Influence of temperature and pressure during thermoforming of softwood pulp

In this study,the influence of thermoforming conditions on the resulting material properties was investigated,which aimed at developing advanced wood-fiber-based materials for the replacement of fossil plastics.Two bleached softwood pulps were studied,i.e.,northern bleached softwood Kraft pulp(NBSK)and chemi-thermomechanical softwood pulp(CTMP).The thermoforming conditions were varied between 2–100 MPa and 150–200℃,while pressing sheets of 500 g/m^(2)for 10 min to represent thin-walled packaging more closely.As our results showed,the temperature had a more pronounced effect on the CTMP substrates than on the Kraft pulp.This was explained by the greater abundance of lignin and hemicelluloses,while fibrillar dimensions and the fines content may play a role in addition.Moreover,the CTMP exhibited an optimum in terms of tensile strength at intermediate thermoforming pressure.This effect was attributed to two counteracting effects:1)Improved fiber adhesion due to enhanced densification,and 2)embrittlement caused by the loss of extensibility.High temperatures likely softened the lignin,enabling fiber collapse and a tighter packing.For the Kraft substrates,the tensile strength increased linearly with density.Both pulps showed reduced wetting at elevated thermoforming temperature and pressure,which was attributed to hornification and densification effects.Here,the effect of temperature was again more pronounced for CTMP than for the Kraft fibers.It was concluded that the thermoforming temperature and pressure strongly affected the properties of the final material.The chemical composition of the pulps will distinctly affect their response to thermoforming,which could be useful for tailoring cellulose-based replacements for packaging products.

Alternative wood treatment with blends of linseed oil,alcohols and pyrolysis oil

Linseed oil is a common wood treatment agent,which is often blended with naphthenic oil during its application.In this study,we developed new types of linseed oil blends,where the naphthenic oil was substituted with alcohols and pyrolysis oil.As miscibility tests revealed,linseed oil can be blended indefinitely with primary alcohols containing three carbon atoms or more.In addition,kinetic stability of three-component-mixtures was found,which comprised linseed oil,alcohol and pyrolysis oil.The developed blends were further tested for their viscosity and rate of solvent evaporation.At last,trial impregnations of wood were done to test this new treatment agent.The uptake of treatment oil and the effect on water repellency varied,and substituting white spirit with propanol and pyrolysis oil showed potential.The latter were miscible with 50%(wt)linseed oil at concentrations of 37.5%1-or 2-propanol and 12.5%pyrolysis oil.Compared with the reference case,treatment with this agent markedly decreased the water-uptake of the wood.Our study hence attributes great potential to the newly developed linseed oil blends,which may introduce additional product characteristics and generate value to byproducts via pyrolysis.