Study On The Property Tuning And Application Of Pulp Fiber Porous Foam Materials

With the increasingly stringent national environmental policy act,the use of non-biodegradable plastic products will be increasingly restricted.Traditional foam accounts for an important part of the total production of plastics,with excellent properties such as low density,high specific strength,good insulation properties and energy absorption properties,and is widely used in various fields.However,it has caused serious pollution to our environment due to the non-renewable raw materials used to produce plastic foam and the inadequate recycling policy.Foam materials with a three-dimensional porous structure prepared from pulp fibers feature low density,thermal insulation,and sound insulation,which is a green,degradable,renewable,and biocompatible biomass-based material.Considering the disadvantages of pulp fiber foam such as low mechanical properties,poor water resistance,and flammability,the utilization of foam is still limited.Therefore,it is important to develop new technologies for the preparation of pulp fiber foam materials to improve their properties.In this study,a lightweight and biodegradable pulp foam with a stable structure were prepared using foaming technology,and the properties and environmental impact of the material were evaluated.The flexibility and hydrophobicity of the foams were achieved by using chemical cross-linking and vapor deposition.In addition,the flame retardant properties of the materials were achieved by two different methods（organic-inorganic hybridization and biomimetic cross-linking）.Theoretical support and novel concepts are provided for the preparation,property tuning,and application of pulp fiber foam materials.Lightweight and biodegradable pulp foam material with a stable structure was prepared by foaming technology using bleached softwood pulp.The effects of refining pretreatment,PAE wet strength agent addition,and foaming process on the stability,structure,and mechanical strength of the foam were investigated.The biodegradability,production costs,and carbon emissions of the foam material were evaluated.It was found that refining pretreatment and PAE addition can improve the stability of wet foams.It can also promote inter-fiber bonding and improve the mechanical strength and water stability of the foams.The compressive modulus and stress depend extensively on the density of the material,which shows a power law.In addition,the foam material exhibits good biodegradability,with a degradation rate of 93%in only 85 days under outdoor composting conditions.The product not only can be used as disposable products but also can be recycled as a reusable fiber.It has obvious advantages over traditional foam in terms of cost and carbon emission and is expected to replace plastic foam in the field of cushioning packaging and insulation.Flexible and hydrophobic pulp fiber foam was prepared by foaming technology,in which the fibers were crosslinked by glyoxal and modified with MTMs by the CVD method.The changes in physicochemical properties during the preparation of the foams were investigated,and the potential of the materials for cushioning packaging and oil-water separation applications was studied.The results showed that two aldehyde groups of glyoxal reacted with hydroxyl groups on the surface of pulp fiber to form acetal bonds under an acidic medium and at a temperature of 90℃.The mechanical resilience of the foams was significantly improved,with plastic deformation rates of 19%and 14%after 10 cycles of compression for CPF and MCPF foams,respectively,indicating that the material can be used for the application of cushioning packaging.The water contact angle of the foams up to 145.9°was achieved after the vapor deposition of MTMs.Meanwhile,the density and porosity of the foams showed slight variations,with the densities of PF,CPF,and MCPF foams being 15.2 mg/cm³,15.8 mg/cm³,and 16.5 mg/cm³,and the porosity being 98.99%,98.95%,and 98.90%,respectively.The MCPF foam exhibited excellent oil adsorption capacity（between 30.0 g/g and 46.6 g/g）and was able to maintain 83.8%absorption capacity after 10 cycles of recycling by extrusion.The analysis of adsorption kinetic parameters showed that the adsorption process of the foam would be changed from Pseudo-second to Pseudo-first order with the increase in temperature.In addition,the foam features excellent thermal stability,which is a significant advantage compared to polymer-based foam materials.Foam material with flame retardant,thermal insulation,and acoustic insulation properties was prepared by foaming technique using bleached softwood pulp and hollow glass microspheres（HGMs）.The changes in physicochemical properties during the foam fabrication process were investigated.The results show that the stability of the wet foam was improved and the fiber distribution was more homogeneous after the addition of HGMs.The flame retardant properties of the foam were significantly improved.compared with HMF_4/0 foam,the PHRR and THR of HMF_4/4 foam were decreased by 44.9%and46.5%,respectively.Moreover,the CO₂ production and effective heat of combustion（EHC）were decreased by 52.9%and 41.0%,respectively,and the oxygen index up to 26.2%.Meanwhile,the foam showed good thermal insulation properties with thermal conductivity of 48.2 m W/m K,and excellent acoustic absorption with a noise reduction coefficient（NRC）value of 0.41.The mechanical properties of the foam were significantly improved,with a specific compression modulus of 6.06 MPa·cm³/g.The water-resistance of the foam can be improved by hydrophobic modification.This product can not only be degraded in the natural environment but can also be recycled like paper and cardboard.Inspired by the cross-linking structure of plant cell walls,a flame retardant and insulating pulp fiber foam with laminar structure and anisotropic mechanical properties was prepared,where the borate bonded covalently with oxygen-containing functional groups,and the CNF stabilized the foam.The results showed that the foam has low density（12.1mg/cm³）and high porosity（99.2%）.The CNF aggregated around the bubble and the boundary,which weakens the coarsening process of the bubble and improves the foam stability.A laminar structure of a three-dimensional network was formed by mechanical shear and gravity,and the CNF formed a complex network structure between the fiber layers.The foam exhibits anisotropic mechanical properties,with good resilience in the Z-direction（74.4%）and high strength in the X-direction（with modulus and specific modulus of 195.1 k Pa and 15.3 MPa·cm³/g）.The foam achieved excellent flame retardant properties at low boron content.The PHRR was decreased by 57.3%and the limiting oxygen index was up to 23.5%.The foam also exhibited good thermal insulation performance with a low thermal conductivity of 48.6 m W/m K and excellent thermal stability.