| With the rapid development of modern printing technology and office printing and copying equipment,the amount of digital printing waste paper generated is rising rapidly.Paper for digital printing is usually produced using high quality chemical wood pulp.which is a high fiber quality secondary fiber.However,because digital printing methods and inks arc very different from traditional offset printing technology.digital printing waste paper does not take advantage of the traditional deinking manufacturing recycled paper industry,not only the problem of difficult deinking.but also the relatively low value-added products,digital printing waste paper technology development of efficient and high-value utilization of industry attention.In-depth study of the feasibility of the application of digital printing waste paper fibers in the field of biodegradable composites has long-term practical significance in the high-value utilization of waste paper resources and the development of environmentally friendly composites.In this paper.DPWF/PLA composites were prepared with digital printing waste paper fibers(DPWF)as reinforcement and polylactic acid(PLA)as matrix,and DPWF was modified with xylanase.cellulase.cationic polyacrylamide(CPAM)and silicon carbide nano(SiC).and the comprehensive properties of the composites such as mechanics,water absorption and microstructure were systematically studied.The effect of environmental pH on the hydrolytic degradation rate of PLA and its composites was investigated.and the following conclusions were drown:(1)With the increase of DPWF content.the interfacial bonding between fiber and matrix gradually deteriorated,and the mechanical strength was best at 20%fiber mass fraction,with tensile strength of 52.4 MPa.bending strength reaching 80.6 MPa.and bending modulus reaching 4856 MPa.the saturated water absorption and diffusion coeffieient.thermodynamic solubility,and permeability values of the composites all increased with the increase of fiber content.increased.The addition of fibers has a negative effect on the thermal stability of PLA.the increase of DPWF content leads to a decrease in the crystallization temperature of the composites,but has no effect on their melting temperature.(2)CPAM and nano-SiC significantly improved the mechanical strength of the composites.The tensile strength,bending strength and bending modulus of the composites modified with 1 wt%CPAM increased by 3.6%,5.4%and 29.4%,respectively,compared with those before the modification,and the tensile strength of the composites modified with 1.5 wt%nano-SiC increased by 7.1 MPa,and the bending strength and bending modulus increased by 10.9 MPa and 1289 MPa,respectively.The parameters related to the characterization of water absorption after modification showed different magnitudes of decrease,among which the CPAM-modified composites showed the largest decrease with a 4.64%reduction in saturation water absorption,but several of them still followed the Fickian diffusion mechanism in their water absorption behavior.DSC characterization results showed that the modification treatment of cellulase reduced the glass transition temperature of the composites;CPAM and nano-SiC increased the glass transition temperature of the composites,while the crystallinity decreased by 3.2%and 4.1%,respectively,compared with that before modification.(3)During the degradation process,the mass loss rate of both PLA and modified composites showed a gradual increase with the degradation time.the degradation rate and mass loss rate of PLA were significantly lower than those of DPWF/PLA composites,and the mass loss rate of unmodified composites reached 0.49%after 30 d of degradation in deionized water at pH=7.8,which was 0.36%higher than that of PLA.The mass loss rate of the modified composites was reduced,by 0.14%and 0.27%after modification with CPAM and nano-SiC,respectively.In addition,the hydrolytic degradation rate of both PLA and composites was related to the pH value of the hydrolysis environment,with the fastest degradation rate under alkaline conditions,followed by acidic conditions,and the slowest degradation rate of PLA and composites under neutral conditions.The number of pores and gaps increased significantly,and a large number of fibers were debonded from the matrix and exposed.The macroscopic morphology showed that PLA remained intact under different pH conditions,while the surface color of DPWF/PLA composite changed from gray to white under alkaline conditions.In this paper,the mechanical strength of DPWF/PLA composites was significantly improved by using CPAM and nano-SiC,and the effects of DPWF addition and pH on the degradation rate of PLA were investigated. |
PDF Full Text Request