| Wastewater from the papermaking industry is discharged after treatment,but the sludge production of papermaking wastewater is large and the paper sludge contains a large amount of organic matter.The traditional incineration process wastes the organic matter in the sludge and the disposal cost is relatively high.Stacking not only occupies an area,but also pollutes the land and reduces the utilization of land resources.This study uses paper mill sludge and high-density polyethylene as experimental materials,adding silane coupling agent and lubricant,and preparing paper mill sludge/high-density polyethylene wood-plastic composite by drying,blending,extrusion granulation and injection molding.Based on the analysis of the basic characteristics and composition of paper mill sludge,investigating the effect of contents of two different types of sludge(papermaking sludge and activated sludge),silane coupling agent addition amount,lubricant addition amount and mixed sludge ratio on the properties of wood-plastic composite materials.The performance of modified sludge and composites was characterized by FTIR,DSC,TG,SEM,digital image correlation,and mechanical properties testing.Through experimental research,the following conclusions are drawn:(1)The basic performance and composition analysis test results show that the papermaking sludge has higher fiber content and calcium content,about 40% and 20% respectively,while the activated sludge has less fiber content and calcium content of about 8% and 3.6%,but the content of inorganic substances such as N,S and Si is higher than that of papermaking sludge.The fibers in the papermaking sludge are fine and long,and are entangled with each other;the activated sludge is distributed in a granular form,and the fibers are short and the content is small.The pH of the papermaking sludge is about 8.36,and the pH of the activated sludge is about 7.72,which is weakly alkaline.(2)The addition of papermaking sludge and activated sludge to high density polyethylene can improve the mechanical properties of wood-plastic composites to varying degrees.For papermaking sludge,the mechanical strength of the composite reaches a maximum when the addition amount is 30%.The addition of papermaking sludge plays a nucleating role in the polymer system and promotes the crystallization of the matrix;dynamic storage modulus and complex viscosity show an increasing trend with the increase of papermaking sludge content;the strain distribution of the composite material is uniform and the stress is effectively transmitted,but the excess papermaking sludge causes the stress concentration phenomenon of the composite material;a certain amount of sludge can enhance the interfacial bonding ability of the composite material,and too much papermaking sludge will agglomerate in the plastic matrix and affect the strength of the composite material.Activated sludge has a similar pattern as a reinforcing material when it is combined with plastic.In this study,the optimal addition amount of activated sludge is 30%.(3)Adding a coupling agent to the paper mill sludge/high-density polyethylene composite system can improve the mechanical properties of the composite to varying degrees.With the addition of silane coupling agent KH550,the tensile strength,impact strength,flexural strength and flexural modulus of papermaking sludge composites and activated sludge composites all increased first and then decreased.The digital image correlation shows that the stress distribution of the composite with the appropriate amount of coupling agent is more uniform,the stress is better transmitted,and the macroscopic mechanical test results are in good agreement.The microscopic analysis of the electron micrograph also verified that the interface between the two phases of the composite is better with the proper amount of coupling agent,but the excess coupling agent easily forms a multi-molecular layer at the interface of the composite,which affects the performance of the composite.Comparative analysis shows that the composite material has the best performance when the amount of silane coupling agent added is 2% under the experimental conditions.(4)The proper amount of lubricant improves the mechanical properties of the composite,and when the amount of lubricant added is 3%,the mechanical strength of the papermaking sludge composite and the activated sludge composite reaches the experimental optimum.DSC results show that the addition of a proper amount of lubricant helps to improve the crystallinity of the composite;the digital image correlation shows that adding a proper amount of lubricant,the composite has a uniform strain distribution.When the content is more than 5%,the stress concentration of the composite material occurs,and the stress cannot be effectively transmitted.The electron micrograph of the microscopic interface shows that a small amount of lubricant can promote the interfacial compatibility between the sludge and the plastic matrix,no gap between the interfaces,the excess lubricant is easily caused to agglomerate,and the weakening of the interface leads to the peeling of the reinforcing phase.(5)The papermaking sludge and activated sludge are mixed into mixed sludge in different proportions,and added to high-density polyethylene,the mixed sludge composite material and the single sludge composite material are analyzed and compared,the addition of mixed sludge does not significantly improve the performance of the composite,while the single sludge can better improve the interface of the composite and improve the performance of the composite.(6)Comparing the mechanical properties of the two types of paper mill sludge composites,it is found that the performance of papermaking sludge composites is better than that of activated sludge composites.It is feasible to use paper mill sludge as a filler to form a composite material with thermoplastic polymer,the comprehensive performance of the composite material is affected by factors such as paper mill sludge types,paper sludge dosage,coupling agent addition amount and lubricant content. |
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