Because of the uneven colour of black locust wood, different technologies are used to change the colour, the bestknown being chemical and thermal treatments. Some of them affect the mechanical properties of wood, such as elasticity modulus, strength, durability. This study aims to compare the physical and mechanical properties of black locust wood control samples and treated wood samples with ammonia hydroxide, in terms of density profile, colour values (CIE L*, a*, b*), mechanical properties of samples subjected to static bending, viscous-elastic properties (storage modulus (E’), loss modulus (E”) and damping (tanδ)). Two types of ammonia-fuming treatment were applied on samples: first treatment T1-5% concentration of ammonia hydroxide for 30 days; second treatment T2-10% concentration for 60 days. The results highlighted the following aspects: the overall colour change in the case of the second treatment is 27% in comparison with 7% recorded for the control samples; the lightness and yellowness values are the most affected by the second ammonia treatment of black locust wood. The density increased with almost 20% due to ammonium fuming (10% concentration/60 days); in case of static bending, the elastic modulus (MOE) tends to decrease with increasing the exposure time to ammonium, but the modulus of rupture (MOR) increases with almost 17% and the breaking force increases too, with almost 41%. In the case of dynamic mechanical analysis, the temperature leads to different viscous-elastic behaviour of each type of samples.

Modeling dynamic heterogeneity in amorphous shape memory polymers (SMPs) is a huge challenge due to the complex statistics of strain energy distributions during their thermodynamic relaxations. In this study, based on the dynamic heterogeneity of strain energy distribution, we have considered, for the first time, the influences of different temperature rates and strain rates on strain energy evolution as a dynamic equilibria, rather than a quasi-static problem. We propose a phase transition model incorporated with Gaussian distribution statistics to investigate the dynamic equilibria with glass transition heterogeneity and tailorable mechanics for the amorphous SMPs. The Gaussian distribution statistics is firstly applied to characterize the heterogeneity of strain energy distributions in the amorphous polymers. Phase transition theory is then developed to describe working principles of strain energy evolution, glass transition heterogeneity, thermodynamic relaxation and tailorable mechanics. Finally, the dynamic equilibria of heterogeneity about the statistics of strain energy distribution are formulated based on the one dimensional Maxwell multi-branch model. The analytical results are compared with the experimental data of epoxy, polyamide and vinylester SMPs reported in literature, and good agreements between them are demonstrated. This study provides a new insight into the dynamic heterogeneity in the mechanics of amorphous SMPs.

Highly entangled gels have gained extensive attention due to their excitingly large deformation and high toughness. To understand the toughening mechanism of these highly entangled gels, an entanglement constraint model has been established, based on the spatially prismatic constraint and Gaussian distribution models. A free-energy function is formulated to study the conformational dynamics, rubbery elasticity and sliding effect of topological knots in the entangled chains. Monte Carlo, molecular dynamics and finite element analysis were conducted to verify the coupling effect of inter-chain entanglement and intra-chain knot topology on the toughness behavior of highly entangled gels. Finally, experimental data available in the literature were used to verify the proposed models, providing a physical insight into the toughening mechanism of inter-chain entanglement constraint and intra-chain knot topology in the highly entangled gel.

Coexistence of multiple and discrete segments as well as their distinctive hysteresis relaxations enables amorphous shape memory polymers (SMPs) exhibiting complex disordered dynamics, which is critical for the glass transition behavior to determine the shape memory effect (SME), but remained largely unexplored. In this study, a dynamic hysteresis model is proposed to explore the working principle and collective dynamics in discrete segments of amorphous SMPs, towards a dynamic connection between complex relaxation hysteresis and glass transition behavior, which can be applied for design and realization of multiple SMEs in the amorphous SMPs. In combination of free volume theory and Adam-Gibbs domain size model, a phase transition model is formulated to identify the working principle of dynamic relaxation hysteresis in the glass transition of amorphous SMP. Furthermore, constitutive relationships among relaxation time, strain, storage modulus, loss angle and temperature have been established to describe the dynamic connection between complex relaxation hysteresis and customized glass transition, which is then utilized to achieve multiple SMEs based on the extended Maxwell model. Finally, effectiveness of the proposed models is verified using experimental results of SMPs with multiple SMEs reported in literature.

The problem of industrial use of tree bark is relevant and has practical importance for complex processing of wood raw material. Barks are available in Hungary and Russia in large quantities, but they are not widely used for different purposes than producing energy. One of the perspective areas of utilization of tree bark is its use as raw material for the production of thermal insulation panels. The present study focuses on the thermal insulation capacity of tree bark. Thermal conductivity properties of two broadleaved (black locust (Robinia pseudoacacia), pannónia poplar (Populus euramericana cv. Pannónia)) and three coniferous (larch (Larix decidua), spruce (Picea abies) and scots pine (Pinus silvestris)) tree species were examined. Based on these results, the scopes of the tested species were further narrowed, while the best results showing black locust was used for pressed insulation panel. Three different fractions were produced made of grained black locust bark. Furthermore, the heat insulation capacities of bark were investigated by compressing the chipped bark particles until the lowest heat conductivity was reached. Results show a competitive thermal insulation property to the traditionally used insulation materials, the value was 0.0613 W/mK reached by black locust bark chips. The broadleaved tree bark chips have a lower thermal conductivity than coniferous species. By using fine, mid, and coarse fraction of black locust bark were produced and the difference of thermal conductivity between them was negligible. Although the fine fractionated black locust bark chip thermal conductivity was 0.042 W/mK.