**5. Conclusions**

Deproteinized natural rubber is a purified form of natural rubber, which is characterized by its very low nitrogen, ash, and volatile matter contents compared to the commercial natural rubber. Similar to natural rubber, DPNR can be reinforced with carbon black as well as silica according to the intended applications.

DPNR reinforced with carbon black filler has low creep and stress relaxation, low water absorption, low compression set, and a more consistent modulus. Carbon

**63**

**Author details**

Siti Salina Sarkawi

Sg Buloh, Selangor, Malaysia

provided the original work is properly cited.

\*Address all correspondence to: ssalina@lgm.gov.my

*Silica-Reinforced Deproteinized Natural Rubber DOI: http://dx.doi.org/10.5772/intechopen.85678*

engineering applications.

black-filled DPNR exhibits excellent dynamic properties which are suitable for

Reinforcement of DPNR by silica filler is different from carbon black as silane coupling agent is required. Mixing temperature has a dominant effect in mixing DPNR and silica as well as NR and silica in the presence of a coupling agent. NR suffers some loss of dynamic and mechanical properties due to thermo-mechanical degradation when mixed at above optimum mixing temperature of approximately 155°C. On the other hand, DPNR shows a smaller influence of dump temperature and more constant mechanical properties. Higher silica-silane-rubber coupling in DPNR-silica-TESPT compounds is shown with improvement in the dynamic properties especially the lower tan δ at 60°C which indicates the lower rolling resistance of tire. The dispersion morphology of silica and rubber-to-filler interaction in DPNR is elucidated by atomic force microscopy and TEM network visualization.

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Malaysian Rubber Board, Rubber Technology Centre, RRIM Research Station,

## *Silica-Reinforced Deproteinized Natural Rubber DOI: http://dx.doi.org/10.5772/intechopen.85678*

*Silicon Materials*

**Figure 14.**

*with silane coupling agent, TESPT.*

polystyrene is the unstained part. Some silica aggregates in silica-filled NR are surrounded by voids or vacuoles, and some have connecting network strands to the NR network. This indicates there exist some bondings of silica to the rubber networks. This observation is totally different with the network visualization of the silica-filled DPNR. The silica aggregates in the DPNR system without silane have clear vacuoles surrounding them [62]. The vacuoles are formed through polymerization of styrene in the gap between the silica aggregates and the rubber chain. The formation of such vacuoles is due to a weak interface between silica particles and rubber chains [66]. The weak filler and rubber interaction in the system without silane is derived from the silica characteristic of surface energy with low dispersive component, ɤsd, which results in less adsorption of rubber chains to the surface of the silica. There are less vacuoles present in the NR vulcanizate as compared to the DPNR vulcanizate without silane, which suggests higher filler-

*Comparison of TEM network visualization micrographs of silica-filled (a) NR and (b) DPNR vulcanizates* 

A comparison of the TEM network visualization between NR and DPNR vulcanizates with TESPT coupling agent included is shown in **Figure 14**. The presence of TESPT results in strong attachment of rubber chain to the surface of silica aggregates. No sign of vacuoles present in the system after network visualization. This is due to the establishment of chemical bonding between silica-TESPT-rubber in the compound during silanization and vulcanization. In addition, the size of silica aggregates in both NR and DPNR with TESPT is smaller than those without TESPT. This relates to the results of low Payne effect and high chemically BRC for NR and DPNR reinforced with silica and silane system. In addition, the vulcanizates with silanes exhibit denser rubber network compared to those without silane. This is in agreement with the results of cross-link density where the silica-filled NR and DPNR with TESPT have higher cross-link density compared to those without

Deproteinized natural rubber is a purified form of natural rubber, which is characterized by its very low nitrogen, ash, and volatile matter contents compared to the commercial natural rubber. Similar to natural rubber, DPNR can be reinforced with

DPNR reinforced with carbon black filler has low creep and stress relaxation, low water absorption, low compression set, and a more consistent modulus. Carbon

carbon black as well as silica according to the intended applications.

to-rubber interactions in the former.

silane due to sulfur released from TESPT [62].

**62**

**5. Conclusions**

black-filled DPNR exhibits excellent dynamic properties which are suitable for engineering applications.

Reinforcement of DPNR by silica filler is different from carbon black as silane coupling agent is required. Mixing temperature has a dominant effect in mixing DPNR and silica as well as NR and silica in the presence of a coupling agent. NR suffers some loss of dynamic and mechanical properties due to thermo-mechanical degradation when mixed at above optimum mixing temperature of approximately 155°C. On the other hand, DPNR shows a smaller influence of dump temperature and more constant mechanical properties. Higher silica-silane-rubber coupling in DPNR-silica-TESPT compounds is shown with improvement in the dynamic properties especially the lower tan δ at 60°C which indicates the lower rolling resistance of tire. The dispersion morphology of silica and rubber-to-filler interaction in DPNR is elucidated by atomic force microscopy and TEM network visualization.
