Bamboo Bundle Laminated Veneer Lumber Research Articles

Effects of bamboo nodes on mechanical properties of thin-type bamboo bundle laminated veneer lumber (BLVL): From anatomical structure to penetration mechanism

As a lightweight and high-strength green structural material, thin-type bamboo bundle laminated veneer lumber (BLVL) has been widely used in construction and transportation. However, bamboo nodes are often discarded as mechanical weak links during production and preparation. For the dredged bamboo bundle fiber, a large number of discontinuous fibers are found at the node, which are not conducive to the mechanical strength of BLVL. But on the other hand, the loose structure of the bamboo node facilitates the penetration and curing of the phenolic resin, which improves the bonding and mechanical strength of BLVL. Therefore, the influence rule by what bamboo nodes affect the mechanical properties of thin-type BLVL remains unclear. In this study, the effects of bamboo nodes and their distribution positions on the mechanical properties of thin-type BLVL were studied, and the underlying mechanism was identified from the perspective of assembly and bond penetration theory. Our findings indicate that the existence of bamboo node improves the bending strength (150.78 ± 29.24 MPa) and fracture toughness (2.58 J/cm2) of thin-type BLVL, but it’s still a potential weak link during stretching because of the influence of broken fibers. Considering that the tensile strength of thin-type BLVL exceeds practical standards, we suggest retaining bamboo nodes during production and processing, and the bamboo nodes should also be evenly distributed as far as possible during billet formation to maximize the use of bamboo without compromising its efficiency.

Bamboo-inspired strong, tough and stable composites derived from renewable bamboo

Bamboo engineering materials are made from abundant raw material sources and can be easily prepared with minimal processing and low pollution. However, when used as structural materials, they are limited by their weight, strength, and lack of stable designability. The use of laminated structure and a gluing interface are key factors affecting the performance of bamboo engineering materials. Bamboo exhibits excellent toughness and strength when resisting external forces, with a multi-level interlocking reinforced interface with bamboo’s intercellular layer that induces an increase in crack deflection paths (internal toughening) and cell wall energy consumption (external toughening) coupled to microfibril pulling out. Inspired by the functionally graded structure of the lightweight and high-strength bamboo wall layer and the interlocking reinforced interface between vascular bundles and parenchyma cells, we designed a high-performance bamboo engineering material designed to imitate bamboo, Imitation Bamboo Bundle Laminated Veneer Lumber (IBLVL), prepared by uniform lamination and gradient molding. The designed IBLVL is light in weight, with high strength and uniform density. This work demonstrates the feasibility of using resource-rich and sustainable bamboo to manufacture light-weight bamboo engineering materials with high strength and high toughness that can be substituted for non-renewable resources in the fields of construction and transportation.

Fiber bundle recombination and gradient uniform lamination to process high-strength and tough bamboo engineering materials

In addition to high strength and stiffness, advanced structural engineering materials and components should also have designability and structural stability. Green building structural materials developed using bamboo face challenges in terms of durability and stability. In this work, we utilize fiber reorganization and gradient uniform lamination a high-strength, high-toughness, uniform and durable outdoor bamboo engineering material- Bamboo Bundle Laminated Veneer Lumber（BLVL) was prepared by the method of. The unique interlayer tight laminated interlocking occlusal structure and the glue nails enhance the interface bonding performance enhanced BLVL performance. The BLVL specific strength, specific modulus, and impact toughness were 267.70 MPa cm3 g−1, 20.73 GPa cm3 g−1, and 13.8 J/cm2, respectively. The density uniformity and dimensional stability were 2.47 and 2.24 times higher than those of the bamboo scrimber (BS), respectively. This work demonstrates the potential to produce lightweight durable structural engineering materials with controllable properties and designable structures from abundant sustainable fast-growing bamboos.

Evaluation of Uniformity of Bamboo Bundle Veneer and Bamboo Bundle Laminated Veneer Lumber (BLVL)

The lack of an effective and practical quality control method for industrialized bamboo bundle veneers is the key restriction in the application of bamboo bundle composite materials in the field of construction. In this work, the density uniformity and mechanical properties of bamboo bundle veneers were systematically evaluated by the combination of light transmittance and mechanical stiffness. It was found that the number of broomings, dippings, and high-temperature heat treatments had different effects on the bamboo bundle veneers. On this basis, the uniformity of the density and mechanical properties of the bamboo scrimber (BS) that underwent hybrid paving, and the bamboo bundle laminated veneer lumber (BLVL), were analyzed. The results showed that the performance stability of bamboo bundle composites could be greatly improved by bamboo bundle veneer laminated paving. A large-scale quality evaluation system for bamboo bundle veneers was established in this work, and it provides conditions for the manufacture of bamboo bundle composites with stable and controllable performance.

Process Optimization of Large-Size Bamboo Bundle Laminated Veneer Lumber (BLVL) by Box-Behnken Design

This work focuses on optimization of the laminated lap-joint lengthening technology that is used to produce large-size bamboo bundle laminated veneer lumber (BLVL). A three-factor Box-Behnken design was developed in which lap-joint length (x1), board density (x2), and thickness of lap veneer (x3) were the three factors. Multi-objective optimization of response surface model was used to obtain 17 optimum Pareto solutions by a genetic algorithms method. The mechanical properties of BLVL predicted using the model had a strong correlation with the experimental values (R2 = 0.925 for the elastic modulus (MOE), R2 = 0.972 for the modulus of rupture (MOR), R2 = 0.973 for the shearing strength (SS)). The interaction of the x1 and x3 factors had a significant effect on MOE. The MOR and shearing SS were significantly influenced by the interaction of x2 and x3 factors. The optimum conditions for maximizing the mechanical properties of BLVL lap-joint lengthening process were established at x1 = 16.10 mm, x2 = 1.01 g/cm3, and x3 = 7.00 mm. A large-size of BLVL with a length of 14.1 m was produced with the above conditions. Strong mechanical properties and dimensional stability were observed.

Effects of Aging Temperature on Mechanical Performance of Bamboo Bundle Laminated Veneer Lumber Joints Prepared by Intermittent Hot Press Process

Recently, an intermittent hot-pressing process had been developed and applied to produce bamboo bundle laminated veneer lumber (BLVL) joints with lengths of more than 6 m. According to our previous studies, there was a major difference in the physical and mechanical performance of hot-pressing joints and at adjacent positions on the lumber. In this paper, heat transfer and the effects of various aging temperatures on the mechanical performance of the joints of intermittent hot-pressed BLVLs were studied. During the hot-pressing process, there were noticeable different temperature changes on the board. In addition, degradation of the modulus of elasticity (MOE) and modulus of rupture (MOR) values on the joints was greater than that on the adjacent positions of the BLVLs, and the degradation increased with increasing aging temperature. Because of the low interfacial bonding strength of the joints caused by the pre-curing effect during the hot-pressing process, the MOR was more sensitive to hydrothermal conditions. Therefore, when BLVLs produced by intermittent hot-pressing are used as engineering components, the joints should be well-designed and arranged to avoid being used in the same cross-section.

An empirical model for predicting the mechanical properties degradation of bamboo bundle laminated veneer lumber (BLVL) by hygrothermal aging treatment

An empirical 3-D model was developed to evaluate the effect of ambient environment on the mechanical properties and degradation behavior of bamboo-bundle laminated veneer lumber (BLVL) fabricated with different levels of PF/PVAc resin. This model can describe the relationship between the modulus of elasticity (MOE), water absorption ratio, and aging temperature. Five levels of PF/PVAc weight ratio (2:1, 4:1, 6:1, 8:1 and 10:1) and three treatment conditions (18, 63, and 100 °C) were examined in this experiment. Computed tomography (CT) scanning technology was employed to observe the morphology of damage degree as well as explore the mechanism of degradation behavior of BLVL. The results indicated that the 3-D model used for tracking and monitoring the variance of MOE provided good predictors. The higher the water impregnation temperature the larger the water absorption ratio and the higher the MOE degradation were. The aging temperature had a significant effect on the mechanical properties and degradation behavior of BLVL. A linear relationship between modulus of rupture (MOR) degradation and aging temperature was observed. The degradation rate of MOE and MOR increased as the temperature increased. The aging degree tested by CT along with damage of inner board showed the PF/PVAc ratio had a significant influence on the mechanical degradation of treated BLVL when the PF/PVAc ratio was below 6:1. Localized yielding, micro-cracks developing between interfaces, PVAc resin softening along with delamination, and debonding were the main failure models for the BLVL by hygrothermal aging treatment.

The bending properties of bamboo bundle laminated veneer lumber (BLVL) double beams

Large span bamboo bundle laminated veneer lumbers (BLVLs) were prepared by combining the prepress densification process and the intermittent hot press process. Their mechanical performances of the intermittent hot joints and adjacent positions were also investigated. Based on this, a new type of BLVL double-beam members was developed and their bending properties including ultimate load, static bending strength and strain distribution were systematically analyzed by comparing with other double beams with different members. The results showed that large span BLVLs could be well prepared by intermittent hot press process and its mechanical properties could meet the requirements of 160-E superior products according to Chinese national standard GB/T 17657-2013. Besides, the values for the cross-section flexural rigidity and bending modulus of BLVL double beams were extremely high. Bamboo-wood composites (BWC) double beams with more ductility coefficient had a great ability of plastic deformation. For these double beams, the cross-section stiffness was the first factor which to be considered and optimized and the change of the strain along thickness direction was linear, which was in line with the hypothesis theory of bending plane of materials. This study was finally beneficial to design, manufacture, and application of bamboo-based structural engineering materials with lightweight, low cost, and excellent mechanical performances by supplying financial data support.

Evaluation of Water Absorption and its Influence on the Physical-Mechanical Properties of Bamboo-Bundle Laminated Veneer Lumber

To investigate the possibility of using bamboo-bundle laminated veneer lumber (BLVL) as a cooling tower packing material, the water absorption rates, thickness swelling rates, and flexural properties of three different composite materials were studied. The BLVL was combined with either 12% or 24% phenol formaldehyde resin (PF), and the moso bamboo strips were exposed to water baths at three different temperatures (45, 65, and 85 °C) for 30 d. After the aging treatments, the 24%-BLVL samples showed lower water absorption rates and better bending properties than the other two composites. The temperature was found to have a significant effect on the modulus of rupture (MOR), modulus of elasticity (MOE), and the thickness swelling rate. As the temperature increased, the swelling rate and the rate of weight gain increased and the MOE and MOR decreased. According to the activation energies for swelling calculated from the Arrhenius-type plots, compared with the 24%-BLVL (22.95 kJ·mol-1) and the moso bamboo strips (12.69 kJ·mol-1), the effect of temperature on the swelling rate was greatest for the 12%-BLVL (24.15 kJ·mol-1). Results showed that the BLVL material is a promising candidate for a novel cooling tower packing material.

The effect of PF/PVAC weight ratio and ambient temperature on moisture absorption performance of bamboo‐bundle laminated veneer lumber

The veneer preprocessing densification is a vital procedure in the manufacturing process of long‐span bamboo‐based engineering material, bamboo‐bundle laminated veneer lumber (BLVL). The adhesive used in the preprocessing densification process was the mixture of phenol formaldehyde (PF) resin and polyvinyl acetate (PVAC) resin. The objective of this study was to investigate the effect of PF/PVAC weight ratio on the moisture absorption performance of BLVL, as well as the effect of ambient temperature on the hygroscopic swelling performance for BLVLs with a PF/PVAC ratio of 6:1. The results indicated that the water absorption swelling rate and weight gain rate of the BLVLs decreased as PF/PVAC ratio increased at 63°C. The absorption behavior of BLVL was found to obey Fick's law at 63°C approximately. The higher the PF/PVAC ratio, the lower swelling parameter KSR and D values were obtained. However, PF/PVAC ratio exerted little effect upon the bending properties(modulus of rupture and elasticity) of BLVL. Temperature has a significant effect on the moisture absorption performance of BLVL (6:1 PF/PVAC ratio). The higher the temperature, the greater swelling and weight gain rate was obtained, as well as KSR and D values. The calculated swelling activation energies (ES) were 25.79 and 22.45 KJ mol−1 for BLVLs with 6:1 PF/PVAC ratio and the ones with neat PF resin, respectively, while the diffusion activation energies (ED) were 10.62 and 8.47 KJ mol−1. POLYM. COMPOS., 37:955–962, 2016. © 2014 Society of Plastics Engineers

The Effect of Joint Form and Parameter Values on Mechanical Properties of Bamboo-Bundle Laminated Veneer Lumber (BLVL)

Bamboo-bundle laminated veneer lumber (BLVL) was produced by joint lengthening technology. The objective of this study was to evaluate the effect of joint form and the values of key parameters on mechanical properties of BLVL. Two joint forms, i.e., finger joint and scarf joint, and two corresponding joint parameters, i.e., finger length and scarf angle, were investigated in laminates. The results indicated that the mechanical properties of jointed BLVL were reduced in comparison to those of BLVL without joints. For finger-joint form, the BLVL member with 14 mm fingers achieved better compressive strength, bending modulus of rupture (MOR), and tensile strength than 19 and 25 mm ones. For scarf-joint form, the 30° scarf-jointed member exhibited the highest bending modulus and tensile modulus of rupture (MOR) in this study, then followed the 45° and 60° ones. The 60° scarf-jointed BLVLs were better than 30° and 45° groups in compression strength. Synthesis of the testing results revealed that finger-jointed BLVLs achieved better bending modulus of rupture than scarf-jointed ones.

Impact properties of bamboo bundle laminated veneer lumber by preprocessing densification technology

The objective of this study was to investigate the deformation behavior of bamboo bundle laminated veneer lumber (BLVL) manufactured with veneer preprocessing densification technology under low velocity impact loading. The influence of different preprocessing temperatures, times, and stacking sequences was studied with respect to impact loading. Laminates with bamboo bundles parallel to the length direction were labeled as type I, and cross-ply was labeled as type II. The results indicated that delamination and fiber breakage were the main damage models for BLVL made with veneer preprocessing densification technology, and its impact performance under a veneer prepressing temperature of 90 °C and a time of 10 min was fairly comparable to that of BLVL without preprocessing densification. The impact index decreased as the densification temperature increased. The impact properties for type II were better than that of type I. The curve characteristic of impact deflection vs. time presented a linear trend, while the curve of impact velocity first decreased and then tended to level off as time elapsed.

Effect of Different Veneer-joint Forms and Allocations on Mechanical Properties of Bamboo-bundle Laminated Veneer Lumber

Bamboo-bundle laminated veneer lumber (BLVL) was produced by veneer lengthening technology. The objective of this study was to evaluate the effect of different veneer-joint forms and allocations on the mechanical properties of BLVL. Four veneer-joint forms, i.e., butt joint, lap joint, toe joint, and tape joint, and three lap-joint allocations, i.e., invariable allocation (Type I), staggered allocation (Type II), and uniform allocation (Type III), were investigated in laminates. The results revealed that the mechanical properties of veneer-joint BLVL were reduced in comparison with that of un-jointed BLVL. It was found that the best veneer-joint form was the lap joint laminate, of which the tensile strength, modulus of elasticity, and modulus of rupture values were reduced by 38.41%, 0.66%, and 10.92%, respectively, when compared to the un-jointed control samples. Type III showed the lowest influence on bending and tensile properties, followed by Type II.

Evaluation of the Uniformity of Density and Mechanical Properties of Bamboo-Bundle Laminated Veneer Lumber (BLVL)

The objective of this study was to evaluate the uniformity of density distribution for Bamboo-bundle Laminated Veneer Lumber (BLVL) and its relationship to the stability of mechanical performance. A novel assembly style called one-piece veneer formation technology was developed to enhance the density uniformity, and four different density levels for BLVL were examined by X-ray scanning. The results indicated that the homogeneity of density, the stability of mechanical performance, and the mechanical properties for BLVL could be effectively improved by assembling the bamboo bundles into layers and then combining the layers to make the lumber. The density uniformity in width and thickness directions increased with increasing target density. A negatively linear correlation between density and Coefficient of Variation (COV) of MOR and shearing strength was observed. Partial correlation analysis revealed that when controlling for the variability of density, the linear relationship between density and the COV of MOR became insignificant, and the degree of linear correlation between density and the COV of shearing strength decreased.