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Internal bonding strength test of medium density board and particleboard

Internal bonding strength test of medium density board and particleboard

Release date: May 14, 2022 browse: 1164 times

Abstract: using hot melt adhesive as adhesive, the inner bonding strength test specimens of density board / particleboard were bonded. The effects of different metal clip temperatures (50 ℃, 70 ℃, 90 ℃, 110 ℃, 130 ℃ and 150 ℃) on the inner bonding strength test results were studied. The results show that the bonding strength of MDF / particleboard increases first and then decreases with the increase of temperature; When the temperature is 50 ℃, the bonding between the specimen and the metal clamp is not firm, and the measured value of internal bonding strength is low; When the temperature is 70 ℃ and 90 ℃, there is little difference in the measured value of internal bonding strength, and the measured value of internal bonding strength is at the highest; When the temperature is 110 ℃, 130 ℃ and 150 ℃, the measured value of internal bonding strength decreases significantly, and the downward trend of thin plate is more obvious than that of thick plate. Therefore, it is suggested that when testing the bonding strength of wood-based panels, the temperature of the metal clip when bonding the metal clip and the test piece should be controlled at 70 ~ 90 ℃.

Density board / particleboard is made of wood fiber / particleboard by hot pressing with adhesive. The bonding degree of fiber, particleboard and adhesive can be characterized by the size of internal bonding strength. Therefore, internal bonding strength is one of the main indicators to measure the physical and chemical properties of density board / particleboard . In the actual inspection process, the internal bonding strength is the inspection item with a high unqualified rate in the quality inspection of density board / particleboard products. Through a large number of practical tests, it is found that the test value of internal bonding strength is closely related to the metal clip temperature (hereinafter referred to as the bonding temperature) when bonding the metal clip and the test piece during the manufacturing process of the test piece. Too high bonding temperature is easy to damage the internal structure of MDF / particleboard, and too low is not conducive to stable bonding. However, gb/t 17657-2013 “test methods for physical and chemical properties of wood-based panels and veneered wood-based panels” does not make specific provisions on this parameter, so different testers or institutions often have different test results on the internal bonding strength of the same MDF / particleboard products.

Therefore, the author takes medium density board, particleboard, veneered density board and veneered particleboard as the research object. Under the condition of keeping other conditions unchanged, by changing the bonding temperature when the specimen is made, the author explores its influence on the internal bonding strength test results, in order to determine the appropriate bonding temperature and provide reference for peer inspection and standard formulation and revision.

1 materials and methods

1.1 materials

1) Density board / particleboard internal bonding strength test specimen.

In order to reduce the impact of differences in the type and thickness of wood-based panels on the test results, a total of 4 kinds of wood-based panels, including medium density board, particleboard, decorative density board and decorative particleboard, were selected in this test, and each kind of panel was selected as thick and thin, with a total size of 2440 mm × 1220 mm, 8 wood-based panels with relatively uniform performance were placed in an environment with a temperature of (20 ± 2) ℃ and a relative humidity of (65 ± 5)% for 7 days. See Table 1 for the measured values of thickness, density and moisture content of 8 wood-based panel test panels. The relative deviation of measured values in the panels is less than 5%.

After 100 mm of each large plate is cut, the specification is (50 ± 1) mm in turn with a precision sliding table saw × There are 36 internal bonding strength test specimens (50 ± 1) mm, and the distance between individual specimens is not less than 100 mm. During the preparation process, the test pieces with appearance defects shall be removed and re prepared. After the preparation of the test piece, place it in a constant temperature and humidity chamber with a temperature of (20 ± 2) ℃ and a relative humidity of (65 ± 5)% to achieve a constant mass (the difference between the two weighing results at an interval of 24 hours does not exceed 0.1% of the mass of the test piece).

2) Hot melt adhesive stick (EVA): melting point 100 ℃, curing time 8 ~ 15 s, purchased.

Table 1 Parameters of density board / particleboard test panel

number type Thickness / mm Density / (g/cm3) Moisture content /%

MDF1 Medium density fiberboard sheet five point eight zero point seven one six point six

MDF2 Medium density fiberboard thick board eighteen zero point seven one six point seven

PB1 Particleboard sheet six zero point six eight seven

PB2 Particleboard thick board eighteen zero point six eight seven

SMDF1 Veneer fiberboard sheet five point eight zero point seven two six point eight

SMDF2 Veneer fiberboard thick board eighteen zero point seven two six point eight

SPB1 Veneer particleboard sheet six zero point six seven seven

SPB2 Veneer particleboard thick board eighteen zero point six seven seven

1.2 equipment

Microcomputer controlled electronic universal tensile testing machine: model cmt-6503, measuring range 0 ~ 5000 n, Shenzhen xinsansi material testing Co., Ltd; Oven: model dhg-9145a, Shanghai Yiheng Scientific Instrument Co., Ltd; Electronic digital caliper: measuring range 0 ~ 200 mm, Chengdu Chengliang Tools Co., Ltd; Metal clip: customized, bonding area 50 mm × 50 mm。

1.3 test design

According to the previous test, six bonding temperatures of 50 ℃, 70 ℃, 90 ℃, 110 ℃, 130 ℃ and 150 ℃ were selected. Six specimens were tested for each plate at each temperature. The arithmetic mean of the bonding strength test values in the six specimens was taken as the measured value at the corresponding temperature of the plate. Because it is difficult to accurately control the temperature of the adhesive layer during the detection process, in order to keep the temperature constant to the greatest extent, the metal chuck is placed in the constant temperature drying oven for more than 1 hour and kept for 5 minutes after gluing, so as to make the temperature of the adhesive layer reach the set gluing temperature as much as possible.

1.4 performance test

Measure the internal bonding strength according to the method specified in gb/t 17657-2013. When the metal chuck is taken out of the drying oven at the set temperature, bond the test piece and the chuck together immediately. After one side is cured, bond the other side with the same method, and then place the glued assembly at room temperature for natural cooling for 1 ~ 2 hours before testing. According to the relevant research conclusions , in order to ensure the comparability of the test results, the same universal joint is used in the test process, and the load is uniformly loaded at the loading speed of 1.5 mm / min.

2 results and analysis

2.1 internal bonding strength of MDF samples

The internal bonding strength test results of MDF samples at different bonding temperatures are shown in Figure 1.

It can be seen from Figure 1 that the internal bonding strength of MDF increases first and then decreases with the increase of bonding temperature. When the temperature is 70 ℃, the internal bonding strength test values of both thin plate (mdf1) and thick plate (mdf2) reach the maximum value. When the temperature rises to 150 ℃, the internal bonding strength of thin plate decreases by 45%, and the internal bonding strength of thick plate decreases by 38%.

When the bonding temperature is 50 ℃, the test value of the internal bonding strength of the MDF is relatively low, because at this bonding temperature, the hot melt adhesive has not been completely melted, the fluidity of the adhesive layer is poor, the test piece and the metal chuck cannot be well bonded together, and the corner is prone to lack of adhesive. When testing, the test piece is often not pulled away from the middle, but destroyed from the corner.

When the bonding temperature is 90 ℃, the internal bonding strength of MDF thin plate is slightly lower than that of 70 ℃, while the internal bonding strength of thick plate remains unchanged, indicating that between these two temperature ranges, the internal bonding strength test results of MDF are not affected by the bonding temperature.

When the bonding temperature rises from 90 ℃ to 130 ℃, the internal bonding strength of MDF decreases significantly, and the decline of thin plate is greater than that of thick plate, indicating that the bonding temperature at this time has the greatest impact on the internal bonding strength test results of MDF, and the impact on thin plate is greater than that of thick plate. With the increase of the bonding temperature, the moisture inside the MDF evaporates rapidly, and the stress becomes larger. At high temperature, the urea formaldehyde resin in the specimen solidifies and becomes brittle, and the wood fiber also has the trend of shrinkage and carbonization, which reduces the bonding strength between the fibers and reduces the internal bonding strength value. The thinner the specimen, the greater the thermal effect, and the greater the impact.

When the bonding temperature rises from 130 ℃ to 150 ℃, the decline of the internal bonding strength test value of the medium density board is basically unchanged, indicating that the effect of the bonding temperature on the internal bonding strength of the medium density board is not different at this time. It can be inferred that when the temperature is 130 ℃, the interior of the specimen may have been destroyed.

2.2 internal bonding strength of particleboard samples

The internal bonding strength test results of particleboard samples at different bonding temperatures are shown in Figure 2.

It can be seen from Figure 2 that the change law of the internal bonding strength test results of particleboard with the increase of bonding temperature is basically consistent with that of medium density board, and the overall trend is to rise first and then fall. When the temperature rises to 150 ℃, the internal bonding strength test value of Particleboard thin plate (PB1) decreases by 43%, and the internal bonding strength of particleboard thick plate (Pb2) decreases by 34%. It is found that with the increase of bonding temperature, the decrease of bonding strength test value in particleboard is lower than that of medium density board, whether it is thin or thick, which is determined by the loose and porous internal structure of particleboard. Heat conduction is not easy to occur at high temperature, and the degree of internal structure damage is relatively small.

2.3 internal bonding strength of decorative panel samples

The internal bonding strength test results of veneered density board samples and veneered particleboard at different bonding temperatures are shown in Figure 3 and Figure 4.

It can be seen from Figure 3 and Figure 4 that the change law of the internal bonding strength test results of veneered density board and veneered particleboard with the increase of bonding temperature is consistent with the change law of MDF and particleboard samples discussed previously. With the increase of bonding temperature, the internal bonding strength test results first increase and then decrease. When the temperature rises to 150 ℃, the internal bonding strength test value of veneered density board sheet (smdf1) decreases by 42%, Smdf2, spb1 and spb2 decreased by 36%, 40% and 33% respectively. Through comparison, it is found that no matter the density board or particleboard, the decline of the internal bonding strength after finishing is lower than that of the test results of the internal bonding strength of the plain board, which may have a certain relationship with the finishing material. The finishing material blocks the base material from the hot melt adhesive and reduces the damage of high temperature to the base material structure.

3 conclusions and suggestions

The test value of inner bond strength of density board / particleboard shows a trend of first rising and then falling with the increase of metal clamp temperature during bonding. When the temperature rises to 150 ℃, the test result of inner bond strength of thin plate decreases by 40% – 45%, and that of thick plate decreases by 33% – 39%. When the temperature is 50 ℃, the internal bonding strength test results are generally relatively low, and at this time, the specimen is not firmly bonded to the metal clip; When the temperature is 70 ℃ and 90 ℃, there is little difference in the measured value of internal bonding strength, which is basically the highest; When the temperature is from 90 ℃ to 130 ℃, the measured value of the internal bonding strength decreases significantly, and the decrease range of the thin plate is greater than that of the thick plate. At this time, the temperature has the greatest impact on the internal bonding strength, and the impact of the thin plate is greater than that of the thick plate; When the temperature rises from 130 ℃ to 150 ℃, the influence of temperature on the measured value of internal bonding strength is not significant. Considering comprehensively, it is suggested that the temperature of the metal chuck should be controlled at 70 ~ 90 ℃ when the specimen is cemented with the chuck.

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