**2. Deproteinized natural rubber**

*Silicon Materials*

Akron abrasion (mm3

*a*

*b*

**Table 1.**

**Properties sSBR/BR\* sSBR/BR\* ENR**

**Properties 50 phr carbon blacka 50 phr silicab**

Tensile strength, MPa 29 26 25 24 21 27 Elongation at break, % 495 435 500 720 405 435 M300, MPa 12 12 13 6 13 13 Hardness, IRHD 65 69 73 69 67 68 Compression set 24 h/70°C, % 18 17 21 32 18 22

Heat buildup, ΔT, °C 7 7 23 47 7 19

*Rubber formulation in phr: rubber 100, filler, oil 5, ZnO 5, StA 2, antioxidant 2, S 2, MBS 1.5.*

*Comparison of physical properties of black and silica-filled ENR vulcanizates.*

*Rubber formulation in phr: rubber 100, filler, oil 5, ZnO 5, StA 2, antioxidant 2, S 2, MBS 1.5, DPG 0.5.*

/500 rev) 21 14 11 63 15 14

Filler (phr) 80 80 67.5 50 Tensile strength, MPa 16 20 19 24 Elongation at break, % 780 515 600 550 M300, MPa 3.9 8.4 7.6 9.5 Hardness, IRHD 82 62 65 63 Angle tear, N/mm 39 36 43 40 Akron abrasion, vol loss, mm3 41 13 12 <20 Dunlop resilience, % 44 55 38 67

*Comparison of physical properties of ENR-silica and sSBR/BR tread compounds.*

**Properties ENR-sulfur vulcanizate** 

admicellar polymerization, a bilayer of surfactant (admicelle) is formed on the surface of silica and polymerization of the monomer in the admicelle resulting in an ultrathin layer of polymer covering the silica [33, 36, 37]. The silica modified with admicellar polymerization has superior performance compared to those reinforced

**(no silane)**

Silica content (%) 27 28 27 Tensile strength, MPa 12 19 16 Elongation at break, % 390 290 300 M100, MPa 2 7 5

with unmodified or silica modified with typical coupling agents [37].

*Comparison of tensile properties of ENR-silica sulfur cured with ENR-APS sol-gel system.*

**Silica Silica-TESPT Black N234 Silica**

**ENR-APS sol-gel ENR-APS** 

**sol-gel**

**NR ENR25 ENR50 NR ENR25 ENR50**

**48**

*\*70/30.*

**Table 2.**

**Table 3.**

Purification of natural rubbers from nonrubber components is possible especially the protein removal. The deproteinization process of natural rubber yields a rubber with reduced protein content significantly as well as low ash and volatile matter which is known as deproteinized natural rubber (DPNR). The deproteinization process can be carried out with natural rubber latex via enzymatic treatment [38–40] or urea treatment [41, 42]. The principle of deproteinization with enzymatic treatment is to hydrolyze the proteins in the natural rubber latex into water soluble which will be removed during washing process of manufacturing the rubber [41, 42].

Structural changes of NR branch points are proposed to occur with the deproteinization process [15]. This is based on the findings that a linear rubber chain contains two types of functional groups at both terminals. After deproteinization, the branch points formed by the functional groups associated with proteins at the α-terminal through hydrogen bonding decompose and leave the branch points from phospholipid at the α-terminal. The long-chain branching in the purified NR originated from the interaction of phospholipids which link the rubber chain together [43–45]. The phospholipids are associated together by the formation of a micelle structure.

The commercially available DPNR is Pureprena, which is produced by the Malaysian Rubber Board and licensed to Felda Rubber Industries Sdn Bhd. Pureprena is a purified form of natural rubber and has a very-low-nitrogen, ash, and volatile matter contents as well as being lighter in color (**Table 4**). DPNR is less prone to storage hardening than a normal NR grade. When compounded using an efficient vulcanization (EV) system, DPNR has low creep and stress relaxation, low water absorption, low compression set, and a more consistent modulus when subjected to variable humidity conditions [46]. DPNR gives superior rubber compounds with excellent dynamic properties which are suitable for engineering applications (**Table 5**) [46].


**Table 4.**

*Comparison of raw rubber properties specification of DPNR (Pureprena) and natural rubber (SMR20).*


#### **Table 5.** *Areas of application of DPNR.*
