Composition of fresh natural rubber latex (NRL) and centrifuged latex.
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JRLDR
SHENZHOU
Fresh latex is obtained from a rubber tree by tapping (cutting) a bark, and it is collected into a special cup installed on a tree (Figure 1). Making correct incising requires knowledge, precision, and experience. It has to be done carefully and not too deep to avoid damage of a tree. Vessels with latex run spirally in clockwise direction up the tree. Optimal way of tap is from high left- hand to low right hand, which maximizes the number of the opened vessels . These actions have to be carried out early in the morning, when tree “gives” more latex sap due to the greatest turgor of cells during relatively lower transpiration (high humidity and low temperature). On the other hand, in morning conditions, evaporation is lower and latex can stay longer as a stable liquid.
Tapped Hevea brasiliensis rubber tree and fresh latex collecting.
Fresh field latex is a sensitive material, and it coagulates within a few hours after leaving the tree. Fresh latex has different composition than on the next steps of processing (Table 1). First of all, it has lower concentration of the rubber material: depend on the clone, it is 30–35% [5]. It has also high variety of non-rubber substances. Characteristics for fresh latex only are, e.g., lutoids. These are vacuolar structures surrounded by a phospholipid membrane containing, among others, significant amounts of proteins [12]. Neutral pH 6–7 and relatively high number of organic compounds, like carbohydrate, make fresh latex sensitive to bacterial growth and putrefaction. Therefore, it is crucial to protect it by the proper preservation.
| Constituents | Fresh latex [%] | Centrifuged latex [%] |
|---|---|---|
| Water | 59,5–66 | 38,5–39 |
| Rubber | 30–35 | min. 60 |
| Non-rubber substances (total) | 4–6,5 | max. 1,7 |
| Proteinaceous substances | 1–1,5 | |
| Resinous substances | 1–2 | |
| Carbohydrates | 1 | |
| Mineral matter | 1 |
Composition of fresh natural rubber latex (NRL) and centrifuged latex.
From the practical and commercial point of view, latex for onward transport to downstream users has to be concentrated. Concentration is a process of increasing the amount of rubber in the latex. According to the accepted standards, the concentrated latex should contain minimum 60% of rubber.
One of the most popular and effective concentrating methods is centrifuging (Figure 2). The method uses the difference in density (specific gravity) of the rubber compared to the density of the serum (water phase). The weight of serum (1,02 g/ml) with non-rubber substances is higher than the weight of a rubber (0,92 g/ml). Latex in a centrifugal separator is subjected to high centrifugal force on plates and separated in two fractions: concentrated latex and skim latex. During the process, these two materials go different ways inside the machine to two different outlets. The efficiency of centrifuging process is 85–90% , which means skim latex is also a usable material with 2,5–10% of rubber content. Skim fraction can be coagulated and used as a source of dry rubber (skim rubber in blocks or crepe).
Fresh latex is obtained from a rubber tree by tapping (cutting) a bark, and it is collected into a special cup installed on a tree (Figure 1). Making correct incising requires knowledge, precision, and experience. It has to be done carefully and not too deep to avoid damage of a tree. Vessels with latex run spirally in clockwise direction up the tree. Optimal way of tap is from high left- hand to low right hand, which maximizes the number of the opened vessels . These actions have to be carried out early in the morning, when tree “gives” more latex sap due to the greatest turgor of cells during relatively lower transpiration (high humidity and low temperature). On the other hand, in morning conditions, evaporation is lower and latex can stay longer as a stable liquid.
Tapped Hevea brasiliensis rubber tree and fresh latex collecting.
Fresh field latex is a sensitive material, and it coagulates within a few hours after leaving the tree. Fresh latex has different composition than on the next steps of processing (Table 1). First of all, it has lower concentration of the rubber material: depend on the clone, it is 30–35% [5]. It has also high variety of non-rubber substances. Characteristics for fresh latex only are, e.g., lutoids. These are vacuolar structures surrounded by a phospholipid membrane containing, among others, significant amounts of proteins [12]. Neutral pH 6–7 and relatively high number of organic compounds, like carbohydrate, make fresh latex sensitive to bacterial growth and putrefaction. Therefore, it is crucial to protect it by the proper preservation.
| Constituents | Fresh latex [%] | Centrifuged latex [%] |
|---|---|---|
| Water | 59,5–66 | 38,5–39 |
| Rubber | 30–35 | min. 60 |
| Non-rubber substances (total) | 4–6,5 | max. 1,7 |
| Proteinaceous substances | 1–1,5 | |
| Resinous substances | 1–2 | |
| Carbohydrates | 1 | |
| Mineral matter | 1 |
Composition of fresh natural rubber latex (NRL) and centrifuged latex.
From the practical and commercial point of view, latex for onward transport to downstream users has to be concentrated. Concentration is a process of increasing the amount of rubber in the latex. According to the accepted standards, the concentrated latex should contain minimum 60% of rubber.
One of the most popular and effective concentrating methods is centrifuging (Figure 2). The method uses the difference in density (specific gravity) of the rubber compared to the density of the serum (water phase). The weight of serum (1,02 g/ml) with non-rubber substances is higher than the weight of a rubber (0,92 g/ml). Latex in a centrifugal separator is subjected to high centrifugal force on plates and separated in two fractions: concentrated latex and skim latex. During the process, these two materials go different ways inside the machine to two different outlets. The efficiency of centrifuging process is 85–90% , which means skim latex is also a usable material with 2,5–10% of rubber content. Skim fraction can be coagulated and used as a source of dry rubber (skim rubber in blocks or crepe).
