Comparative Study of the Cure Characteristics and Mechanical Properties of Natural Rubber Filled With Different Calcium Carbonate Resources Soma A. El Mogy , N. A. Darwish, A. Awad Polymer Metrology & Technology Department, National Institute of Standards (NIS), Giza, Egypt Bio-waste materials such as eggshell (ES) and fishbone (FB) were used as new fillers compared with commercial calcium carbonate (CC) in natural rubber composite. The effect of their presence in the rubber mix on the rheometric study, morphology, mechanical properties, hardness, and abrasion resistance has been investigated at constant filler content (30 phr). The filler and their composites were characterized by Fourier-transform infrared, X-ray diffraction, thermogravimetric analysis, and scanning electron microscope (SEM). The results showed that the cure time and scorch time of the com- posites filled with CC and ES are lower than the compos- ites filled FB filler. On the other hand, composites with ES and CC showed enhanced values of tensile, modulus at 100% and 300% elongation, hardness, and abrasion resistance. The morphological data revealed that CC and ES fillers are better dispersed in the rubber matrix than FB filler. J. VINYL ADDIT. TECHNOL., 2019. © 2019 Soci- ety of Plastics Engineers INTRODUCTION Natural rubber (NR) is one of the most important rub- bers with excellent properties. It is widely used in various industrial applications and products, either alone or in blend with other material such as seals and gaskets in auto- motive, hoses, tires, and pharmaceutical and food indus- tries. It is obtained from the latex of the Hevea brasiliensis (i.e., the Brazilian rubber tree) and has good physical prop- erties, such as low build-up, resistance to tear and impact, and high mechanical strength [1]. On the other hand, NR has a sensitivity to chemicals and solvents and low flame resistance causing limitation in different applications. The filler is one of the significant added substances uti- lized in the characteristic elastic compound and has impact and effect on elastic materials. Fillers play an important role in altering the physical properties of the base polymer. Also, fillers are added to polymer either to add attractive characteristics to the final compound and improve the prod- uct quality or to reduce the cost. Normally, carbon black and silica are usually used to improve the mechanical properties of rubber rather than the use them for rubber protection from chemical, solvent, and flame. However, due to their limited reserve and increasing need for devel- oping rubber composites based on cost-effective, biode- gradable and environmentally friendly materials, alternative rubber composites depending on biofillers are the most reg- arded research initiative [2–5]. In recent years, several researches have been dealt with biofillers for polymeric composites. These biofillers, which are extracted from either animal (e.g., sea shell, shrimp shell, eggshell [ES], fish wastes) or plants (e.g., jute, oil palm, flax, rice husk) can be used to replace the conven- tional; reinforcing fillers [6–9]. The food industry produces large amounts of solid wastes, which can end up in lakes, rivers, and water drains. The disposal of these wastes can lead to a very important problem, which can cause risk to public health, contamination of water resources and pollut- ing the environment. Among different solid waste materials available, ES and fishbone (FB) appeared to be useful fillers because their usage as reinforcing materials in poly- mers prevents contamination of water source or pollution of the environment. Also, ES is not only used in polymer but also used in cement and a ceramic wall tile paste [10–13]. The two natural fillers contain mainly calcium carbonate (CC) of about 95–97% in ES and of 78% in FB, and the rest are organic materials such as sulfated polysac- charides, type x-collagens, and other proteins [14–16]. CC is one of the important inorganic materials and has been widely used as mineral filler in plastics, rubber, and paints industry to reduce cost and to enhance physical, mechani- cal, and thermal properties [17]. In general, the CC and other mineral fillers are required in large amount to be added into the polymer. Hence, the cost becomes quite expensive. To overcome the factor of cost, the recent researches were focused on the use of natural wastes, which is nonhazardous, present in the environment, caus- ing a pollution problem. ES and FB are an important source of CC. Generally, the properties of NR composites are strongly dependent on the characteristics of the fillers and the ability of filler to be well dispersed in the rubber matrix. The CC is a type of filler that can be easily dispersed in polar Correspondence to: Soma A. El Mogy; e-mail: soma.elmogy@yahoo.com DOI 10.1002/vnl.21745 Published online in Wiley Online Library (wileyonlinelibrary.com). © 2019 Society of Plastics Engineers Journal of Vinyl and Additive Technology—2019