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Journal of Environmental Management 91 (2010) 2505e2510

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Journal of Environmental Management

journal homepage: www.elsevier .com/locate/ jenvman

PVC-based composite material containing recycled non-metallic printed circuitboard (PCB) powders

Xinjie Wang a,b, Yuwen Guo a,*, Jingyang Liu a, Qi Qiao a, Jijun Liang a

aChina Environmental Science Research Institute, Beijing, Postal Code 100012, PR Chinab Yili Teachers College, Kuitun, Xinjiang, Postal Code 833200, PR China

a r t i c l e i n f o

Article history:Received 14 December 2009Received in revised form2 June 2010Accepted 6 July 2010Available online 21 August 2010

Keywords:Printed circuit boardPaper-basedPolyvinylchlorideComposite materials

* Corresponding author. Tel.: 010 84915256; fax: 01E-mail address: guoyw@craes.org.cn (Y. Guo).

0301-4797/$ e see front matter � 2010 Elsevier Ltd.doi:10.1016/j.jenvman.2010.07.014

a b s t r a c t

The study is directed to the use of non-metallic powders obtained from comminuted recycled paper-based printed circuit boards (PCBs) as an additive to polyvinyl chloride (PVC) substrate. The physicalproperties of the non-metallic PCB (NMPCB) powders were measured, and the morphological,mechanical and thermal properties of the NMPCB/PVC composite material were investigated. The resultsshow that recycled NMPCB powders, when added below a threshold, tended to increase the tensilestrength and bending strength of PVC. When 20 wt% NMPCB powders (relative to the substrate PVC) ofan average diameter of 0.08 mm were added, the composite tensile strength and bending strengthreached 22.6 MPa and 39.83 MPa, respectively, representing 107.2% and 123.1% improvement over purePVC. The elongation at break of the composite material reached 151.94% of that of pure PVC, while theVicat softening temperature of the composite material did not increase significantly compared to thepure PVC. The above results suggest that paper-based NMPCB powders, when used at appropriateamounts, can be effective for toughening PVC. Thus, this study suggests a new route for reusing paper-based NMPCB, which may have a significant beneficial environmental impact.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

Printed circuit boards (PCB) are widely used in electric andelectronic products. PCB can be classified according to the materialused in the PCB substrate, e.g., paper-based (FR-1, FR-2, XPC),composite material based, or fiberglass based (FR-4) PCB, and so on.In mainland China, the production of paper-based PCB was about27 000 tons in year 1996, about 63 000 tons in 2000, and about1 00 000 tons in 2005, making China the No. 1 country in the worldin paper-based PCB production and consumption (Gu, 2002). Chinahas recently entered a time for retiring a large number of electricappliances (Wang and Shang, 2006). An enormous amount of wastepaper-based PCB are being disposed improperly, e.g., illegallyincinerated, which led to large amount of organic pollutants beingreleased into the air and underground water, causing substantialenvironmental harm (Yu et al., 2006). Thus, the recycling of thesePCBs has become a pressing environmental issue in China.

The efforts in recycling PCB have previously been focusing onthe recovery of metals in the PCB, while the non-metallic materialswere usually sent to landfills or subjected to incineration. To date,the research in the recycling of NMPCB centers on the materials

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used in computers, such as FR-4 non-metallic materials, which areusually fiberglass based. Chemical solvents are usually used forrecovering the resin and fiberglass in the NMPCB (Dang et al., 2005;Yu et al., 2005; Kubouchi et al., 2002); however, they generatea large amount of wastewater that needs further treatment, whichusually leads to secondary pollution.

Iji et al. reported the extraction offiberglass in the recycledwasteNMPCB for use as an additive for epoxy resins (Iji, 1998; Yokoyamaand Iji, 1995); Guo et al. used these fiberglass as filler for phenolicresin (Guo et al., 2008b); Zheng et al. used NMPCB powders asa reinforcing material in polypropylene (Zheng et al., 2009a,b); Banet al. used NMPCB powders to replace the standard non-metallicpowder sand (Ban et al., 2005). These reported applications ofNMPCB are largely based on the large amount of glass fibers in theFR-4 type PCB substrate. However, the vast majority of PCBs used inTVs, washing machines and other household electrical appliances,such as FR-1, FR-2, XPC, etc. (Li et al., 2005), are paper based. It wasreported that paper-basedNMPCBwas used as a substitute forwoodpowders as fillers for phenolic resins (Guo et al., 2008a). It is notedthat, in this cited study, the bending strength and flowability of thecomposite material worsened.

To the knowledge of the authors of this paper, there have notbeen reports on the preparation of composite materials based onPVC and paper-based NMPCB powders. PVC is a widely used

mailto:guoyw@craes.org.cnwww.sciencedirect.com/science/journal/03014797http://www.elsevier.com/locate/jenvmanhttp://dx.doi.org/10.1016/j.jenvman.2010.07.014http://dx.doi.org/10.1016/j.jenvman.2010.07.014http://dx.doi.org/10.1016/j.jenvman.2010.07.014

X. Wang et al. / Journal of Environmental Management 91 (2010) 2505e25102506

material due to its low combustibility and good corrosion resis-tance. However, it is low in toughness and elongation, and has poorthermal stability. It has been shown that adding rigid fillers parti-cles to PVC can improve its mechanical properties (Lu et al., 1999; Li,1995). Thus, it appears that the thermoset resins present in paper-based NMPCB powders can make the NMPCB powders suitable asfillers for making PVC composites. Accordingly, the instant study ofthe paper-based NMPCB/PVC composite material can have impor-tant applications in promoting resource re-utilization.

Fig. 1. An SEM image of paper-based NMPCBs.

2. Materials and experimental methods

2.1. Preparation of NMPCB materials

The paper-based PCBs (previously processed to remove metals)were mechanically crushed. The NMPCB powders thus obtainedwere separated and collected by electrostatic beneficiation. Ultra-fine grinder (RT-25, Taiwan) was used to further comminute theNMPCB powders, which were then screened by No. 180 and No. 60sieves, to obtain NMPCB powders of an average diameter of 0.08and 0.25 mm, respectively. No surface treatment or chemicalmodification was further performed on the NMPCB powders.

2.2. Preparation ofNMPCBpowders/PVC compositematerial samples

PVC was provided by Shenma Chloro-Alkali Development LLC,Henan Province, China, and formulated according to Table 1 below.The paper-based NMPCB powders obtained above were added tothe PVC substrate at levels of 10%, 20%, 30% based on the weight ofthe PVC in the formulation. (Adding larger amounts of NMPCBpowders (>30%) to PVC worsened the processibility of thecomposite material, and created great difficulty for injectionmolding.) The composite material was extruded in a twin-screwextruder (ZSK-25WLE, WP, Germany, the temperatures for theprocessing sections are 165 �C, 165 �C, 165 �C, 170 �C, 170 �C, 195 �C,195 �C,195 �C; twin-screw rotation speed: 180 r/min). The extrudedcomposite material was granulated, and then molded into testingsamples in a twin-screw injector (JPH10, Hong Lee Machine Co.,Ltd., Guangdong, China; the temperatures for the processingsections are 200 �C, 210 �C, 200 �C, and 180 �C).

2.3. Testing

Scanning ElectronMicroscopy (SEM) (JSM-6301F, UK)was used toobtain the morphology of the NMPCB particles as well as to performenergy spectrum analysis (elemental analysis) for the NMPCB parti-cles; S-520 SEM (Hitachi, Japan) was used to observe the fracturesurface of the NMPCB/PVC composite material. Surfaces of thesamples are coated with Au for improved electrical conductivity.

The tensile and bending properties of the NMPCB/PVC compositematerial samples were tested on the Universal Material TestingSystem (LR30K, LOIYD, UK) at 50 mm/min and 10 mm/min inaccordance with ISO 527-2:1993 and ISO 178:1993 standards. Vicatsoftening point was measured according to ISO 306:1994 at

Table 1PVC formulation.

Constituents Parts (by weight)

PVC 100Dibasic lead sulfate (thermal stabilizer) 2Tribasic lead sulfate (thermal stabilizer) 2Dibutyl phthalate (DBP, plasticizer) 10Stearic acid (lubricant) 0.2Wax 5

a heating rate of 50 �C/h and a load of 10 N, on XRW-300 (JinjianTesting Equipments, Chengde, Hebei province, China).

3. Discussion

3.1. Morphology of the NMPCB particles and energy spectrumanalyses

Fig. 1 shows a SEM image of paper-based NMPCB powders. Mostof the powders are present in irregularly shaped granules. A smallamount of glass fibers and fiber bundles are also observed. Paperfibers are not visible in the SEM image. As paper fibers are low intoughness and strength, in the comminution process for makingthe paper-based NMPCB powders, they were crushed anddispersed within the thermoset resin granules. As a comparison,Fig. 2 shows a SEM image of fiberglass-based NMPCB powders,where the glass fibers are largely separated from the thermosetresin. As fiberglass-based NMPCB/PVC composites can have highviscosity and are difficult to process using the equipments available

Fig. 2. An SEM image fiberglass-based NMPCBs.

Fig. 3. Energy spectrum analysis of selected regions a, b, and c in Fig. 1.

Fig. 4. An SEM image of the residues obtained by removing organic contents ofpaper-based NMPCBs.

Fig. 5. Energy spectrum analysis of residues obtained by removing organic contents ofpaper-based NMPCBs.

X. Wang et al. / Journal of Environmental Management 91 (2010) 2505e2510 2507

to the current authors, the comparative data regarding mechanicalproperties for fiberglass-based PCB/PVC composites are beyond thescope of this paper.

Energy spectrum analyses of selected points a, b, and c in Fig. 1are shown in Fig. 3. The fibers (point a) are determined to bemainlycomprised of silicon, while the irregularly shaped particles (pointsb and c) are mainly comprised of carbon. This indicates that thefibers are glass fibers, and the irregularly shaped particles arethermoset resin/paper composite.

To further characterize the composition of the NMPCB powders,theNMPCBpowderswereheated to900 �C inamuffle furnace toburn

Fig. 6. Tensile strength (6a) and elongation at break (6b) of paper-based NMPCB/PVCcomposite materials.

Fig. 8. Vicat softening temperature of paper-based NMPCB/PVC composite materials.

X. Wang et al. / Journal of Environmental Management 91 (2010) 2505e25102508

off organic compounds (including the thermoset resins and paperfibers), until the residue had reached a constantweight. Theweightofthe residuewasabout 20wt%of thatof the originalNMPCBbefore theheat treatment. The morphology of the residue is shown in Fig. 4.

Energy spectrum analyses were conducted to determine thecomposition of the residue. As shown in Fig. 5aed (Spectra 1e4,corresponding to the 4 selected regions in Fig. 4, respectively), thefibrous residue particles in the residue comprise mainly SiO2, CaO,Al2O3, and thusweredetermined tobe glassfiber. Irregularly shaped

Fig. 7. Bending properties of paper-based NMPCB/PVC composite materials.

particlesmainlycomprise SiO2, CaO, Al2O3, andMgO. These particlesmay be ceramics or metal oxides from the electronic devices thatwere not completely removed in the metal extraction process.

From the above analysis, we determine that the paper-basedNMPCB powders comprise primarily thermoset resin/paper fibercomposite, inorganic particles, and a small amount of glass fibers.The thermoset resinmakes up to about 80wt% of the NMPCB. In thefollowing, we present the results of using the paper-based NMPCBpowders as strength and toughness enhancer for PVC.

3.2. Mechanical properties of paper-based NMPCB/PVC compositematerials

3.2.1. Tensile propertiesFig. 6a shows the tensile strength for paper-based NMPCB/PVC

composite material containing different amounts of NMPCB.Compared with pure PVC, the tensile strength of the composite issignificantly greater due to the addition of NMPCB powders. Withthe increase of the amounts of NMPCB used, however, the tensilestrength first increases and then decreases. When the levels ofNMPCB are between 10% and 30%, the composite has about twofoldof the tensile strength of that of the pure PVC. The compositecontaining NMPCB particles of greater size (i.e., the 0.25 mm sizedparticles, the top curve) exhibit greater tensile strength at the sameweight amounts of NMPCB. This may be due to the fact thatsmaller-sized NMPCB particles more significantly increase theviscosity of the composite and also have greater propensity ofaggregation, which hinders their dispersion in the PVC substrateand negatively impacts the continuity of the PVC substrate matrix.

As can be seen from Fig. 6b, which shows the elongation at breakfor the NMPCB/PVC composite materials, NMPCB significantlyincrease the elongation at break of PVC, indicating that these fillersimprove not only the tensile strength but also the toughness of PVC.The smaller sized NMPCB powders appear to be more effective fortoughening the PVC than large-sized powders. This is because thesmall size particles have larger contact surface areas with the PVCmatrix. When external forces are applied, these smaller particlescan produce a large number of crazes for dissipating and/orabsorbing energy before rupture.

3.2.2. Bending propertiesAs shown in Fig. 7, at smaller NMPCB particle size (0.08 mm),

paper-based NMPCB/PVC composite material exhibit superiorbending properties compared to pure PVC. For example, whenNMPCB powders were added at 20 wt%, bending strength of thecomposite material reached 39.83 MPa, an increase of 123.1% overpure PVC. Further increasing the amounts of NMPCB cause the

Fig. 9. SEM images of fracture surface of paper-based NMPCB/PVC materials. The average diameter of the NMPCB particle is 0.08 mm (9a) and 0.25 mm (9b). A pure PVC fracturesurface is shown in (9c) for comparison.

X. Wang et al. / Journal of Environmental Management 91 (2010) 2505e2510 2509

bending strength of the material to worsen. In contrast, addingNMPCB of larger particle size (0.25 mm) tend to slightly worsen thebending property of the composite material.

Bending property is a mechanical property measured by theresponse of a material when it is subject to forces applied perpen-dicularly to its longitudinal axis, which leads to both tensile stressand compression stress (on different sides of longitudinal axis of thematerial) (Yu and Yan, 2007). The larger NMPCB particle size resul-ted in weaker adhesion between the particles and the PVC matrix,which acted as centers of stress concentration in the bending test.

3.3. Non-metallic/PVC composite Vicat softening temperature

Fig. 8 shows the Vicat softening temperature (VST) of paper-based NMPCB/PVC composite material. The addition of 0.25 mmNMPCB produced a downward trend in the VST, while addition of0.08 mm NMPCB slightly increased the VST of PVC.

Vicat softening temperature of the composite material is alsorelated to the interface adhesion between the NMPCB particles andthe PVC matrix. The strength of the interface adhesion affects thethermal movement of polymer chains of the PVC matrix, which inturn affects the viscosity and heat-resistance of the compositematerial. Smaller sized NMPCB particles form stronger interfaceinteractions with the PVC matrix and are more effective inrestricting the recoiling of the polymer chains at higher tempera-ture. However, at the same time, the tendency to aggregate thesmaller sized NMPCB particles somewhat weakens this effect.Overall, VST of the composite material containing the smaller sizedNMPCB is only improved slightly as compared to pure PVC.

3.4. Morphology of the fracture surface

Fig. 9a and b depict the SEM photos of the fracture surface of PVCcompositematerial samples loadedwith20wt%paper-basedNMPCBhaving particle size of 0.08 and 0.25 mm, respectively, after being

subjected to tensile strength tests discussed above. The smaller sizedNMPCB particles appear to be distributed uniformly across the frac-ture surface (Fig. 9a), although a slight aggregation is observed. Incontrast, the fracture surface for the material loaded with NMPCBhaving a larger particle size containsmore rupture holes. In addition,larger particles (shown in the circled area in Fig. 9b) tend to createstress concentrationpoints and interrupt the stress transmission overthe PVC matrix. As a comparison, the fracture surface of pure PVC(shown in Fig. 9c) is relatively smooth, indicating a brittle type frac-ture. The NMPCB/PVC composite materials in Fig. 9a and b displayrather rough fracture surface, suggesting that plastic deformationoccurred during rupture. This explains the improved toughness forthe NMPCB/PVC composite material.

4. Conclusion

We have studied the feasibility of using recycled paper-basednon-metallic PCB as additives for PVC. Our results indicate thatmechanically crushed NMPCB particles, without surface treatmentor modification, can be effectively employed to improve the tensilestrength and bending strength of PVC. This finding suggests a fairlystraightforward yet cost-effective way to reuse the waste non-metallic PCBs. In particular, we find that smaller sized NMPCBparticles are more effective in enhancing the toughness of PVC. Theoptimum loading level of NMPCB particles having average size of0.08 mm is about 20 wt% of that of the PVC substrate. The additionof NMPCB particles with small size slightly increases the thermalstability of PVC as reflected by the increased Vicat softeningtemperature. Larger sized NMPCB particles tend to worsen thethermal stability of the composite material.

Acknowledgements

This research is supported by Chinese National Public InterestEnvironmental Protection Research Fund No. HBGY200709006 and

X. Wang et al. / Journal of Environmental Management 91 (2010) 2505e25102510

China Environmental Research Institute Research Fund No.2007KYYW02.Theauthors also thankProfessorChengzhongWangatthe College of Material Science and Engineering, Beijing University ofChemical Technology for his assistance in the mechanical propertytesting of certain samples.

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PVC-based composite material containing recycled non-metallic printed circuit board (PCB) powdersIntroductionMaterials and experimental methodsPreparation of NMPCB materialsPreparation of NMPCB powders/PVC composite material samplesTesting

DiscussionMorphology of the NMPCB particles and energy spectrum analysesMechanical properties of paper-based NMPCB/PVC composite materialsTensile propertiesBending properties

Non-metallic/PVC composite Vicat softening temperatureMorphology of the fracture surface

ConclusionAcknowledgementsReferences