| Polymers have shown great application potential in the fields of packaging,medical treatment,construction,automobiles and disposable goods due to their low cost,light weight,good processing performance,and great stability.However,most polymers must be disposed of by means of landfill and incineration after use because of the slow degradation,which in turn will cause secondary pollution to the environment.Biodegradable polymers are considered to be able to solve the “white pollution” problem caused by refractory polymers,and are also a strategic choice to achieve sustainable economic development.The “plastic restriction order” was officially implemented on January 1,2021.The agency predicts that the demand for biodegradable polymers will be close to 2 million tons,with a 45-fold growth space.Among them,the demand in the fields of takeaway,express delivery,packaging plastic bags and agricultural film can reach 220,000,920,000,440,000 and 400,000 tons,respectively,for a total of 1.98 million tons,and the market value of biodegradable polymers exceeds 30 billion yuan.Therefore,the development and application of biodegradable polymers has become a research hotspot at this stage.Among the developed biodegradable polymers,Poly(butylene succinate)(PBS)as a typical semi-crystalline aliphatic polyester,with good toughness,thermal stability and chemical stability,has broad applications prospect in disposable products such as: food packaging,agricultural mulch,etc..However,the lower mechanical strength and modulus limit the use of PBS as injection molding and compression molding products;the lower melt strength and melt stability of aliphatic polyester also limits the blow molding process of PBS.Therefore,in order to broaden the application of PBS,this work focuses on the two crucial points of PBS mechanical enhancement and PBS melt strength enhancement modification.This study aims at the key issues such as formulation design,morphology control,and compatibility regulation in blending modification to control the disperse phase morphology and the interaction between the matrix and the dispersion phase.Then we have intensively studied the preparation,structure-properties relationship and and the processing and forming mechanism of PBS enhancement material.The main research contents and results are listed below:(1)For polymer/polymer reinforced blends,the dispersion state of the dispersed phase has a great influence on the properties of the blends.We studied the enhancement effect of the diameter of the dispersion phase on the PBS matrix by adjusting the shear rate during blending processing,without adding any compatibilizer and without changing the interaction force between the two phases.In this work,PBS/Poly(ethylene glycol-co-cyclohexane-1,4-dimethanol terephthalate)and PBS/Polylactic acid two series blends with a dispersion phase contents of 10,20,and 30 wt% were prepared at four screw speeds for the comparative study.The study found that the PBS/PLA blend has smaller dispersion diameter at a lower shear rate,but the diameter of PLA have no obvious decrease with the increase of the screw speed.However,for PBS/PETG blends,when the added content of PETG is 20 wt%,the diameter of PETG phase is larger than PLA under low screw speed,but with the increase of screw speed the diameter of the dispersion phase decreases significantly.Meanwhile,the enhancement effect of PBS/PETG is better than that of PBS/PLA.The yield strength of the blends increased from 26.2 MPa to 33.4 MPa with the amplitude of 27.5%.The influence of the dispersion phase diameter on the other physical properties of the blends also was analyzed,including crystallization properties,heat distortion temperature,thermal stability,etc..Through this high-speed shearing method,we have obtained PBS/PETG blends with excellent performance.This work also provides a new idea that we could prepare high-performance polymer/polymer reinforced blends with smaller dispersed phase by high-speed extrusion.(2)In the polymer/polymer reinforcement system,the phase morphology of the dispersion phase also has a great affect on the reinforcement.There are a number of researchers convert the spherical dispersed phase into polymer fibers for better enhancement by in-situ fibrillation process.However,in the previous works,there are few studies on further regulating the in-situ fiber morphology by adjusting the diameter of the initial dispersion phase.Then the prepared PBS/PETG blends were subjected to a ‘‘melt extrusion-uniaxial cold stretching” process to convert the dispersion phase into fibrillar structure,and the diameter change and property enhancement of PBS/PETG blends were further studied.Firstly,the influence of temperature on the melt extrusion-uniaxial process of the PBS/PETG blends was studied,and then the optimal deformation temperature(110,200,200,190 ℃)was setted for processing different initial dispersion phase.The study found that the diameters of the PETG was changed from 2.25,1.29,1.11,0.89 μm to 1.13,0.64,0.50,0.38 μm,respectively.And the the diameter of PETG before and after the in-situ fiberization were both around 2.1,indicating that the initial diameter size determines the final fiber diameter during the in-situ fiber formation process.This work enriches the deformation process under the shear of dispersed phase and the fiber forming mechanism in in-situ fibrillation process,and provides a new idea for in-situ fiber preparation of high-performance polymer/polymer composites.(3)Melt strength of polymer is a very important physical parameter in tensile deformation,and it is also a key factor to determine the polymer materials whether could be molded smoothly during blow process.To enhance the melt strength of PBS,cellulose acetate butyrate ester(CAB)was introduced to improve the intermolecular interaction force of PBS.Hydroxyl groups in CAB could form intermolecular hydrogen bonds with carbonyl groups in PBS,thus affecting the physical properties of the final blend materials.CABs with different hydroxyl contents were added into PBS.CAB was used as the “bridge” to improve the interaction force between PBS molecular chains,so as to achieve the purpose of melt-strength enhancement.The effect of CABs with different hydroxyl content on the melt strength of PBS was studied.IR spectra showed that the hydroxyl group in CAB could form hydrogen bond with the carbonyl group in PBS,and the content of hydrogen bond would affect the interaction force between PBS and CAB molecules,thus affecting the physical properties of the final blend material.In addition,the compatibility between CABs with different hydroxyl content and PBS was analyzed through morphology observation,the change of PBS glass transition temperature and crystallization temperature.The results showed that the higher the hydroxyl content in CABs,the better enhancement of PBS melt strength,and even showed obvious tensile hardening behavior of PBS/CABs blends.However,the addition of CAB would lead to the decline of PBS crystallization performance,which would lead to the decline of PBS mechanical properties.In our work,blends with strong interaction forces with the matrix are selected as the “bridge” between the molecular chains of the matrix to improve the melt strength of the matrix,and provide new ideas and insights for the melt-strength enhancement and modification of aliphatic polyester.(4)With the introduction and implementation of “plastic limit order”,it is urgent to prepare biodegradable blown films with excellent performance to replace the existing non-degradable polymer films.The biggest restraint for PBS to blowing molding is the low melt strength,then it is difficult to form effective intermolecular interaction force in the process of blow molding to maintain the stability of bubble,resulting in gourd-shaped bubble and even bubble rupture.On the basis of studying the influence of CABs on the melt strength of PBS,we chose four kinds of CABs to study the blowing molding process of PBS/CAB blends and the rheology in the blowing process.The apparent elongation viscosity in the blowing process was fully analyzed.And the relationship between the apparent elongation viscosity and the formability and the morphology of the film bubble was established in the PBS/CAB bolwing process.These results provided a reference for the film blowing performance of aliphatic polyester.At the same time,the physical properties of PBS/CAB blend films were compared with those of commercial PE films and PBAT films.The results showed that the introduction of CAB was beneficial to the stability of PBS bubble,and PBS/CAB blown film could be successfully prepared.The maximum inflation ratio could reach 4.61,which meets the actual production requirements(inflation ratio is 3).In addition,the yield strength,Young’s modulus and tear strength of the blown film also could meet the requirements of commercial shopping bags.Our work provides a new direction for the development and application of completely biodegradable polymer film. |
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