Microstructure and Lamellae Phase of Raw Natural Rubber via Spontaneous Coagulation Assisted by Sugars

Abstract

Natural rubber (NR) as a renewable biopolymer is often produced by acid coagulation of fresh natural latex collected from Hevea brasiliensis. However, this traditional process is facing a huge economic and environmental challenge. Compared with the acid coagulation, spontaneous or microorganism coagulation is an ecofriendly way to obtain NR with excellent performance. To clarify the influence of different sugars on NR quality, several sugars were used to assist the coagulation process. Influence of different sugars on microstructure and cold crystallization were examined by 1H NMR, DSC, etc. The results indicated that sugars exhibit different biological activity on terminal components of fresh field latex and can influence the resultant molecular structure and basic properties. Brown sugar exhibits higher metabolic activity and is inclined to decompose the protein and phospholipids crosslinking compared with other sugars. The larger molecular weight of sugar molecule is beneficial for the formation of the stable α lamellae phase and higher overall degree of crystallization.

Mechanism of the green coagulation processes on the construction of raw rubber network structure

“…Liu et al 15 demonstrated that the natural network of NR is formed by linking polyisoprene chains to proteins and phospholipids. Coagulation is a very important step in the preparation of raw rubber from NRL, and the coagulation method affects the subsequent performance of the rubber composites 16–20 . Different coagulation processes of latex result in different networks and structures of raw rubber, leading to differences in the performance of raw rubber and vulcanized rubber.…”

An environmentally friendly and efficient technology to prepare high‐performance natural rubber: Electrophoretic coagulation

“…At present, acid coagulation is the most common coagulation method, which is applied to produce commercial NR such as standard rubber and ribbed smoked sheets. 12,13 But the addition of acid might damage some of the effective components of the NRL, which would deteriorate the properties of NR. 14 And during the production process, the low efficiency, harsh environment production, and huge labor intensity will seriously damage the health of workers and pose a severe threat to the environment.…”

“…NR is obtained by coagulation from natural rubber latex (NRL). At present, acid coagulation is the most common coagulation method, which is applied to produce commercial NR such as standard rubber and ribbed smoked sheets 12,13 . But the addition of acid might damage some of the effective components of the NRL, which would deteriorate the properties of NR 14 .…”

On the influence of the amorphous phase on the stability of crystals in poly(cis‐1,4‐isoprene) networks

“…Crystals in natural rubber (NR) networks are a good example of this polymer‐typical characteristic, 5 because they form at room temperature only under strain but spontaneously melt when the stretching force is released and the rubber retracts back to its original dimensions. This phenomenon, referred to as strain‐induced crystallization (SIC), is intensively studied since its discovery in the 1920s, because it is assumed to be responsible for the outstanding high tensile strength of NR at high elongations 6–19 …”

“…This is the reason, why polymers with lamellar morphology principally cannot escape from high surface-to-volume ratios and exhibit melting temperatures T m that are distinctly lower than the thermodynamic equilibrium melting temperature T m 0 . Knowing the energy of the refolded crystal surface, the deviation of T m from T m 0 can be calculated from L using the Gibbs-Thomson equation 2À4 Crystals in natural rubber (NR) networks are a good example of this polymer-typical characteristic, 5 because they form at room temperature only under strain but spontaneously melt when the stretching force is released and the rubber retracts back to its original dimensions. This phenomenon, referred to as strain-induced crystallization (SIC), is intensively studied since its discovery in the 1920s, because it is assumed to be responsible for the outstanding high tensile strength of NR at high elongations.…”