored by synchrotron radiation X-ray technique and polarized microscope.The results presented that the cooling temperature was responsible for the formation and evolution of every level in this hierarchical structure.Specifically,during the cooling process,crystals initially appeared at high temperature and the showing up of every crystal planes was asynchronous,accompanying with the decreasing lattice space.As the temperature decreased,periodically lamellar structure could be observed and the long period kept reducing due to the gradual and constant formation of crystals.With the further cooling temperature,small spherulites started to form and the size of them first gradually increased and then remained unchanged.Furthermore,the existence of NPs would not affect the formation of the hierarchical structure.However,compared with this process of pure PBST,NPs hindered the arrangement of molecules in an order way at the early stage of cooling process,resulting in the lower temperatures of crystals and lamellae formation;nevertheless,the final long period of lamellae and the sperulites formation temperature were almost unchanged due to the nucleation and crystallization enhancement of NPs.PBST nanofibrous membrane was fabricated via electrospinning technique for the first time after PBST was dissolved by the mixture of two different solvents,and the morphologies,structure and properties of nanofibrous membrane were investigated.Meanwhile,we prepared the water-insoluble cyclodextrin polymer（CDP）by the polymerization between cyclodextrin and citric acid.The CDP was used to functionalize the PBST nanofibers by in situ polymerization of CDP with presence of those fibers.And then the adsorption performance of modified PBST fibers was intensively explored.The results exhibited that the morphologies of PBST nanofibrous membrane could be adjusted by tuning the concentration of solution,the ratio of solvents,relative humidity and processing parameters.Owing to the coexistence of nano-scaled fibers and micro-scaled pores,the membranes were hydrophobic.Furthermore,it was observed that resultant PBST/CDP nanofibrous membranes were more efficient for the removal of methylene blue from aqueous solution when compared to pure CDP and pure PBST nanofibers.The adsorption performance of the composited nanofibrous membranes was also greatly influenced by the amount of CDP that dominated the surface area and surface morphologies of materials.Adsorption kinetics of PBST/CDP nanofibrous membrane fit well with pseudo-second order model and Langmuir isotherm model exhibited the maximum adsorption capacity of 90.9 mg/g.