Influence of nonmetals recycled from waste printed circuit boards

Influence of nonmetals recycled from waste printed circuit boards on flexural properties and fracture behavior of polypropylene compositesYanhong Zheng,Zhigang Shen *,Chujiang Cai,Shulin Ma,Yushan XingBeijing Key Laboratory for Powder Technology Research and Development,Beijing University of Aeronautics and Astronautics,Beijing 100191,People’s Republic of Chinaa r t i c l e i n f o Article history:Received 20May 2008Accepted 1July 2008Available online 10July 2008Keywords:Composites (A)Fracture (E)Scanning electron microscopy (G)a b s t r a c tFlexural strength and flexural modulus of the composites can be successfully improved by filling nonmet-als recycled from waste printed circuit boards (PCBs)into polypropylene (PP).By using scanning electron microscopy (SEM),the influence of nonmetals on fracture behavior of PP composites is investigated by in situ flexural test.Observation results show that the particles can effectively lead to mass micro cracks instead of the breaking crack.The process of the crack initiation,propagation and fiber breakage dissipate a great amount of energy.As a result,the flexural properties of the composites can be reinforced signif-icantly.Results of the in situ SEM observation and analysis to the dynamic flexural process supply effec-tive test evidence for the reinforcing mechanism of the nonmetals/PP composites on the basis of the energy dissipation theory.Ó2008Elsevier Ltd.All rights reserved.1.IntroductionNonmetals,an industrial solid-waste byproduct,are produced in large quantities during the recycling of waste printed circuit boards (PCBs)by physical method.Thousands of millions of tons of nonmetals are generated in the world each year.A huge source of pollution,nonmetals can also be a huge resource.The storage and disposal of nonmetals,designed to avoid environmental pollu-tion,have become a worldwide problem,and the reuse of nonmet-als is becoming increasingly important.Traditionally,the nonmetals are landfilled or incinerated,which will cause resource waste and potential environment problems.Recently,many researchers have used nonmetals as fillers for paints,adhesives,decorating agents and building materials,polyester composite and phenolic molding compound [1–6].But so far,according to author’s knowledge little work has been reported on the use of nonmetals as fillers for polypropylene (PP).PP as one of the most important commodity polymers is widely used in the packaging,textile and automobile industries because of its good processibility and great recyclability [7–10].Its application as an engineering thermoplastic is somewhat limited because of its poor fracture behavior.In fact if it is reinforced using filler or fiber it can be used instead of other commodity thermoplastic and even engineering thermoplastics [8–12].Nonmetals recycled fromwaste PCBs contain 50–70%glass fibers having high length diame-ter ratio,high elastic modulus and low elongation.Therefore,non-metals recycled from waste PCBs represent a potential substitute for traditional mineral fillers or pure glass fibers and can highly im-prove the strength of plastic products.They have more advantages than traditional fillers.Although the nonmetals recycled from waste PCBs can be successfully reused as reinforcing fillers in PP composites,influ-ence of them on fracture behavior of the composites cannot be neglected.Up to now,the research of particles reinforcing of polymer was mostly going on at the end of the experiment and was based on the results of the experiment,while the pro-cess of the particles reinforcing was unclear.Despite the impor-tance of fracture behavior of polymer materials,there are limited studies dealing with the fracture behavior in GF/PP,CaCO 3/PP,and GB/PPO composites [9,10,13–15].These research works have mostly been focused on the fracture behavior of composites via tensile test or notched flexural test.But according to author’s knowledge there is no evidence to show that investigation of fracture behavior of composites via unnotched flexural test has been performed.In this article,the objective of the research is to study the dy-namic process of nonmetals particles reinforcing of PP polymer.In nonmetals/PP composites,the dynamic process of the crack ini-tiation,propagation and fiber breakage are watched under scan-ning electron microscope (SEM)in situ unnotched flexural tests.These changes caused by nonmetals supply effective test evidence for the reinforcing mechanism of the nonmetals/PP composites on the basis of the energy dissipation theory.0261-3069/$-see front matter Ó2008Elsevier Ltd.All rights reserved.doi:10.1016/j.matdes.2008.07.004*Corresponding author.Tel./fax:+861082317516.E-mail address:shenzhg@ (Z.Shen).Materials and Design 30(2009)958–963Contents lists available at ScienceDirectMaterials and Designj o u r n a l h o m e p a g e :w w w.e l s e vier.c om/loc ate/matdes2.Experimental2.1.Material and fabrication procedure of compositesNonmetals,an industrial solid-waste byproduct,are produced in large quantities during physical recycling waste PCBs.The waste PCBs consist of a wovenfiberglass(modified,50–70%)mat impreg-nated with thermoset resins(epoxy resin or phenolic resin,etc., 30–50%).By vibrating screen classification,large quantities of non-metals with different particle size can be obtained.The nonmetals, with particle size of less than150meshes,were selected for mak-ing composites.Microscopic observation shows that most of them are single glassfibers and thermosetting resin powders(see Fig.1). They contain about70wt%single glassfibers.These glassfibers possess many excellent characteristics,such as high length diame-ter ratio(L/D ratio),high elastic modulus,low elongation and low thermal conductivity.To improve the dispersion of nonmetals particles in PP matrix and the compatibility between the nonmetals and matrix,all the nonmetals are modified with1.0wt%content of silane coupling agent KH-550(c-Aminopropyltriethoxysilane,Nanjing Shuguang Chemical Group Co.,Ltd.,China)through silanization for30min at80°C with high speed mixer(SHR-5A,Zhangjiagang Qiangda Plastics Machinery Co.,Ltd.,China)at1800rpm.Before the silan-ization,40vol%content of KH-550is mixed and hydrolyzed in the solvent(ethanol–water,volume ratio7:3)for30min at room temperature(23°C)and500rpm in a stirrer.PP powder S1003 [Beijing Yanshan Petrochemical Co.,Ltd.,China,meltflow rate 3.6g/10min(ASTM D1238,230°C,and2.16kg)]is used as the ma-trix polymer.The PP powders and the modified nonmetals particles are dried at80°C for2h.Then,the dried nonmetals particles and PP powers are stirred and mixed by using high speed mixer.The nonmetals/PP blends are extruded into thread with a screw extru-der(TE-35,Coperion Keya(Nanjing)Machinery Co.,Ltd.,China)at 210°C and220rpm.The extrudate is pelletized,dried for2h at 90°C.Then standardflexural specimens were made through injec-tion molding using an injection machine(CJ108M3V,Chen De Plas-tics Machinery Co.,Ltd.)at200°C.2.2.Flexural testFlexural test was carried out according to ISO178:1993stan-dards using an electronic universal testing machine(DXLL-10000, No.4Chemical Machinery Plant of Shanghai Chemical Equipment Co.,Ltd.,China)at a cross head speed of2mm/min.Five specimens for each type of composite were tested at room temperature (23°C),and the mean values were reported.2.3.Differential scanning calorimetry(DSC)measurementDSC measurements of PP composites with and without nonmet-als recycled from waste PCBs were carried out with DSC-SP equip-ment(Rheometric Scientific,Ltd.,USA)in aflowing nitrogen atmosphere.The temperature range utilized was from room tem-perature to300°C at a heating rate of10°C/min.Endothermic reactions as a function of the temperature were plotted as negative heatflow.2.4.In situ SEM experimental setup and observation inflexural testTo determine fracture behavior of pure PP and PP composites with nonmetals,a specially designed small load frame(see Fig.2)was built and utilized to apply three-pointflexural loading. The small load frame with a specimen is under a SEM(S-570,Hit-achi,Ltd.,Japan).Specimen dimension was6mm wide and2mm thick in gauge section.One side surfaces of specimens were pol-ished and coated with a thin layer of gold prior to microscopy to avoid charge build up.The dynamic fracture process of pure PP and PP composites was observed in the system of in situ SEM unnotchedflexural test when external load are imposed on the composites.3.Results and discussion3.1.Flexural propertiesFig.3shows theflexural properties of pure PP and nonmetals/ PP composites byfilling the nonmetals particles(0–30wt%)at room temperature.The content of the coupling agent was1wt%. The particle sizes of thefillers are less than150meshes.Theflex-ural strength of pure PP is35.53MPa,and theflexural strength of PP composite is greatly increased to46.81MPa byfilling10wt% nonmetals.Theflexural strength of PP composite increases quickly as the nonmetals contents increase and are56.08MPa with addi-tion of20wt%nonmetals.As the nonmetals contents increase to 30wt%,theflexural strength is further improved and reaches 66.25MPa in the experiment.The increases of theflexural moduli of composites are greater than that fromflexural strengths.The flexural modulus of pure PP is1.64GPa,and theflexural modulus of PP composite is greatly increased to2.49byfilling10wt%non-Fig.1.SEM micrograph of nonmetals recycled from wastePCBs.Fig.2.A load frame built for SEM observation.Y.Zheng et al./Materials and Design30(2009)958–963959metals.The flexural modulus of PP composite increases quickly as the nonmetals contents increase and are 3.13GPa with addition of 20wt%nonmetals.As the nonmetals contents increase to 30wt%,the flexural modulus of the composite is further improved and reach 3.82GPa.In other words,the flexural properties of the nonmetals/PP composites are increased with increasing the nonmetals contents from 10to 30wt%.The maximum increment of the flexural strength and flexural modulus is 86.5%and 133.0%,respectively.It is evident that the presence of nonmetals recycled from waste PCBs is an important factor in influence on flexural properties of the nonmetals/PP composites.3.2.DSC analysisDSC offers a convenient means of studying the reaction rates and mechanisms under controlled conditions.This value is partic-ularly important for conversion of the material into product for their potential practical application.Table 1summarizes the results of the DSC tests of pure PP and nonmetals/PP composites by filling the nonmetals particles (0–30wt%).The endothermic peak (T m )of pure PP is 168.4°C and the heat of fusion (D H m )is 77.5J/g.The T m of the nonmetals/PP composites are 165.1,165.5,166.8°C and the D H m of the compos-ites are 57.5,52.3,50.4J/g with the addition of 10,20,and 30wt%nonmetals,respectively.This indicates that addition of the filler into PP changes little in the T m of the composite,but that the D H m decreases by 27.1J/g with the addition of 30wt%nonmetals.Reduction of the T m is caused because of no nucleating effect of the nonmetals.And reduction of the D H m can be attributed to substi-tution of PP by nonmetals possessing low thermal conductivity.In a word,the addition of the nonmetals into PP leads to a decrease in the T m and D H m of the composites.Table 1also shows that the T m of pure PP and nonmetals/PP composite range from 165.1to 168.4°C,and this indicated that PP,both in the pure state and in the composite,exhibited onlythe crystal form a because the melting temperature of a crystals is 160–176°C [16].3.3.In situ SEM observation and analysisThe flexural properties results show that strength and rigidity of the composites are significantly improved by filling the non-metals into PP.With such millions of glass fibers and good com-patibility between the nonmetals and matrix,there are mass excellent supporting bodies,and appropriate interfacial adhesives are formed between the particles and matrix.Every dispersed particle triggers effective stress concentrations and lead to mass crazes so that the big cracks cannot be formed in the nonmet-als/PP composites.The process of the crack initiation,propagation and fiber breakage dissipate a great amount of energy.Thus,the matrix properties are improved with the addition of nonmetals particles into PP.In this study,the effect of particles on fracture behavior of PP composites is observed and analyzed during in situ SEM observation in three-point flexural test.All results are summarized as follows.Fig.4shows the SEM micrographs for the in situ observation of pure PP under the three-point flexural loading.The loading direc-tion is horizontal.The surface of the specimen of the pure PP is smooth without loading as shown in Fig.4a.At the beginning of the flexural loading,there is no change.When up to a certain load-ing it triggers many initial cracks,and the size of the crack is usu-ally big,nearly parallel to the load direction as shown in Fig.4b.Subsequently,more cracks appear following crazes thickening (Fig.4c),and extend to the dominant crack rapidly.Then the pure PP specimen gets flexural failure (Fig.4d).Fig.5shows the SEM micrographs for the in situ observation of the PP composite filled with nonmetals recycled from waste PCBs (30wt%)under the three-point flexural loading.The loading direc-tion is horizontal.For in situ SEM observation,the nonmetals/PP composite get polishing treatment,and many single fibers are ex-posed on the surface of the composite (Fig.5a).But the resin pow-ders particle size is smaller than glass fibers and they are intimately mixed in the PP matrix,which cannot be easily distin-guished in the composite.Furthermore,the particles are dispersed well in the matrix and the nonmetals are well wetted with PP material because of good compatibility between nonmetals and matrix (Fig.5b).And the glass fibers in the matrix are nearly per-pendicular to the load direction.That is mainly because the speci-men was made through injection molding using an injection machine.The glass fibers isotropy induced by fiber orientation is beneficial to flexural properties of the nonmetals/PP composites.Fig.5a shows the initial condition of the composite specimen with-out the flexural loading.At the beginning of the flexural loading,the SEM micrograph of the specimen shows no change,just as pure PP.When up to a certain loading,it triggers an initial micro crack,and craze is propagated by moving towards the interface of the particle and matrix.Then the crack is either terminated when it meets another particle or branched into mass finer crazing instead of the breaking crack directly (Fig.5b).Meanwhile,the partial interfacial debonding between the fiber ends and matrix can be seen at the bright place in Fig.5b and c.As the flexural loading in-creases,it breaks the single glass fiber (Fig.5c).When the loading further increases,mass broken fibers appear (Fig.5d).That is mainly because the glass fibers possess high elastic modulus and low elongation,they first undertake the loading when external load is imposed on the composite.Meanwhile,the strength of the loading is far greater than that of the single glass fiber,and there is strong adhesion and good compatibility between the fiber and the matrix,so the glass fibers are first broken compared with the PP matrix.Subsequently,the PP composite specimen gets flex-uralfailure.Fig.3.Flexural properties of the pure PP and nonmetals/PP composites.Table 1DSC data of the pure PP and nonmetals/PP composite PP content (wt%)Nonmetals content (wt%)T m (°C)D H m (J/g)1000168.4377.529010165.1457.518020165.5152.337030166.8250.36960Y.Zheng et al./Materials and Design 30(2009)958–963Results show that the pure PP matrix can initiate big cracks in the flexural test by in situ SEM observation.On increasing the load-ing,the bigger one of the cracks is extended into the dominant crack rapidly and then the pure PP specimen gets flexural failure rapidly.It means that the main energy absorption is in the crack initiation.While nonmetals recycled from waste PCBs are filled into PP matrix,mass micro cracks are triggered in the composite specimen.The crack is either terminated when it meets another particle or branched into mass finer crazing instead of the breaking crack directly.Since glass fiber acts like a barrier,craze cannot pass easily.In this condition,the crazes should turn glass fiber,move to-ward interface or break the glass fibers.The process of the crack initiation,propagation and fiber breakage dissipate a great amount of energy.Meanwhile,in the process of the flexural loading,partial interfacial debonding can slowdown the propagation of the crack and promote crack termination.These factors cause improvement of the flexural properties of the nonmetals/PP composites by filling the nonmetals particles recycled from waste PCBs evidently.The results of the in situ observation and analysis to the dynamic pro-cess supply effective test evidence for the reinforcing mechanismof the nonmetals/PP composites on the basis of the energy dissipa-tion theory.4.ConclusionsFlexural strength and flexural modulus of the composites can be successfully improved by filling nonmetals recycled from waste PCBs into PP.And the T m and D H m of the composites decrease with the addition of the nonmetals.The dynamic flexural process of the pure PP and nonmetals/PP composites are observed with SEM.Results show that the pure PP matrix can initiate big cracks under the flexural loading,and it extends to the dominant crack rapidly as the flexural loading in-creases.It means that the main energy absorption is in the crack initiation.While nonmetals are filled into PP matrix,mass micro cracks are triggered and consume tremendous energy.The glass fi-ber acts like a barrier,craze cannot pass easily.Therefore,the crazes should turn glass fiber,move toward interface or break the glass fibers.The process of the crack propagation and fiber breakage dissipate a great amount of energy.Meanwhile,intheFig.4.SEM micrograph for the in situ observation of the pure PP.(a)Initial condition;(b)triggering initial crack;(c)appearance of more cracks;and (d)flexural failure.The loading direction is horizontal.Y.Zheng et al./Materials and Design 30(2009)958–963961process of the flexural loading,partial interfacial debonding can slowdown the propagation of the crack and promote crack termi-nation.All of these factors can prevent and delay the nonmetals/PP composites getting flexural failure,and cause the improvement of the flexural properties evidently.In situ SEM observation and analysis experimental results show that energy dissipation is the major factor of reinforcing mecha-nism.In situ observation and analysis to the dynamic process sup-ply effective test evidence for the reinforcing mechanism of the nonmetals/PP composites on the basis of the energy dissipation theory.AcknowledgementsThe authors acknowledge with gratitude the financial support of the National Natural Science Foundation of China (Grant No.50774003),China Postdoctoral Science Foundation funded project (Grant No.20070420286)and the Joint Building Project of Beijing Education Committee.References[1]Yokoyama S,Iji M.Recycling of thermosetting plastics waste from electroniccomponent production processed.In:Proceedings of the IEEE international symposium on electronics and the environment.Orlando:IEEE;1995.[2]Iji M.Recycling of epoxy resin compounds for moulding electroniccomponents.J Mater Sci 1998;33:45–53.[3]Hong SG,Su SH.The use of recycled printed circuit boards as reinforcing fillersin the polyester composite.J Environ Sci Heal 1996;A31:1345–59.[4]Mou P,Xiang D,Pan X,Wa L,Gao J,Duan G.New solutions for reusingnonmetals reclaimed from waste printed circuit boards.In:Proceedings of the IEEE international symposium on electronics and the environment.New Orleans:IEEE;2005.[5]Li J,Lu H,Guo J,Xu Z,Zhou Y.Recycle technology for recovering resources andproducts from waste printed circuit boards.Environ Sci Technol 2007;41:1995–2000.[6]Guo J,Rao Q,Xu Z.Application of glass-nonmetals of waste printed circuitboards to produce phenolic moulding compound.J Hazard Mater 2008;153:728–34.[7]Liang JZ,Li RKY.Mechanical properties and morphology of glass bead-filledpolypropylene composites.Polym Compos 1998;19(6):698–703.[8]Liang JZ.Toughening and reinforcing in rigid inorganic particle filledpolypropylene:a review.J Appl Polym Sci 2002;83:1547–55.[9]Zebarjad SM,Bagheri R,Lazzeri A,Serajzadeh S.Fracture behaviour of isotacticpolypropylene under static loading condition.Mater Design2003;24:105–9.Fig.5.SEM micrograph for the in situ observation of the nonmetals/PP composite (30wt%).(a)Initial condition;(b)triggers an initial crack and interfacial debonding;(c)fibers breakage;and (d)mass fibers breakage.The loading direction is horizontal.962Y.Zheng et al./Materials and Design 30(2009)958–963[10]Zebarjad SM,Tahani M,Sajjadi SA.Influence offiller particles on deformationand fracture mechanism of isotactic polypropylene.J Mater Process Technol 2004;155–156:1459–64.[11]Lai CY,Sapuan SM,Ahmad M,Yahya N,Dahlan KZHM.Mechanical andelectrical properties of coconut coirfiber–reinforced polypropylene composites.Polym-Plast Technol Eng2005;44(4):619–32.[12]Arib RMN,Sapuan SM,Ahmad MMHM,Paridah MT,Khairul Zaman HMD.Mechanical properties of pineapple leaffibre reinforced polypropylene composites.Mater Design2006;27(5):391–6.[13]Zebarjad SM.The influence of glassfiber on fracture behavior of isotacticpolypropylene.Mater Design2003;24:531–5.[14]Zebarjad SM,Bagheri R,Seyed Reihani SM,Forunchi M.Investigation ofdeformation mechanism in polypropylene/glassfiber composite.J Appl Polym Sci2003;87:2171–6.[15]Tsui CP,Tang CY,Lee TC.Tensile properties and damage behaviors of glass-bead-filled modified polyphenylene oxide under large strain.Polym Compos 2001;22(6):742–51.[16]Shieh YH,Lee MS,Chen SA.Crystallization behavior,crystal transformation,and morphology of polypropylene/polybutene-1blends.Polymer2001;42: 4439–48.Y.Zheng et al./Materials and Design30(2009)958–963963。