Synergistic Effect of Maleated Natural Rubber and Modified Palm Stearin as Dual Compatibilizers in Composites based on Natural Rubber and Halloysite Nanotubes

The performance of rubber composite relies on the compatibility between rubber and filler. This is specifically of concern when preparing composites with very different polarities of the rubber matrix and the filler. However, a suitable compatibilizer can mediate the interactions. In this study, composites of natural rubber (NR) with halloysite nanotubes (HNT) were prepared with maleated natural rubber (MNR) and modified palm stearin (MPS) as dual compatibilizers. The MPS dose ranged within 0.5–1.5 phr, while the MNR dose was fixed at 10 phr in all formulations. It was found that the mixed MNR/MPS significantly enhanced modulus, tensile strength, and tear strength of the composites. The improvements were mainly due to improved rubber-HNT interactions arising from hydrogen bonds formed in the presence of these two compatibilizers. This was clearly verified by observing the Payne effect. Apart from that, the MPS also acted as a plasticizer to provide improved dispersion of HNT. It was clearly demonstrated that MNR and MPS as dual compatibilizers improved rubber-HNT interactions and reduced filler-filler interactions, which then improved tensile and tear strengths, as well as dynamical properties. Therefore, the mix of MNR and MPS had a great potential to compatibilize non-polar rubber with HNT filler.

Maleated Natural Rubber/Halloysite Nanotubes Composites

In this study, maleic anhydride (MA) grafted natural rubber (NR), known as maleated natural rubber (MNR), was melt-prepared with the MA content varied within 1–8 phr. MNR was used as the main matrix, with Halloysite Nanotubes (HNT) as a filler, in order to obtain composites with improved performance. The compounds were investigated for their filler–filler interactions by considering their Payne effect. On increasing the MA content, scorch and cure times increased along with maximum torque and torque difference. The MNR with 4 phr of MA exhibited the least filler–filler interactions, as indicated by the retention of the storage modulus after applying a large strain to the filled compound. This MNR compound also provided the highest tensile strength among the cases tested. It is interesting to highlight that MNR, with an appropriate MA content, reduces filler–filler interactions, and, thereby, enhances the HNT filler dispersion, as verified by SEM images, leading to improved mechanical and dynamical properties.

Kesetimbangan Cair-Cair Sistem Polipropilena dan Maleated Natural Rubber

Pada campuran polipropilena (PP)-maleated natural rubber (MNR), MNR berfungsi sebagai compatibilizer yang melakukan modifikasi terhadap permukaan matrik PP untuk memudahkan masuknya filler sehingga dihasilkan campuran yang lebih kompatibel. Tujuan dari penelitian ini adalah untuk menentukan kemampuan campur maleated natural rubber (MNR) dalam polipropilena (PP) pada berbagai variasi suhu. Penelitian diawali dengan prediksi kesetimbangan cair-cair sistem PP-MNR dengan menggunakan metode UNIFAC dilanjutkan dengan validasi model kesetimbangan. Validasi model kesetimbangan cair-cair sistem PP-MNR diawali dengan mencampurkan karet alam dan maleic anhydride (MAH) dalam internal mixer untuk penyiapan MNR. MNR yang telah disiapkan lalu dicampurkan dengan PP dalam internal mixer dengan kadar MNR dan temperatur proses divariasi berdasarkan prediksi kesetimbangan cair-cair UNIFAC. Kemudian campuran PP-MNR dianalisa dengan uji difference scanning calorimetry (DSC). Hasil uji DSC digunakan untuk melakukan validasi hasil perhitungan kesetimbangan cair-cair UNIFAC. Hasil perhitungan UNIFAC merupakan kesetimbangan cair-cair sistem PP-MNR berupa kadar MNR dan temperatur proses pencampuran. Pada campuran ini MNR berfungsi sebagai compatibilizer. Kadar MNR pada campuran adalah 4,4%–11,16% dan temperatur proses adalah 170 o C–210 o C. Semakin besar kadar MNR dalam campuran, semakin rendah suhu proses pencampuran. Hasil validasi uji DSC sesuai dengan prediksi kesetimbangan cair-cair sistem PP-MNR menggunakan metode UNIFAC.

Thermoreversible cross-linking of maleated natural rubber with glycerol

In this article, thermoreversible covalent cross-linking of maleated natural rubber (MNR) with glycerol was studied. Firstly, NR was grafted with maleic anhydride using a reactive processing method. The result showed that MNR was successfully obtained without the addition of initiator. The highest grafting was 1.76%. Secondly, the obtained MNR was dissolved in toluene and then mixed with glycerol, which is used in this study as the thermoreversible cross-linking agent. Fourier transform infrared spectra of the casted MNR film mixed with glycerol showed that upon heating, covalent ester cross-links were formed via the reaction of succinic anhydride ring with hydroxyl groups of glycerol. The swelling test indicated that the swelling index (%) decreased with increasing glycerol loading. This indicated that the degree of cross-linking directly depended on the amount of glycerol. The tensile strength and modulus were significantly improved upon increasing the level of cross-linking. The MNR cross-linked with glycerol can be remolded at 150°C more than three times. After remolding, the mechanical properties decreased with increasing recycling round.