Interfacial bonding properties of multi-phase co-extruded wood-plastic composites
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摘要: 针对新型多元共挤出复合材料存在的次表层木塑复合材料(WPCs)与核层实木界面结合强度低,使用过程中易发生界面剥离导致复合材料力学性能和使用寿命降低的问题,本文采用聚氨酯热熔胶胶膜(TPU)和乙烯-丙烯酸共聚物胶膜(EAA)包覆单板层积材(LVL)与塑料/木塑制备了高界面结合强度的多元共挤出复合材料(Co-WPCs-LVL)。研究结果表明:TPU和EAA均能有效提高WPCs层与核层LVL的界面结合强度,界面结合强度随着胶膜熔点的增加而逐渐降低,其中引入TPU (熔点80℃)和EAA (熔点95℃)的WPCs与LVL界面结合强度相对于未处理组分别提高了27倍、56倍。EAA可以显著提升WPCs与LVL的界面耐水性能,Ⅱ类浸渍实验后界面未发生剥离。证明胶膜在高温的挤出作用下能够渗入LVL表面与羟基(—OH)发生反应,同时能与聚乙烯分子链混合扩散形成牢固的界面结合。经过人工加速老化后,胶膜处理组的WPCs与LVL仍具有较高的界面结合强度,界面结合强度剩余率随着熔点的增大而增大,其中EAA(熔点135℃)实验组表现出最好的界面耐久性,界面结合强度剩余率达到97.25%。Abstract: To address the problems of low interfacial bonding strength between sub-surface wood-plastic composites (WPCs) and solid wood in the core layer of new multi-phase co-extruded composites and easy interfacial peeling in the process of use leading to the reduction of the mechanical properties and service life of the composites, this paper adopts a polyurethane hot-melt adhesive film (TPU) and an ethylene acrylic acid copolymer adhesive film (EAA) to wrap veneer laminated lumber (LVL) with plastic/wood-plastic. Multi-co-extruded composites (Co-WPCs-LVL) with high interfacial bond strength were prepared. The results showed that both TPU and EAA could effectively improve the interfacial bonding strength between WPCs layer and core layer LVL, and the interfacial bonding strength decreased gradually with the increase of the melting point of the adhesive film, among which, the interfacial bonding strength between WPCs and LVL introduced with TPU (melting point of 80℃) and EAA (melting point of 95℃) was increased by 27 and 56 times, respectively, relative to that of the untreated group. The EAA could significantly increase the interfacial bonding strength of the water resistance of the interface between WPCs and LVL, and the interface did not peel off after the Type II impregnation experiment. It proves that the adhesive film can penetrate into the surface of LVL and react with hydroxyl group (-OH) under the extrusion at high temperature, and at the same time, it can mix and diffuse with the molecular chain of polyethylene to form a strong interfacial bond. After artificially accelerated aging, the WPCs and LVL in the adhesive film treatment group still had high interfacial bonding strength, and the residual rate of interfacial bonding strength increased with the increase of melting point, among which the experimental group of EAA (melting point of 135℃) showed the best interfacial durability, and the residual rate of interfacial bonding strength reached 97.25%.
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图 4 不同试件WPCs与LVL界面结合强度测试后木破率(a) Control;(b) TPU-80;(c) TPU-100;(d) TPU-120;(e) TPU-140;(f)EAA-95;(g) EAA-115;(h) EAA-135
Figure 4. Wood failure ratio of different specimens after WPCs and LVL interfacial bond strength test (a) Control; (b) TPU-80; (c) TPU-100; (d) TPU-140; (e) TPU-140; (f) EAA-95; (g) EAA-115; (h) EAA-13
图 8 不同试件的胶膜渗入LVL的截面图像(a) Control;(b) TPU-80;(c) TPU-100;(d) TPU-120;(e) TPU-140;(f) EAA-95;(g) EAA-115;(h) EAA-135
Figure 8. Cross-sectional images of adhesive film infiltrated into LVL for different specimens (a) Control; (b) TPU-80; (c) TPU-100; (d) TPU-120; (e) TPU-140; (f) EAA-95; (g) EAA-115; (h) EAA-135
图 10 不同Co-WPCs-LVL试件Ⅱ类浸渍剥离强度测试表面形貌(a) Control;(b) TPU-80;(c) TPU-100;(d) TPU-120;(e) TPU-140;(f) EAA-95;(g) EAA-115;(h) EAA-135
Figure 10. Surface morphology of different Co-WPCs-LVL specimens tested for peel strength by Type II impregnation (a) Control; (b) TPU-80; (c) TPU-100; (d) TPU-120; (e) TPU-140; (f) EAA-95; (g) EAA-115; (h) EAA-135
表 1 不同Co-WPCs-LVL试件的组成
Table 1. Composition of different Co-WPCs-LVL specimens
Sample Surface layer WPCs layer Adhesive film layer Core layer PE-RT/
wt%SEBS/
wt%Additive/
wt%HDPE/
wt%LDPE/
wt%BF/
wt%Additive/
wt%Type Thickness/mm Melting
Point/℃Solid
WoodCtrl 80 10 10 20 5 65 10 - - - LVL TPU-80 80 10 10 20 5 65 10 TPU 0.08 80 LVL TPU-100 80 10 10 20 5 65 10 TPU 0.08 100 LVL TPU-120 80 10 10 20 5 65 10 TPU 0.08 120 LVL TPU-140 80 10 10 20 5 65 10 TPU 0.08 140 LVL EAA-95 80 10 10 20 5 65 10 EAA 0.08 95 LVL EAA-115 80 10 10 20 5 65 10 EAA 0.08 115 LVL EAA-135 80 10 10 20 5 65 10 EAA 0.08 135 LVL Notes: In the Sample column of the table, WPCs means wood-plastic composites, LVL means laminated veneer lumber, TPU means polyurethane hot melt adhesive film, EAA means ethylene acrylic acid copolymer adhesive film, and the number connected to the back represents the melting point of the adhesive film. For example: TPU-80 means that the LVL surface of Co-WPCs-LVL specimen is covered with polyurethane hot melt adhesive film with a melting point of 80℃. 表 2 不同Co-WPCs-LVL 试样的Ⅱ类浸渍剥离长度
Table 2. Type Ⅱ impregnation peeling length of different Co-WPCs-LVL samples
Sample Ctrl TPU-80 TPU-100 TPU-120 TPU-140 EAA-95 EAA-115 EAA-135 Length of impregnation
and peeling/mm300 256 235 242 238 0 0 0 表 3 不同Co-WPCs-LVL试样的Ⅰ浸渍剥离长度
Table 3. Type Ⅰ impregnation peeling length of different Co-WPCs-LVL samples
Sample EAA-95 EAA-115 EAA-135 Length of impregnation
and peeling/mm300 276 0 -
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