Phospholipids and proteins were separately removed as the main non-rubber components to individually study their effect on the structure and properties of the rubber. Fourier Transform Infrared Spectroscopy (FTIR) and 1H nuclear magnetic resonance spectroscopy (1H-NMR) were used to characterize the chemical structure and the residual non-rubber component. A rheology study and stress relaxation measurements were used to study the role that non-rubber components play in natural networks. A rheological study showed that natural rubber (NR) and deproteinized natural rubber (DPNR) exhibited similar dynamic modulus at 170 °C. The lack of superposition in van Gurp–Palmen (vGP) curves at different temperatures for NR and DPNR, together with the shape of vGP curves, proved that long chain branching was mainly constructed by phospholipids. Stress relaxation measurements at room temperature were fitted with the Maxwell model and showed that the NR relaxation curve underwent a quick decrease and then came to an equilibrium stress retention of 58%, which is about 3 times higher than that of DPNR, indicating that proteins in NR contributed to the network structure at room temperature. Combining molecular dynamic studies, the interaction of proteins and phospholipids in non-rubber networks was proposed.

Thermal oxidative ageing process of commercial available styrene–butadiene random copolymer (SBR) has been studied by the combination use of in-situ collected dynamic FTIR spectrum and two dimensional correlation analysis. The modification on the viscoelastic properties were studied by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). It was found that the degradation took place predominantly in the aliphatic segment at the allylic position, giving rise to a maximum absorption at 1725 cm−1 in the carbonyl stretching region. The initiation process occurring in the aromatic parts produced acetophenone end groups as evidenced by the shoulder peak at 1679 cm−1. A series of oxygenated species were identified in the dynamic spectrum including anhydrides, lactones, peracids, aliphatic ketones and unsaturated carbonyl species. However, the band of unsaturated carbonyl species at 1695 cm−1 varied nonmonotonously, first increase sharply and then decreased. Concerning the concentration of double bonds, a detailed analysis revealed the different evolving trend between benzylic and aliphatic vinyls. The former showed an increment whereas the later were found to decrease, resulting in the broadening at 1638 cm−1. Furthermore, the relative generation rates of different carbonyls were ranked by two dimensional correlation analysis together with two shoulder peaks at 1713 and 1679 cm−1 identified subtly in the asynchronous spectrum. On the basis of the above spectroscopic results, the mechanisms of thermal degradation were proposed.The relaxation behavior of thermally degraded SBR was studied by DMA and DSC. Both of the two techniques evidenced an increasing and broadening Tg, suggesting the crosslinking reaction dominated thermal degradation. After checking the normalized spectra, it is found that all of the relaxation curves (irrespective of storage modulus, loss modulus or loss tangent) get widen over ageing. Two parameters, steepness (S) and wideness index (W) were defined in normalized storage modulus plot to make a quantitative discussion. The S reduced whereas the W rose up after degradation. The broader glass transition zone after ageing was attributed to the more heterogeneous relaxation environment and the wider size distribution of motion units participating in the transition.