Skip to content
BY 4.0 license Open Access Published by De Gruyter August 1, 2019

The Influence of Mechanical Recycling on Properties in Injection Molding of Fiber-Reinforced Polypropylene

  • T. Evens , G.-J. Bex , M. Yigit , J. De Keyzer , F. Desplentere and A. Van Bael


Due to higher mechanical demands on technical parts, the application of short fiber reinforced thermoplastics for injection molding is strongly increasing. Therefore, more attention needs to be paid to the optimization of their recycling processes. Mechanical shredding of thermoplastics into granules is a common recycling method within polymer industries. The breaking of polymer chains and reinforcing fibers during this process may affect the material properties. This study presents the effect of ten recycling sequences on four different materials: polypropylene, glass fiber filled polypropylene, carbon fiber filled polypropylene and flax fiber filled polypropylene. Tests indicate that recycling has a negative influence on most of the mechanical properties. Polypropylene without fibers forms an exception as it does not exhibit any significant change in material properties. Glass fiber and carbon fiber reinforced polypropylene show a decrease in stiffness and tensile strength during the recycling steps. The impact strength of carbon and flax fiber reinforced polypropylene increases whereas that of glass fiber reinforced polypropylene decreases.

*Correspondence address, Mail address: Tim Evens, KU Leuven, Diepenbeek Campus, Materials Technology TC, Wetenschapspark 27, 3590 Diepenbeek, Belgium, E-mail:


Abbas, K. B., KnutssonA. B. and Berglund, S. H., “New Thermoplastics from Old”, Chemtech., 8, 502508 (1978)Search in Google Scholar

Abbas, K. B., “Reprocessing of Termoplastics”, Polym. Eng. Sci., 20, 376382 (1980) 10.1002/pen.760200510Search in Google Scholar

Akovali, G., Bernardo, C., Leidner, J. and Utracki, L., “Chapter 1 Frontiers in the Science and Technology of Polymer Recycling”, Springer Science + Business Media, Dordrecht, p. 357 (1998) 10.1007/978-94-017-1626-0Search in Google Scholar

Aksesson, D., Fuchs, T., Stöss, M., Root, A., Stenvall, E. and Skrifvars, M., “Effect of Mechanical Recycling on Surface Appearance in Injection Molding of Polymers”, J. Appl. Polym. Sci., 133, 4387743885 (2015) 10.1016/2015.01.119.2015Search in Google Scholar

Bajracharya, R., Manalo, A., Karunasena, W. and Lau, K., “An Overview of Mechanical Properties and Durability of Glass-Fibre Reinforced Recycled Mixed Plastic Waste Composites”, Mater. Des., 62, 98112 (2014) 10.1016/j.matdes.2014.04.081Search in Google Scholar

Bernardo, C. A., Cunha, A. M. and Oliveira, M. J.: The Interfacial Interactions in Polymeric Composites”, G. Kluwer Academic Publishers, Dordrecht (1993)Search in Google Scholar

Bernasconi, A., Rossin, D. and Armanni, C., “Analysis of the Effect of Mechanical Recycling upon Tensile Strength of a Short Glass Fibre Reinforced Polyamide 6,6”, Eng. Fract. Mech., 74, 627641 (2007) 10.1016/j.engfracmech.2006.10.002Search in Google Scholar

Bourmaud, A., Baley, C., “Investigations on the Recycling of Hemp and Sisal Fibre Reinforced Polypropylene Composites”, Polym. Degrad. Stab., 92, 10341045 (2007) 10.1016/j.polymdegradstab.2007.02.018Search in Google Scholar

Bowyer, W. H., Bader, M. G., “On the Re-Inforcement of Thermoplastics by Imperfectly Aligned Discontinuous Fibres”, J. Mater. Sci., 11, 13151321 (1972) 10.1007/bf00550698Search in Google Scholar

Cantwell, W. J., Morton, J., “The Impact Resistance of Composite Materials – A Review”, Composites, 22, 347362 (1991) 10.1016/0010-4361(91)90549-VSearch in Google Scholar

Colucci, G., Simon, H., Roncato, D., Martorana, B. and Badini, C., “Effect of Recycling on Polypropylene Composites Reinforced with Glass Fibres”, J. Thermoplast. Compos. Mater., 30, 707723 (2017) 10.1177/0892705715610407Search in Google Scholar

Doumbai, A., Castro, M., Jouannet, D., Kervoëlen, A., Falher, T., Cauret, L. and Bourmaud, A., “Flax/Polypropylene Composites for Lightened Structures: Multiscale Analysis of Process and Fibre Parameters”, Mater. Des., 87, 331341 (2015) 10.1016/j.matdes.2015.07.139Search in Google Scholar

Driscoll, S. B., “Thermoplastic Resin Regrind Study”, SPE ANTEC Tech. Papers, 536–538 (1977)Search in Google Scholar

Filbert, W. C., “Glass Reinforced 6 6 Nylon – The Effect of Moulding Variables on Fibre Length and the Relation of Fibre Length to Physical Properties”, SPE ANTEC Tech. Papers, 836–841 (1968)Search in Google Scholar

Giraldi, A., Bartoli, J., Velasco, J. and Mei, L., “Glass Fibre Recycled Poly(ethylene terephthalate) Composites: Mechanical and Thermal Properties”, Polym. Test., 24, 507512 (2005) 10.1016/j.polymertesting.2004.11.011Search in Google Scholar

Gourier, C., Bourmaud, A., Le Duigou, A. and Baley, C., “Influence of PA11 and PP Thermoplastic Polymers on Recycling Stability of Unidirectional Flax Fibre Reinforced Biocomposites”, Polym. Degrad. Stab., 136, 19 (2017) 10.1016/j.polymdegradstab.2016.12.003Search in Google Scholar

Gutiérrez, E., Bono, F., “Chapter 4 Review of Industrial Manufacturing Capacity for Fibre-Reinforced Polymers as Prospective Structural Components in Shipping Containers”, in JRC Scientific and Policy Reports, Publications Office of the European Union, Luxembourg, p. 1214 (2013)Search in Google Scholar

Huber, T., Müssig, J., “Fibre Matrix Adhesion of Natural Fibres Cotton, Flax and Hemp in Polymeric Matrices Analyzed with the Single Fibre Fragmentation Test”, Compos. Inferfaces, 15, 335349 (2008) 10.1163/156855408783810948Search in Google Scholar

Ignatyev, I., Thielemans, W. and Vander Beke, B., “Recycling of olymers: A Review”, Chemisty & Sustainability Energy & Materials, 7, 15791593 (2014) 10.1002/cssc.201300898Search in Google Scholar

Jacob, A., “Composites Can Be Recycled”, J. Reinf. Plast. Compos., 55, 645 (2011). 10.1016/S0034-3617(11)70079-0Search in Google Scholar

Kelly, A., Tyson, W. R., “Tensile Properties of Fibre-Reinforced Metals: Copper/Tungsten and Copper/Molybdenum”, J. Mech. Phys. Solids, 13, 329338 (1965) 10.1016/0022-5096(65)90035-9Search in Google Scholar

Ku, H., Wang, H., Pattarachaiyakoop, N. and Trada, M., “A Review on the Tensile Properties of Natural Fiber Reinforced Polymer Composites”, Composites, 42, 856873 (2011) 10.1016/j.compositesb.2011.01.010Search in Google Scholar

Kuram, E., Ozcelik, B. and Yilmaz, F., “The Influence of Recycling Number on the Mechanical, Chemical, Thermal and Rheological Properties of Poly(butylene terephthalate)/Polycarbonate Binary Blend and Glass-Fibre Reinforced Composite”, J. Thermoplast. Compos. Mater., 29, 14431457 (2016) 10.1177/0892705715569823Search in Google Scholar

Kuram, E., Ozcelik, B., Yilmaz, F., Timur, G. and Sahin, Z., “The Effect of Recycling Number on the Mechanical, Chemical, Thermal, and Rheological Properties of PBT/PC/ABS Ternary Blends: With and without Glass-Fiber”, Polym. Compos., 35, 20742084 (2014) 10.1002/pc.22869Search in Google Scholar

La Mantia, F. P., “Effect of Fillers on the Properties of Recycled Polymers”, Macromol. Symp., 194, 101110 (2003) 10.1002/masy.200390070Search in Google Scholar

Le Duigou, A., Pillin, I., Bourmaud, A., Davies, P. and BaleyC., “Effect of Recycling on Mechanical Behaviour of Biocompostable Flax/Poly(L-lactide) Composites”, Composites, 39, 14711478 (2008) 10.1016/j.compositesa.2008.05.008Search in Google Scholar

Leidner, J.: Plastics Waste, Recovery of Economic Value, Marcel Dekker, New York (1981)Search in Google Scholar

Leidner, J., “Effect of Recycling on Mechanical Behaviour of Biocompostable Flax/Poly(L-lactide) Cmposites”, Composites, 39, 14711478 (2008) 10.1016/j.compositesa.2008.05.008Search in Google Scholar

Mehat, N., Kamaruddin, S., “Optimization of Mechanical Properties of Recycled Plastic Products via Optimal Processing Parameters Using the Taguchi Method”, J. Mater. Process. Technol., 211, 19891994 (2011) 10.1016/j.jmatprotec.2011.06.014Search in Google Scholar

Oliveux, G., Dandy, O. and Leeke, G., “Current Status of Recycling of Fibre Reinforced Polymers: Review of Technologies, Reuse and Resulting Properties”, Prog. Mater. Sci., 72, 6199 (2015) 10.1016/j.pmatsci.2015.01.004Search in Google Scholar

Pickering, K. L., Aruan Efendy, M. G. and Le, T. M., “A Review of Recent Developments in Natural Fibre Composites and their Mechanical Performance”, Composites, 83, 98112 (2016) 10.1016/j.compositesa.2015.08.038Search in Google Scholar

Sánchez, P., Remiro, P. M. and Nazábal, J., “Influence of Reprocessing on the Mechanical Properties of a Commercial Polysulfone/Polycarbonate Blend”, Polym. Eng. Sci., 32, 861867 (1992) 10.1002/pen.760321305Search in Google Scholar

Shea, J., NelsonE. D., “Effect of Recycling on the Properties of Injection Molded Polycarbonate”, SPE ANTEC Tech. Papers, 614617 (1975)Search in Google Scholar

Thomason, J. L., “The Influence of fibre Length and Concentration on the Properties of Glass Fibre Reinforced Polypropylene: 5. Injection Moulded Long and Short Fibre PP”, Composites, 33, 16411652 (2002) 10.1016/S1359-835X(02)00179-3Search in Google Scholar

Throne, J. L., “Effect of Recycle on Properties and Profits: Algorithms”, Adv. Polym. Technol., 7, 347360 (1987) 10.1002/adv.1987.060070401Search in Google Scholar

Witten, E., Sauer, M. and Kühnel, M.: “Chapter 3 Composites Market Report 2017”, Intustrievereinigung Verstärkte Kunststoffe, Munich, p. 67 (2017)Search in Google Scholar

Yan, X., Cao, S., “Structure and Interfacial Shear Strength of Polypropylene-Glass Fiber/Carbon Fiber Hybrid Composites Fabricated by Direct Fiber Feeding Injection Molding”, Compos. Struct., 185, 362372 (2018) 10.1016/j.compstruct.2017.11.037Search in Google Scholar

Yang, H. W., Farris, R. and Chien, J. C., “Study of the Effect of Regrinding on the Cumulative Damage to the Mechanical Properties of Fiber-Reinforced Nylon 66”, J. Appl. Polym. Sci., 23, 33753382 (1979) 10.1002/app.1979.070231121Search in Google Scholar

Zhu, J., Zhu, H., Njuguna, J. and Abhyankar, H., “Recent Development of Flax Fibres and their Reinforced Composites Based on Different Polymeric Matrices”, Materials, 6, 51715198 (2013) PMid:28788383; 10.3390/ma6115171Search in Google Scholar PubMed PubMed Central

Received: 2018-10-04
Accepted: 2019-02-15
Published Online: 2019-08-01
Published in Print: 2019-08-13

© 2019, Carl Hanser Verlag, Munich

This work is licensed under the Creative Commons Attribution 4.0 International License.

Downloaded on 9.2.2023 from
Scroll Up Arrow