外文翻译--木纤维增强聚丙烯复合材料--压缩和注塑成型工艺 英文版.pdf

POLYMER PLASTICS TECHNOLOGY AND ENGINEERING Vol 43 No 3 pp 871 888 2004 Wood Fiber Reinforced Polypropylene Composites Compression and Injection Molding Process Andrzej K Bledzki and Omar Faruk Institut fu r Werkstofftechnik Kunststoff und Recyclingtechnik University of Kassel Kassel Germany ABSTRACT Wood fiber reinforced polypropylene composites containing differ ent types of wood fiber hard and softwood fiber were prepared by an injection molding and a compression molding process Influence of different processing systems and compatibilizer on the composite mechanical properties was investigated The present study investi gated the tensile flexural charpy impact and impact properties of wood fiber reinforced polypropylene composites as a function of processing system and compatibilizer From the results it is observed that injection molding process showed better tensile and flexural properties comparative with compression molding process which is about 155 and 60 for tensile strength and flexural strength Correspondence Andrzej K Bledzki Institut fu r Werkstofftechnik Kunststoff und Recyclingtechnik University of Kassel Mo nchebergstr 3 D 34109 Kassel Germany Fax 49 561 8043692 E mail kutech uni kassel de 871 DOI 10 1081 PPT 1200380680360 2559 Print 1525 6111 Online Copyright Injectionmolding Compression molding Mechanical properties INTRODUCTION Polypropylene wood fiber composites are used as substitutes for more expensive and less environmentally friendly materials Polypropyl ene is a recyclable polymer and wood fibers derive from a renewable source and are biodegradable The use of wood fibers in a polypropylene matrix includes many benefits such as improved dimensional stability of composites lower processing temperatures increased heat deflection temperature improved wood surface appearance lighter products low volumetric cost up to 30 reduced cycle time for injection molded products and production of good performance materials 1 Recent progress in compounding technology improves their compe titiveness against conventional reinforcing agents such as glass fibers and mineral particles Wood flour fillers are readily available by grinding of wood As a function of the grinding processes it is possible to control size size distribution shape and the aspect ratio of wood flour particles Typically wood flour comprises a mixture of broken fibers partially fibrillated fibers and fiber bundles Compounding wood flour together with polypropylene can afford an attractive combination of high specific stiffness and strength less abrasion during processing low density and low price with respect to mineral fillers Injection molding and extrusion are established processes for manufacturing wood fiber thermoplastic composites in prismatic or sheet forms Injection molding requires a polymer with a low molecular weight to maintain low viscosity Johnson Controls Automotive 2 presented a overview of the state of the art of the use of plastic natural fiber composite materials for interior car parts and the technologies to 872Bledzki and Faruk ORDER REPRINTS producesuchparts injectionmolding lowpressureinjectionmolding and co injection molding With emphasis on the research lines performed on several kinds of natural and wood fibers jute flax kenaf eucalyptus to be applied to semi finished products granules short natural fiber for injection molding process The properties of natural flax fiber 3 4 hemp 5 jute 6 rice hull 7 and sisal fiber 8 9 and wood fiber 10 reinforced polymer composites were investigated by the injection molding process Thermoplastic fiber reinforced composites are distinguished from thermoset reinforced composites primarily by a high elongation at break short cycle times and the possibility of recycling The compression molding technique proved suitable for the production of profiles with any thermoplastic prepreg used Compression molding brings the thermo plastic prepreg gently to the required shape without overcompressing the material The different layer orientations are thus retained after molding Johnson Controls 11 compared new materials and processes for the manufacture of automotive door panels The material is Fibropur a natural fiber mat flax sisal hemp kenaf sprayed with PU resin produced by compression molding Flax fiber 12 14 wood fiber 15 and jute fiber 16 reinforced compo sites also were prepared by compression molding process A recent review report 17 describes the reinforcement of natural and wood fibers into polymer considering different processing systems extru sion injection molding compression molding mixer and express process An important feature of the compounding processes is the addition of compatibilizers which are required to overcome incompatibility between the polar wood and the nonpolar hydrocarbon polymer Inadequate compatibility frequently is accompanied by significantly reduced impact and tensile strength The objective of these studies is to compare the mechanical properties of wood fiber PP composites between the injection molding and the compression molding process EXPERIMENTAL Materials Polymeric Matrix Polypropylene Stamylan P17M10 was provided as granules by DSM Gelsenkirchen Germany Its melting temperature was 173 C and Wood Fiber Reinforced Polypropylene Composites873 ORDER REPRINTS meltingindexwas10 5g 10minat230 C Itsdensityatroom temperature was 0 905g cm3 Wood Fibers Standard hard wood fiber Lignocel HBS 150 500 and soft wood fiber Lignocel BK 40 90 with particle size of 150 500mm were supplied by J Rettenmaier and So hne GmbH Co Germany It is also notable that fiber structure of hard and soft wood fiber is fibrous and cubic respectively Compatibilizer A commercially available maleic anhydride polypropylene copoly mer Licomont AR 504 FG was used as a compatibilizer for fiber treatment and it was obtained from Clariant Corp Frankfurt Germany It was used 5 by weight relative to the wood fiber content and was expected to improve the compatibility and adhesion between the wood fiber and the PP matrix Compounding and Sample Preparation Injection Molding Process Polypropylene granules with hard wood fiber and soft wood fiber 30 and 50 by weight were mixed by twin screw extruder Haake extruder Rheomex PTW 25 32 with and without compatibilizer All the wood fibers were initially dried at 80 C in an air circulating oven for 24hr before mixing The extruded granules were dried again 80 C for 24hr water content 1 before the sample preparation by the injection molding process Test samples were prepared from dried granules by the injection molding process at melting temperature 150 C 180 C mold temperature of 80 C 100 C and under a injection pressure 20kN mm2 Compression Molding Process Polypropylene granules were converted into powder and then mixed with wood fibers The wood fiber and PP powder mixture were placed 874Bledzki and Faruk ORDER REPRINTS into a block cylinder compression molding machine under a pressure 20kN mm2till the temperature reached at 190 C Then the cylinder pressed for 5min under a pressure 20kN mm2 and then it was followed by cooling 10 C min in another press equipped with refrigeration facilities The prepared sheet 7mm then was placed into a compression molding machine at 180 C for 5 10min under a pressure 3kN cm2to bring the sheet to a 2mm thickness Rectangular specimens were cut from the pressed sheets according to a DIN number for various mechanical experiments Measurements The tensile and flexural strength Zwick Machine UPM 1446 were tested at a test speed of 2mm min according to EN ISO 527 and EN ISO 178 for different wood fiber PP composites with and without a com patibilizer in both processes All the tests were investigated at room temperature 23 C and at a relative humidity of 50 A charpy impact test EN ISO 179 was carried out with 10 unnotched samples In each series standard deviation 15 was used to measure charpy impact energy To measure the impact characteristics values the specimens were tested by using a low velocity falling weight impact tester EN ISO 6603 2 at room temperature in nonpenetration mode The impactor had a mass of 0 75kg and the impact energy was 0 96J Scanning Election Microscope The morphology of the wood fiber PP composites prepared in both processes were investigated by using a scanning electron microscope SEM VEGA TESCAN whereas fractured surfaces of flexural test samples were studied with SEM after being sputter coated with gold RESULTS AND DISCUSSION Wood fiber PP composites with 30 and 50wt of fiber loading were prepared to investigate the effect of processing systems on mechanical properties like tensile and flexural strength flexural E modulus charpy impact strength and impact properties of composites We have repor ted 18 earlier that wood fiber PP composites containing MAH PP Wood Fiber Reinforced Polypropylene Composites875 ORDER REPRINTS compatibilizer showed the best performance in the concentration of 5 relative to the wood fiber content That is why in our present work the content of MAH PP was used at 5 for all types of wood fiber PP composites in both processes The various properties of these composites are discussed below Results of tensile test of the wood fiber PP composites are shown in Fig 1 with the variation of wood fiber hard wood fiber and soft wood fiber and with and without a compatibilizer for both processes In general the wood fiber PP composites show an increasing trend in the mechanical properties with the addition of a compatibilizer Figure 1 showed that the tensile strength of the composites prepared by the injection molding process is higher compared to the composites prepared by the compression molding process and it also illustrated that hard wood fiber reinforced PP composites prepared by the injection molding process showed highest tensile strength with the addition of a com patibilizer which is nearly at 155 increase to the compression molding process at the 50 wood fiber content The effect of a processing system on the flexural properties of wood fiber PP composites can be readily assessed from the Figs 2 and 3 It is observed that the flexural strength Fig 2 of the composites showed an 0 5 10 15 20 25 30 35 40 WF30 WF30 MAH PP5 WF50 WF50 MAH PP5 HW injection molding HW compression molding SW injection molding SW compression molding Tensile strength MPa Figure 1 Tensile strength of hard and soft wood fiber PP composites with and without compatibilizer in both processes View this art in color at 876Bledzki and Faruk ORDER REPRINTS 0 10 20 30 40 50 60 70 WF30 WF30 MAH PP5 WF50 WF50 MAH PP5 HW injection molding HW compression molding SW injection molding SW compression molding Flexural strength MPa Figure 2 Flexural strength of hard and soft wood fiber PP composites with and without compatibilizer in both processes View this art in color at 0 1 2 3 4 5 6 WF30 WF30 MAH PP5 WF50 WF50 MAH PP5 HW injection molding HW compression molding SW injection molding SW compression molding Flexural E modulus GPa Figure 3 Flexural E modulus of hard and soft wood fiber PP composites with and without compatibilizer in both processes View this art in color at Wood Fiber Reinforced Polypropylene Composites877 ORDER REPRINTS increasing tendency with the addition of a compatibilizer With the comparison between both processing systems at the 30 wood fiber content both hard wood fiber and soft wood fiber it is not a very significant difference But at the 50 wood fiber content the injection molding process showed better flexural strength with an increase about 60 to compression molding process Figure 3 showed that the flexural E modulus of the hard wood fiber and soft wood fiber PP composites in both processing system followed the same trend as flexural strength It means at the 30 wood fiber content both hard wood fiber and soft wood fiber it is not very significant in difference But at the 50 wood fiber content the injection molding process showed better flexural strength with an increasing tendency to the compression molding process Figure 4 shows the variation of charpy impact strength of wood fiber PP composites in both processes with the addition of a com patibilizer From the figures it is seen that the charpy impact strength of the hardwood fiber and soft wood fiber PP composites are found to be more prepared by the compression molding process than by the injection molding process With the addition of compatibilizer in com posites charpy impact strength increased the maximum in the compres sion molding process for hard wood fiber PP composites and it is about 70 at the wood fiber content 30 The results of the impact test can be described by two separate issues described in Fig 5 They are a Force deflection curve the force deflection curve refers to all the materials behaviors including the damage initiation defined by the first significant drop of the force b Characteristic values loss energy Wv as a measure of dissipated energy and strain energy Ws as a measure of the stored energy and the damping index as a ratio of loss energy to strain energy Impact resistance of hard wood fiber and soft wood fiber PP composites in both processes is shown in Fig 6 Figure 6a illustrated the impact resistance of hard wood fiber PP composites with and without a compatibilizer in both processes and impact resistance in the injection molding process shows better performance where in the compression molding process a large amount of damage of initiation was observed But with the addition of a compatibilizer impact resistance of hard wood fiber PP composites shows highest performance in the compression molding process without having a large amount of damage of initiation In the case of soft wood fiber PP composites Fig 6b it is 878Bledzki and Faruk ORDER REPRINTS clearly observed that impact resistance in the injection molding process shows the better performance comparative to the compression molding process without having a large amount of damage of initiation as with the compression molding process a b 0 2 4 6 8 10 12 14 Charpy impact strength mJ mm2 Injection moldingCompression molding 0 2 4 6 8 10 12 14 Charpy impact strength mJ mm2 Injection moldingCompression molding SW30 PP70 SW30 PP70 MAH PP5 SW50 PP50 SW50 PP50 MAH PP5 HW30 PP70 HW30 PP70 MAH PP5 HW50 PP50 HW50 PP50 MAH PP5 Figure 4 Charpy impact strength of hard wood fiber PP composites a and soft wood fiber PP composites b with and without compatibilizer in both processes View this art in color at Wood Fiber Reinforced Polypropylene Composites879 ORDER REPRINTS The damping index for all samples was calculated by taking the ratio of dissipated energy loss energy to the stored energy strain energy to measure the impact characteristic values The loss energy involves energy that is based on irreversible deformations energy dissipation due to the creation of matrix cracks and their propagation delaminations and finally fiber fracture The damping index of hard and soft wood fiber PP composites as a function of having a compatibilizer in both processes is shown in Fig 7 It is seen that the damping index in the injection molding process is comparatively better than the compression molding process but this is not very significant It is clearly evident that more damping index is decreased with the addition of a compatibilizer in all cases and it is highest for hard wood fiber PP composites Fig 7a in the injection molding process at the wood fiber content 50 which is nearly 60 The flexural fractured surface of wood fiber PP composites in both injection and compression molding processes examined with SEM are presented in Figs 8 10 Figure 8a b shows the hard and soft wood fiber PPcompositescontaining30 woodfibercontentinthe compression molding process Both Figs 8a and 8b show the hard and soft wood fiber PP composites in the compression molding process where present fiber pullout debonding fibrillation and just like a layer to layer As we know these structures layer to layer are responsible for higher charpy impact strength and we observed that at Fig 4 where composites made from the compression molding process showed Deflection Force loss energy Wv strain energy Ws damage initiation Figure 5 Typical impact force deflection curve for fiber reinforced polymer composites including definition of the characteristic values used 880Bledzki and Faruk ORDER REPRINTS better charpy strength in comparison with injection molding process composites But with the addition of a compatibilizer indicates much better interaction between the wood fiber and the matrix in both processing systems which is represented in Figs 9 and 10 Figures 9a and 9b a b 100 0 100 200 300 400 500 600 700 01234567 Deflection mm Force N HW30 Injection molding Hw30 MAH PP5 Injection molding HW30 Compression molding HW30 MAH PP5 Compression molding 100 0 100 200 300 400 500 600 700 0123456 7 Deflection mm Force N SW30 Injection molding SW30 MAH PP5 Injection molding SW30 Compression molding SW30 MAH PP5 Compression molding Figure 6 Impact resistance maximum force of hard wood fiber PP compos ites and soft wood fiber PP composites b with and without compatibilizer in both processes View this art in color at Wood Fiber Reinforced Polypropylene Composites881 ORDER REPRINTS a b 0 0 5 1 1 5 2 2 5 3 Damping index Injection moldingCompression molding HW30 PP70 HW30 PP70 MAH PP5 HW50 PP50 HW50 PP50 MAH PP5 0 0 5 1 1 5 2 2 5 3 Damping index Injection moldingCompression molding SW30 PP70 SW30 PP70 MAH PP5 SW50 PP50 SW50 PP50 MAH PP5 Figure 7 Damping index of hard wood fiber PP composites a and soft wood fiber PP composites b with and without compatibilizer in both processes View this art in color at 882Bledzki and Faruk ORDER REPRINTS a b Figure 8 SEM micrograph of hard a and soft b wood fiber PP composites in compression molding process wood fiber content 30 Wood Fiber Reinforced Polypropylene Composites883 ORDER REPRINTS a b Figure9 SEM micrographsof fracturedsurfaceof soft wood fi