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Inspiration from Table Tennis Racket: Preparation of Rubber-Wood-Bamboo
Laminated Composite (RWBLC) and its Response Characteristics to Cyclic
Perpendicular Compressive Load
Jianchao Deng, Xin Wei, Haiying Zhou, Ge Wang, Shuangbao Zhang
PII: S0263-8223(19)34824-X
DOI: https://doi.org/10.1016/j.compstruct.2020.112135
Reference: COST 112135
To appear in: Composite Structures
Received Date: 23 December 2019
Revised Date: 1 February 2020
Accepted Date: 25 February 2020
Please cite this article as: Deng, J., Wei, X., Zhou, H., Wang, G., Zhang, S., Inspiration from Table Tennis Racket:
Preparation of Rubber-Wood-Bamboo Laminated Composite (RWBLC) and its Response Characteristics to Cyclic
Perpendicular Compressive Load, Composite Structures (2020), doi: https://doi.org/10.1016/j.compstruct.
2020.112135
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Inspiration from Table Tennis Racket: Preparation of Rubber-Wood-Bamboo
Laminated Composite (RWBLC) and its Response Characteristics to Cyclic
Perpendicular Compressive Load
Jianchao Deng a, b, Xin Wei b*, Haiying Zhou b, Ge Wang b*, Shuangbao Zhang a
aBeijing Key Laboratory of Wood Science & Engineering, College of Material Science & Technology, Beijing
Forestry University, No. 35 Tsinghua East Road, Haidian District, Beijing, P.R. China, 100083
bInternational Center for Bamboo and Rattan, No. 8 FuTong Eastern Avenue, Wangjing Area, Chaoyang District,
Beijing, P.R. China, 100102
*Corresponding author: Xin Wei; Ge Wang *Tel: +86 10-84789751
*E-mail: sunic_bamboo@126.com
Abstract
Inspired by table tennis racket, ten assembly patterns of 7-ply rubber-wood-bamboo laminated
composites (RWBLCs) were prepared, and physical, static destructive mechanics and pendulum impact
tests were conducted, seeking for the possibility of rubber protecting natural biomass material, for
better performance in the area of construction and transportation. The response of RWBLCs to cyclic
perpendicular compressive load and its sensitivity to temperature (140, 170, 200, 230, 260°C) were
analyzed. Results indicated that RWBLCs’ density raised as the proportion of rubber increased,
however hardly affect the lightweight design of laminated biomass composites. The structure PPPPPPP
performed the poorest underwater dimensional stability, while the opposite for RPPRPPR and
PRPRPRP. The RWBLCs RPPPPPR, RPPBPPR and RPBBBPR, had superior bending, shearing, and
pendulum impact capacity. Synthesis analysis of load-displacement curves, thickness decrement and
energy change implied that “table tennis racket” structures (RPPPPPR, RPPRPPR, RPPBPPR,
RPBBBPR, RPBB'BPR) achieved great damping aseismic performance and above-average
deformation resistance. As temperature increased, the degree of crystallinity of wood and bamboo
experienced a slight rise and distinct fall within 140~200°C and 230~260°C, respectively. Besides,
biomass material suffered evident pyrogenic decomposition of cellulose and lignin at 260°C that
RWBLCs could not withstand whole ten cycles of perpendicular compression, except RPPBPPR.
Keywords: Biomass material; rubber sheet; cyclic perpendicular compression; energy absorption;
degree of crystallinity
1 Introduction
Bamboo has received increasing attention as an alternative raw material to wood due to its rapid
growth rate (just 2~5 years per cycle), sustainable utilization (bamboo culm can be harvested multiple
times from a single planting), high specific strength and stiffness (2~3 times when compared to
fast-growing wood), superior toughness and surface hardness[1-3]. Bamboo processing is relatively
convenient, due to its orientation consistency of the vascular tissues (VTs) and parenchyma tissues
(PTs), as well as the absence of piths and transverse rays[4-5]. It can be cut into different kinds of
elementary manufacturing unit, and corresponding bamboo-based composites have been applied in a
variety of fields for decades, among which green construction and building is a sustainable and
promising area, while natural fiber reinforced laminated composites should be considered as one of the
most prevalent composite forms[6-11].
However, as natural biomass material, wood and bamboo are facing the challenge, including poor
dimensional stability due to the sensitivity to moisture and temperature, and weak biological durability
caused by vulnerability to fungi and insects, which limits their application[8,12-14]. Therefore,
protection and reinforcement should not be ignored upon such biomass material, for taking full
advantage of their characteristics and function as structural material (damping capacity or energy
absorption, lightweight and high strength, resistance to moisture/water swelling, etc)[15-16].
Table tennis racket is one kind of wood-based sandwich panel covered by rubber and sponge,
which has been proves to be an ingenious structure for this sport. The wooden plate offers elastic force
for rapid offense, while the rubber and sponge act as damping part and provide athletes with easy
defense. Inspired by the structure design of table tennis racket, rubber can be considered playing the
role of “bodyguard” for wood and bamboo, due to its unique advantages of high compressive
performance, low moisture absorption, good damping vibration attenuation, excellent energy
absorption, characteristically large elastic deformation, better sound insulation, good durability,
abrasion resistance, anti-caustic and anti-rot properties[17-20]. Thus, the rubber-wood-bamboo hybrid
composite laminates would have multi-functional properties and excellent potential for extended
applications (container soleplate, flooring of train carriage & fabricated building, etc).
In recent years, many studied have been done about the utilization of rubber particles in hybrid
wood or bamboo composite panel, where the size of natural fibers ranged from micrometer to
millimeter-level, i.e. wood fibers (with a length-width ratio of 5:45)[21], wood particles (3~25 mm in
length, 1.0~2.5 mm in width, and 0.2~0.8 mm in thickness)[22-23], wood flour (400 μm)[24], bamboo
powder (180~270 μm)[25], etc. These research articles paid much attention to the effect of functional
unit content, adhesive type, and processing parameter on physical (micro-structure of wood-rubber
interface, water resistance and sound insulation) and mechanical properties (bending toughness,
internal bond strength). However, compressive performance, damping capacity or energy absorption of
wood/bamboo-rubber hybrid composite, has not been studied specifically, which should not be ignored
for application likewise.
The utilization of rubber in plywood was also reported that rubber powder was firstly hot pressed
into panel as core or middle layer, and then wooden veneers and rubber layer were pressed into hybrid
plywood panel[26]. Results indicated that the physical properties (water absorption and thickness
swelling) of the manufactured panels were improved, while the opposite for the mechanical properties
(modulus of rapture, elasticity (MOR, MOE) and impact strength), as rubber content increased.
Nevertheless, the effect of the amount and location of rubber layer (not only middle layer) upon the
performance of composites laminates was not investigated. In addition, few literatures described
rubber-wood-bamboo hybrid composites, rather than wood-bamboo, wood-rubber, or bamboo-rubber
ones.
In this paper, ten different patterns of assembly for 7-ply rubber-wood-bamboo laminated
composites (RWBLC) were designed and prepared, and corresponding physical (density, thickness
swelling rate of water absorption), static destructive mechanics (bending, vertical shear,
parallel-to-grain tensile) and pendulum impact tests were conducted, to analyze the apparent
performance among different assembly patterns. Besides, perpendicular compressive load was applied
cyclically upon RWBLCs within certain limits, aiming at investigating the laminated composites’
compressive performance or energy absorption behavior. Herein, five temperature gradients were
adopted as different treatment conditions, in consideration of temperature sensitivity of natural biomass
material (wood and bamboo).
2 Material and Methods
2.1 Preparation of RWBLCs
2.1.1 Preparation of wood veneer
The poplar (Populus ussuriensis Kom.) of more than ten years old was obtained from Cangzhou,
Hebei Province, China. The average diameter at breast height for poplar was 50 cm and the overall
height of the tree was over 20 m. Non-deficient, knotless and normally grown wood materials were
selected to make 1.2 mm-thick veneer using rotary cutting machine, with a moisture content (MC) of
8%~12%.
2.1.2 Preparation of bamboo bundle veneer
Four-year-old moso bamboo (Phyllostachys pubescens) was grown in Nanchang, Jiangxi
Province. Bamboo tubes with a diameter at breast height of no less than 100 mm were first split into
several pieces of approximately the same size, with bamboo yellow, green and nodes being removed.
Bamboo strips were then rolled and broomed into loosely reticulate sheets with certain uniformity of
thickness (1.7 mm). Such sheets were cross-linked in the width direction with no fracture along the
length direction, maintaining the original bamboo fiber arrangement (Fig. 1). The bamboo bundle
veneers were finally cut into pieces of 300 mm in length and air-dried to a MC between 8% and 12%.
Fig. 1. Preparation of bamboo bundle veneer
2.1.3 Preparation of rubber sheet
Synthetic rubber sheet bought from Shanghai Laike rubber products & engineering plastics Co.
Ltd (Shanghai, China) was made by Ethylene-Propylene-Diene Monomer (EPDM) and Styrene
Butadiene Rubber (SBR), with a thickness of 1 mm, hardness of 70° and vulcanizing temperature of
140°C.
2.1.4 Preparation of resin
Phenol formaldehyde (PF) resin used in the experiment was obtained from Beijing Dynea
Chemical Industry Co. Ltd (Beijing, China). The PF resin (with an initial solid content of 47% and pH
of 11~12) was diluted with water to a solid content of 30% as the adhesive, in which the bamboo
bundle veneers were immersed for 10 min and then dried to a MC of 8%~12%. For wood-wood and
wood-bamboo interface, one-faced brush coating of PF resin (150g/m2, solid content of 23.5%) was
applied to wood veneer.
Triphenylmethane triisocyanate (TTI), with the molecular formula (C6H4NCO)3CH, was obtained
from Liaoning Hongshan Chemical Industry Co. Ltd (Kazuo, China) and used as wood-rubber bonding
adhesive, due to the possession of highly reactive and unsaturated-NCO groups (Zhao et al. 2008). The
performance parameters of the resin were shown herein (substantial content of 20%±1%, one-faced
brush coating of 80 g/m2 onto rubber sheet, bonding strength≥4.0 MPa).
2.1.5 Design and preparation of RWBLCs
To prevent board sticking to hot platens, waxed papers were placed at the bottom and on the top of
the mat. Seven layers of wood veneers (WVs), bamboo bundle veneers (BVs) and rubber sheets (RS)
were assembled one by one, and the RWBLC was shaped at a platen temperature of 140 °C (15 min
pressing time, 4 MPa pressing pressure). Ten different patterns of assembly for the 7-ply RWBLC were
designed and prepared in this paper, including PPPRPPP, PPRPRPP, PRPPPRP, RPPPPPR,
RPPRPPR, PRPRPRP, RPPBPPR, RPBBBPR, RPBB'BPR, and PPPPPPP, as Fig. 2 shows. These
boards were stored in a normal room environment, where they were air-dried to a MC of 9.5%~10.5%.
Fig. 2. Preparation of RWBLCs
Note: P, B, R mean one layer of poplar veneer, bamboo bundle veneer, and rubber sheet respectively.
B’ means the one vertical to B. The value in parenthesis represents serial number of different laminated
design in sequence.
2.2 Tests and Measurement
2.2.1 Physical properties tests
Thickness swelling rate after 2, 4, 8, 12, 24, and 72 h of underwater immersion, as well as the
boards’ density, were obtained, referring to Chinese national standard GB/T 17657-2013[27].
2.2.2 Static destructive mechanics and pendulum impact tests
Three-point bending, shearing, and parallel-to-grain tensile tests were conducted in accordance
with the Chinese national standard GB/T 17657-2013[27], using a universal testing machine (Instron
5582, Norwood, MA USA). Different assembly patterns of RWBLCs, with a size of 100 mm * 10 mm
* t (thickness), were subjected to impact test by a pendulum impact tester (ZBC 1151-1, Shenzhen
Sansi Material Testing Co. LTD, Shenzhen, China), referring to ASTM D6110-2018[28]. Eight
duplicates had been prepared for each tests, and bending MOE, MOR, vertical shearing,
parallel-to-grain tension, and impact strength were obtained, respectively.
2.2.3 Cyclic perpendicular compressive behavior evaluation
The perpendicular compression mode of ten cycles of “slow loading-fast unloading” was designed
that the unloading began immediately the loading (2.5 mm/min) value reached a customized maximum
load (3 kN), and then the following cycle started towards the 20 mm * 20 mm * t (thickness) specimens
for different types of RWBLCs.
Load-displacement curves were obtained for every cycle, and the change of energy value
(absorption or dissipation) was discussed using graphical integration. The cross sections of RWBLCs
were observed using a stereo light microscope (INFINITY3-6URC) combined with the software
Image-Pro Plus (Media Cybernetics, USA), and the thickness of each layer (wood, bamboo, or rubber)
before and after perpendicular compression was calculated.
In consideration of temperature sensitivity of natural biomass material (wood and bamboo), five
temperature gradients were determined as different conditions. Before cyclic compression, specimens
were stored in drying oven (FD 115, Binder Co., Germany) at 140, 170, 200, 230, or 260°C for an
hour, respectively. To study the effect of condition temperature on RWBLCs’ cyclic perpendicular
compressive behavior, load-displacement curves were compared, and the analysis was done on
chemical component and crystallinity change.
2.2.4 Chemical component, crystallinity and micro-deformation analysis
Wood and bamboo powders were smashed and sieved, and the fraction of 60 mesh experienced
firstly 140, 170, 200, 230, or 260°C drying treatment in an oven (an hour), respectively. Dry sample
powders (Fig. 3) and potassium bromide (KBr) were mixed at a mass ratio of 1~1.5 % in an agate
mortar, and milled repeatedly under infrared irradiation until a uniform mixture was achieved. The
powder mixture was then pressed into a transparent pellet for the scan in the wave number of 4000~400
cm-1 with a resolution of 4 cm-1, using a Spectrum One FTIR spectrometer (Nexus670, Nicolet, USA).
And further the analysis of chemical functional group variation of wood or bamboo powders from
different temperature was done.
The degree of crystallinity of wood and bamboo powders was obtained by means of X-ray
diffraction spectrometer (XRD) using a Bruker D8 Advance instrument from USA (Cu-K,
Bragg-Brentano Geometry). The 2θ value for all powder samples was recorded from 10° to 90° with a
step size of 0.05°/s using Cu Kα radiation (40 kV, 40 mA).
Besides, the microstructure-scale compressive deformation was illustrated by scanning electron
microscope (SEM; Quanta 2000, FEI Company, Hillsboro, OR, USA) at an accelerating voltage of 20
kV.
Fig. 3. Preparation of wood and bamboo powders treated on different temperature conditions
2.2.5 Statistic analysis
Data were analyzed using a one-way analysis of variance (ANOVA) with the Duncan test using
SPSS 18 software (SPSS, Inc., Chicago, IL, USA). Probability values of less than 5% were considered
to be significant (p ＜0.05). Graphs were drawn using Origin 8.0 software (OriginLab Corp.;
Northampton, MA, USA).
3 Results and Discussion
3.1 Physical properties
Thickness swelling rate after 2, 4, 8, 12, 24, and 72 h of underwater immersion, as well as the
boards’ density, are presented in Fig. 4.
The composites made of pure poplar veneers (pattern 10) possessed the lowest density, while the
opposite for those manufactured with the largest amount of rubber sheets (pattern 5 and 6), due to
rubber’s higher density than the porous natural biomass material wood/bamboo. Correspondingly,
pattern 10 achieved the highest thickness swelling rate (72h), while pattern 5 and 6 had the lowest,
which was attributed to the quantity of hydrophilic material wood (many adsorption sites) and
nonabsorbent material rubber. In comparison to pure wooden laminated composites (0.60 g·cm-3), the
addition of rubber did increase boards density, however the RWBLCs’ density in this paper (0.67~0.92
g·cm-3) remained lower than that of other laminated composites used as engineering material likewise
in some literature[9,29-30], which indicated that the presence of rubber exerted little influence on the
lightweight design of biomass based composites in construction and transportation area.
Fig. 4. Density and water absorption
Note: Different capital letters indicate a significant difference (p < 0.05) in density and thickness
swelling rate for different patterns of assembly for RWBLCs.
It can also be noticed in Fig. 4 that board thickness swelling rate increased relatively rapidly
during the initial stage (0~10 h), as the water entered into wood and bamboo, and occupied the pore
and void spaces gradually. Additionally, part of the swelling was a result of springback when the
internal stress induced during hot pressing was released as moisture diffused and penetrated into the
board[31]. As time elapsed, the swelling would continue at a progressively slowing rate before it
tended to level off because the swelling of a majority of the wood and bamboo elements were
completed[8]. Similar parabola trend was also observed elsewhere[8,31].
Fitted curves of absorption thickness swelling rate (%) and underwater immersion time (h) of
different patterns of assembly for RWBLCs are presented in Fig. 4, and can be expressed as the
following equation,
y = A * exp (-x/a) + b(1)
where y is thickness swelling rate (%), a and b are two constant values, and x is immersion time (h). In
Eq. 1, x and a are positive numbers that f(x)=-x/a and f(x)=exp (-x/a) are decreasing functions.
Meanwhile, -A is a positive number, so y=(-A)·[-exp (-x/a)]+b is an increasing function (in accordance
with the trends of fitting curves), which indicates that the value of A reflects how fast the RWBLCs’
water absorption and thickness swelling acted in some degree.
As presented in Fig. 4, the highest -A value (7.150) tells that pattern 10 performed the fastest
water absorption and thickness swelling, i.e. the poorest underwater dimensional stability, due to the
presence of more adsorption sites inside than others, while the opposite for pattern 5 and 6.
3.2 Static destructive mechanics and pendulum impact performance
Three-point bending MOE, MOR, vertical shearing strength(VSS), parallel-to-grain tensile
strength (TS), and pendulum impact strength (PIS) of ten different laminated patterns of RWBLCs are
displayed in Table 1.
Table 1. Static destructive mechanics and pendulum impact properties
Patterns
MOE (GPa)
MOR (MPa)
VSS (MPa)
TS (MPa)
PIS (kJ/m2)
1
2.80 ± 0.18 DE
51.73 ± 2.38 D
3.74 ± 0.22 D
43.18 ± 3.55 B
20.85 ±1.78 B
2
1.82 ± 0.14 FG
33.40 ± 1.63 F
2.40 ± 0.13 E
33.19 ± 1.67 C
21.70 ±1.41 B
3
2.42 ± 0.20 EF
29.79 ± 2.06 F
2.75 ± 0.13 E
24.37 ± 1.68 D
22.42 ± 2.41 B
4
3.84 ± 0.31 B
76.53 ± 5.01 B
5.39 ± 0.41 B
41.32 ± 3.64 B
33.06 ± 2.98 C
5
1.55 ± 0.09 GH
41.43 ± 2.11 E
2.57 ± 0.10 E
32.65 ± 2.85 C
20.26 ± 0.56 B
6
1.01 ± 0.03 H
21.71 ± 1.86 G
1.48 ± 0.08 F
16.23 ± 0.61 E
17.28 ± 1.32 A
7
3.54 ± 0.29 BCD
64.37 ± 4.95 C
4.76 ± 0.39 C
43.42 ± 4.01 B
34.89 ± 1.30 C
8
3.05 ± 0.20 CDE
67.55 ± 3.90 C
4.73 ± 0.33 C
42.52 ± 3.34 B
43.93 ± 3.21 D
9
3.57 ± 0.36 BC
53.51 ± 3.67 D
4.56 ± 0.26 C
34.86 ± 3.20 C
18.99 ± 1.73 A
10
8.41 ± 0.52 A
111.61 ± 5.96 A
7.41 ± 0.36 A
50.12 ± 4.77 A
29.99 ± 2.93 C
Note: Different capital letters indicate a significant difference (p < 0.05) in MOE, MOR, VSS, TS, and
PIS for different patterns of assembly for RWBLCs.
3.2.1 Three-point bending and shearing properties
It can be seen in Table 1 that pattern 10 possessed the highest MOE and MOR among the ten
types of laminated composites, because it was manufactured with the largest amount of wood veneers,
and the bending MOE and MOR of wood were several hundred times higher than those of rubber.
Those occupied the rest of top five in MOE and MOR value were pattern 4, 7, 8 and 9, which
possessed the similar structural design of table tennis racket (rubber sheets and biomass laminates acted
as surface and core layers, respectively). For these four kinds of RWBLCs, five layers of wood or
bamboo were compressed into a whole for load bearing, rather than relying on compressive units of
only two or three layers of wood (pattern 1, 2, 3 and 5). Besides, pattern 6 had the lowest MOE and
MOR, because the alternate arrangement of wood and rubber contributed to the failure to obtain a
wooden integral of no less than two poplar layers.
Similarly, pattern 10, 4, 7, 8 and 9 ranked in the top five in VSS, which indicated their first-class
bonding performance among ten kinds of RWBLCs, due to the largest amount of biomass bonding
interface (BBI), i.e. wood-wood, wood-bamboo, bamboo-bamboo). Through high temperature hot
pressing, wood or bamboo fibers were subject to interactive frictional compression and crosslinked
interlocking under the action of adhesive, that their pore and void spaces were filled and packed in a
relatively great degree. However, such reaction and behavior would not occur between wood and
rubber.
Table 1 shows that pattern 1 ranked sixth in VSS, due to the four discontinuous BBIs itself, rather
than four continuous ones (pattern 4, 7, 8 and 9). In addition, there was no significant difference for the
following three patterns 2, 3 and 5 in VSS. For inexistence of BBI, pattern 6 achieved the lowest VSS.
The structural design can be classified into several groups according to the amount and location of
rubber sheets (Table 2), which would be beneficial to bending failure analysis of RWBLCs (Fig. 5).
For pure wooden laminated composite (pattern 10), fibrous pull-out and stripping occurred in the
tension side, while buckling in the compression side. Fibrous pull-out, slippage and debonding could
also be observed near the core layer. For the second group (pattern 1), wood fibers were pulled out on
the bottom, which further caused interfacial debonding between secondary outer layers. The third
group of RWBLCs experienced fibrous pull-out of lower surface poplar veneer, and then wood-rubber
debonding, while an extra wood-rubber debonding for pattern 6 as load transmitted upwards. For the
fourth group, lower surface rubber sheet was stretched apart near the midpoint, and wooden fibrous
pull-out occurred at the same site in adjacent layer, with subsequent crack propagation till complete
failure. Particularly, bamboo fibrous stripping can be noticed in pattern 9, due to its sandwich layer B'
not functioning as a bend-bearing unit. The difference of failure mode between the fourth and fifth
groups of RWBLCs was that as crack extended and reached core rubber sheet, it broke off and further
overall slippage and malposition arose in pattern 5.
Table 2. Classification of different structural designs according to the amount and location of
rubber sheets
The location of rubber sheet
Group number
Pattern number
The amount of rubber sheets
As surface
As core
1
10
0
×
×
2
1
1
×
√
3
2, 3
2
×
×
4
4, 7, 8, 9
2
√
×
5
5
3
√
√
6
6
3
×
√
Fig. 5. Bending failure of RWBLCs
3.2.2 Parallel-to-grain tensile properties
As Table 1 presents, pattern 10 had the largest parallel-to-grain TS among the ten, due to its
possession of maximum plant fiber for tension, followed by pattern 1, 4, 7 and 8. The sandwich layer
B' was one bamboo bundle veneer vertical to grain direction, not acting as a load-bearing role for
parallel-to-grain tension, therefore pattern 9 was out of the top five in TS. For pattern 6, the inexistence
of BBI would not lead to meaningful friction between laminates, which made no further contribution to
tensile capacity.
3.2.3 Pendulum impact capacity
The PIS values of ten different patterns of RWBLCs, as well as related significant difference
analysis results, are displayed in Table 1. The pattern 8 achieved the highest PIS, which may be
attributed to not only the protection of surface rubber sheets (capability of energy absorption), but also
anti-shock capacity of bamboo[32]. There was no significant difference for the following three patterns
7, 4 and 10 in PIS, while pattern 9 was at the bottom of the ranking list, for its core layer B' not
functioning as a load-bearing unit upon pendulum impact. In addition, pattern 6 had the lowest PIS,
because it did not have any rigid body made of more than one wood veneer, and further the effective
defense had not been built for strike. Besides, pattern 6 had the lowest MOE and MOR, because the
alternate arrangement of wood and rubber contributed to the failure to obtain a wooden integral of no
less than two poplar layers.
3.3 Cyclic perpendicular compressive behavior
3.3.1 Cyclic perpendicular compressive behavior for different patterns of RWBLCs
3.3.1.1 Load-displacement curves
Load-displacement curves for every perpendicular compression cycle, are presented in Fig. 6. The
cyclic perpendicular compressive behavior of RWBLCs can be discussed based on the classification
rule (six groups) (Table 2).
Fig. 6. Load-displacement curves for RWBLCs
For the first three groups (pattern 10, 1, 2 and 3), the slope k in the linear region (one parameter
reflecting composites’ rigidity) of load-displacement curves, showed an increasing tendency as the
number of cycles n added. Distinct increment of k value was observed initially, which indicated that
wood densification occurred and RWBLCs’ rigidity was enhanced, as RWBLCs were compacted.
However, k value levelled off as cyclic compression proceeded, for approaching the deformation-space
threshold within the wood.
For the latter three groups (pattern 4, 9, 7, 5 and 6), the parameter k declined as cyclic loading
continued, which indicated the function of rubber’s elasticity. The rubber performed voluntary and
spontaneous deformation as the elastomer, which not only provided RWBLCs with excellent damping
aseismic performance, but protect wood and bamboo from excessive plastic deformation (Table 3). For
pattern 8 particularly, there may be some causes for that k value ascended after the first compressive
cycle, however varied indistinctively for the rest cycles. One may be that such boards enjoyed
wood/bamboo densification and buffering protection simultaneously, the other may be that they
possessed three layers of parallel-to-grain bamboo sheets in the middle, which further constituted a
damped aseismic body for reduplicative compression.
3.3.1.2 Variation in thickness
The thickness decrement of RWBLCs after ten cycles of perpendicular compression was obtained,
as Table 3 presents.
Table 3. Thickness decrement of RWBLCs after ten cycles of perpendicular compression
Decrement for wood(mm)
Decrement for bamboo(mm)
Patterns
Total
Per layer
Total
Per layer
1
0.3281 ± 0.0216
0.0547 ± 0.0036 AB
N.A.
N.A.
2
0.2535 ± 0.0223
0.0507 ± 0.0045 B
N.A.
N.A.
3
0.2418 ± 0.0192
0.0484 ± 0.0038 B
N.A.
N.A.
4
0.0999 ± 0.0081
0.0200 ± 0.0016 C
N.A.
N.A.
5
0.0431 ± 0.0033
0.0108 ± 0.0008 E
N.A.
N.A.
6
0.0466 ± 0.0031
0.0117 ± 0.0008 E
N.A.
N.A.
7
0.0601 ± 0.0029
0.0150 ± 0.0007 D
0.0201 ± 0.0009
0.0201 ± 0.0009 A
8
0.0301 ± 0.0022
0.0151 ± 0.0011 D
0.0627 ± 0.0033
0.0209 ± 0.0011 A
9
0.0318 ± 0.0006
0.0159 ± 0.0003 D
0.0528 ± 0.0030
0.0176 ± 0.0010 B
10
0.5936 ± 0.0512
0.0594 ± 0.0051 A
N.A.
N.A.
Note: Different capital letters indicate a significant difference (p < 0.05) in thickness decrement per
wood or bamboo layer, for different patterns of assembly for RWBLCs.
The first group (pattern 10) of composites were subject to the most severe contraction for its
possession of the largest amount of polyporous biomass material. Rubber sheet suffered little thickness
variation after every cycles of offloading. As for thickness decrement per wood layer, first three groups
(pattern 10, 1, 2 and 3) ranked at the top, which coincided with the above-mentioned comments that
they experienced wood densification and rigidity enhancement. The fourth group (pattern 4, 7, 8 and 9)
performed a relatively mild deformation, due to the presence of rubber sheets as “bodyguard” for the
biomass material inside. Due to the existence of the maximum damped elastomer among the ten
different types of RWBLCs, the slightest variation occurred upon pattern 5 and 6 in thickness. Besides,
as for thickness decrement per bamboo layer, pattern 7 and 8 were larger than pattern 9, which was
attributed to the assembly of parallel-to-grain fibers.
Table 4. Energy change for RWBLCs within ten cycles of compression
Energy change ΔE in a particular interval (J)
Patterns
ΔE12
ΔE23
ΔE34
ΔE45
ΔE56
ΔE67
ΔE78
ΔE89
ΔE910
1
-0.02212
-0.00366
-0.00105
-0.00198
-0.00124
-0.00137
-0.00034
-0.00103
-0.00004
2
-0.18282
-0.05643
-0.02419
-0.02381
-0.01366
-0.00793
-0.01359
-0.00493
-0.00627
3
-0.36082
-0.02960
-0.02709
-0.01482
-0.00360
-0.00810
-0.00273
-0.00299
-0.03042
4
-0.06482
0.00127
0.00199
0.00384
0.00539
0.00586
0.00265
0.00342
0.01316
5
-0.04446
0.00240
0.00757
0.00609
0.01052
0.00699
0.00973
0.00695
0.01507
6
-0.78803
-0.04589
0.00222
0.03678
0.00301
0.01388
0.01307
0.00346
0.02816
7
-0.04827
-0.00575
0.00125
0.00052
0.00112
0.00209
0.00053
0.00031
0.00052
8
-0.02924
-0.00302
0.00012
-0.00010
-0.00021
0.00043
0.00018
-0.00117
0.00069
9
-0.06788
0.00039
0.00119
0.00045
0.00025
0.00104
0.00179
0.00338
0.00288
10
-0.19000
-0.02466
-0.01029
-0.00507
-0.00518
-0.00264
-0.00368
-0.0010
-0.00129
Note: ΔEij (j＞i) represents the value of the total energy within cycle j minus that within cycle i, that is,
positive and negative value indicated energy absorption and dissipation, respectively.
3.3.1.3 Energy change
The change of energy value for RWBLCs within the whole compression, is displayed in Table 4.
It can be seen that the first three groups (pattern 10, 1, 2 and 3) of RWBLCs were subject to consistent
energy dissipation during the whole compression test, due to not only the smallest amount of the high
elastic damping rubber dampers, but the inexistence of rubber sheets acting as “bodyguard” for the
biomass material inside. As a contrast, the latter three groups (pattern 4, 7, 8, 9, 5 and 6) of boards just
experienced one or two rounds of energy dissipation initially, while energy absorption for the rest
intervals. It can be noticed in Table 4 that the fourth and fifth groups (pattern 4, 5, 7, 8 and 9) suffered
markedly lower energy dissipation than the rest groups for the first compression interval, which
indicated again the significance of cushion protection of surface rubber layers.
Synthesis of k value, thickness decrement and energy change analysis led the conclusion that the
“table tennis racket” structures (pattern 4, 5, 7, 8 and 9) achieved not only great damping aseismic
performance but above-average deformation resistance among the ten kinds of laminates in this paper.
3.3.2 Cyclic perpendicular compressive behavior under different temperature condition
3.3.2.1 Load-displacement curves
Different kinds of RWBLCs were subject to one-hour confinement at 140, 170, 200, 230, or
260°C, and then the cyclic compression. The effect of temperature condition on cyclic perpendicular
compressive behavior of three typical structures of RWBLCs (pattern 10 for group 1, pattern 1 for
group 2, and pattern 7 for group 4) are illustrated in Fig. 7.
Fig. 6 and 7 reveals that k value of pattern 10 experienced a large increment generally when
condition temperature varied from 140°C to 170 or 200°C, and a slight overall decline when it came to
230°C, which indicated that composites’ rigidity performed a parabola tendency as condition
temperature rose. For pattern 1, k value roughly diminished with the increase of temperature, and even
a great degree of buckling occurred since 230°C, illustrating its debilitated rigidity. It can be noticed
that pattern 7 achieved a very slight decline in k value, meanwhile an increase in the total displacement,
within the range from 140 to 200°C. As the temperature arrived at 230 or 260°C, the load-displacement
curve of pattern 7 for the first cycle suffered a bit of slippage or twist, which might be attributed to
micro damage of brittle curing layer of PF resin. However, it exerted little influence on the composites’
load bearing as an integrated elastomer, for the rest of cyclic perpendicular compression, which
illustrated again that such “table tennis racket” structural achieved not only great damping aseismic
performance but sound deformation resistance among the RWBLCs in this paper. Besides, the other
three groups (group 3, 5 and 6) of RWBLCs were incapable of withstanding the whole ten cycles of
perpendicular compressive loading even when it just reached 230°C.
The above-mentioned cyclic perpendicular compressive behavior of different RWBLCs varied as
the condition temperature rose, which should be related with the effect of temperature on chemical
composition of the biomass material (wood and bamboo), rather than rubber within the variation range
of temperature in this study[33].
Fig. 7. Load-displacement curves for RWBLCs under different temperature condition
3.3.2.2 Chemical component variation
Fig. 8 provides the representative infrared spectra of wood and bamboo powders treated on
different temperature conditions (140, 170, 200, 230, or 260°C).
Fig. 8. Representative infrared spectra of wood and bamboo powders treated on different
temperature conditions
For wood powder, the absorbance at 1800~1700 cm-1 disappeared at 260°C, which indicated the
vanishment of carbonyl stretching of the unconjugated β-ketone and conjugated acid/esters (-C=O- and
-C=C-). The deletion of such chemical functional groups was probably attributed to the condensation
reactions of lignin and deacetylation of hemicelluloses[34].
For bamboo powders, the absorbance at 1800~1700 cm-1 disappeared when it just reached 230°C,
which indicated that the degradation of hemicelluloses and lignin occurred earlier than wood under
high-temperature treatment. Besides, the loss of absorption peak at 880~850 cm-1 implied the
decomposition of cellulose at 230°C. The hydrogen bonded O-H stretching around 3400 cm-1 was
invisible at 260°C, illustrating the decrease of lignin and cellulose. Besides, synthesis of the invisibility
of absorption peaks at 2950~2900, 1500~1150, 1020~1000, 880~850 cm-1 led to the conclusion that
bamboo suffered a large degree of pyrogenic decomposition of cellulose.
3.3.2.3 Variation in degree of crystallinity
The XRD patterns of wood and bamboo powders treated on different temperature conditions (Fig.
9) shows two peaks representing the planes 101 and 002 at 2θ around 16º and 22º respectively
(characteristics of cellulose I crystalline phase of wood and bamboo), in accordance with other
literature[35]. As condition temperature varied from 140 to 260°C, the degree of crystallinity achieved
17.06%, 19.05%, 22.09%, 19.20% and 15.03%, respectively. In initial stage of temperature rise, the
escape of bound water made microfibrils closer that more hydrogen bonding was generated, i. e. a
larger degree of crystallinity was obtained[2]. As it exceeded a certain temperature limit (around
200°C), the proportion of crystalline region started to decrease due to the occurrence of cellulose
degradation[36], which agreed with the findings mentioned above in the section 3.3.2.2).
Fig. 9. XRD spectra of wood and bamboo powders treated on different temperature conditions
The degree of crystallinity of bamboo powder increased (19.14%, 20.58%, 21.96%) with the
elevated temperature (140, 170, 200°C) first, whereas experienced a dramatic drop to 8.53% at 230°C
corresponding to the start of cellulose decomposition. When it came to 260°C, the peaks at 2θ around
16º and 22º could not be observed that the vast majority of cellulose had been decomposed, which
coincided with the infrared spectra and corresponding explanation in the above section 3.3.2.2).
3.3.2.4 Microstructure-scale compressive deformation illustration
The variation in chemical functional groups and the degree of crystallinity implied the vanishment
of substance functioned as skeleton and incrustation that bamboo suffered severe invalidation of
mechanical bearing units at 260°C, which responded its deformation and even crack generation within
cyclic compression (seen in the last image of Fig. 7).
4 Conclusions
Inspired by the structure of table tennis racket, the concept of rubber-wood-bamboo laminated
composites (RWBLC) was raised, seeking for the possibility of rubber playing the role of “bodyguard”
for wood and bamboo, for better performance in certain areas.
(1) The addition of rubber increased RWBLCs’ density (0.67~0.92 g·cm-3), which exerted little
influence on the lightweight design of biomass based composites in construction and transportation
area.
(2) The RWBLCs with similar structural design of table tennis racket (rubber sheets and biomass
laminates acted as surface and core layers, respectively, i. e. RPPPPPR, RPPBPPR, RPBBBPR, had
superior three-point bending, shearing, and pendulum impact capacity. Particularly, RPPPPPR,
RPPRPPR, RPPBPPR, RPBBBPR, RPBB'BPR achieved not only great damping aseismic performance
but above-average deformation resistance among the ten kinds of laminates in this paper.
(3) Condition temperature variation led to chemical component and microstructure change of
biomass material (wood and bamboo), which further had marked influence on cyclic perpendicular
compressive behavior of RWBLCs. As environment temperature increased from 140°C to 260°C,
wood and bamboo performed a parabola tendency (first slight rise within 140~200°C and then distinct
fall within 230~260°C) in the degree of crystallinity. The pyrogenic decomposition of cellulose and
lignin was observed around 260°C that RWBLCs could not bear the whole ten cycles of perpendicular
compressive loading, except pattern 7 (RPPBPPR).
Acknowledgments: This work was supported by Fundamental Research Funds of International Center
for Bamboo and Rattan [1632019003]; China Postdoctoral Science Foundation [2019M660500].
Author Contributions: Materials preparation: Jianchao Deng and Xin Wei; Experimental design:
Jianchao Deng, Xin Wei, Shuangbao Zhang; Data collection, analysis and interpretation: Jianchao
Deng, Haiying Zhou, Xin Wei; Manuscript writing: Jianchao Deng; Project administration: Ge Wang,
Declarations of interest: None.
“Data Availability” statement: All the authors promise that the data in this paper are real and
effective. Research data referred in the article have all been correctly cited in the following reference
section.
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Highlights
★ Rubber played the role of “bodyguard” for biomass material within
rubber-wood-bamboo hybrid laminated composite (RWBLC).
★ The structural design of table tennis racket provided RWBLCs with great damping
aseismic performance and superior deformation resistance.
★ Bamboo suffered more severe invalidation of mechanical bearing units than wood
at 260°C.
★ RWBLCs could not bear the whole ten cycles of perpendicular compressive loading
at 260°C, except the RPPBPPR ones.
Graphical Abstract
Declaration of interests
☒ The authors declare that they have no known competing financial interests or
personal relationships that could have appeared to influence the work reported in
this paper.
☐The authors declare the following financial interests/personal relationships
which may be considered as potential competing interests:
Author Contributions:
Jianchao Deng: Materials preparation, Experimental design, Data collection, analysis and
interpretation, Manuscript writing
Xin Wei: Materials preparation, Experimental design, Data collection, analysis and interpretation
Haiying Zhou: Data collection, analysis and interpretation
Ge Wang: Experimental design, Project administration
Shuangbao Zhang: Experimental design
