Introduction
Skim natural rubber latex is a by-product of centrifugation process used to prepare concentrated natural
rubber latex. The usual method used to recover rubber particles from skim latex is coagulation by concentrated
sulfuric acid. However, the acid influences on quality of the skim rubber and leads to highly acidic effluent which
impacts on environmental pollution. It has been reported that removing of protein from skim latex either by
centrifuging or enzyme hydrolysis caused increasing capability to coagulate the skim latex (Bunrasri., 1999).
Furthermore, recovering a residual rubber by using the hydroxypropyl methylcellulose (HPMC) caused decreasing
effluent acidity and sulfate ion in serum lower than that of using concentrated sulfuric acid (Nitayapat
et al
, 2008).
Furthermore, application of water soluble chitosan with the adjustment of pH to be neutral seemed to increase the
performance of the coagulation-flocculation process of the skim latex (Werathirachot
et al
., 2008). Creaming of skim
latex by cellulose ethers was also used to prepare good quality skim rubber. It found that efficiency of creaming
process did not depend on source, age and ammonia content of the skim rubber latex (Dokkhan., 2008). Recently,
polyelectrolyte in form of poly (methyl acrylic ester) cationic polymer coagulant showed higher coagulation efficiency
than that of poly (acrylamide) anionic polymer coagulant (Phupewkeaw., 2009).
This works was aimed to investigate the influence of ammonium polyacrylate solution (NHPA) on
coagulation of skim natural rubber latex with various incubation time.
Material & Methods
Materials
Acrylic acid (Aldrich, 99%), ammonium hydroxide solution (Merck, 25%) and potassium persulfate (Fluka,
98%) were analytical grade, and used without further purification. Sulfuric acid (Lab-Scan, 98%) was analytical
grade, and used as received.
Preparation of ammonium polyacrylate solution (NHPA)
Ammonium polyacrylate (NHPA) was prepared by gently dropping 20 wt% ammonium hydroxide solution
(0.2 mol, 38.5 g) to acrylic acid (0.2 mol, 14.4 g) under cooling condition. The acid-base reaction was
potentiomerically monitored to achieve a complete neutralization. Just before polymerization, monomer solution was
poured into a 500 ml glass reactor fitted with a mechanical stirrer, a condenser, a thermometer and controlling system
temperature at 70
°
C by a circulation water bath. The reaction was initiated by addition of potassium persulfate (0.02
g) into the reactor under stirring speed of 100 rpm. Then, distilled water (100 ml) was added to the reactor. The
reactions were proceeded for 1, which color of the solution changed from colorless to light orange. After being cooled
to room temperature, the solution was poured into beaker and diluted to 10 wt% with distilled water.
The reaction
product was eventually analyzed by FT-IR.
Characterizations
FTIR (Nicolet MAGN-IR 560 spectrophotometer) with a resolution of 4 cm
-1
and wavenumbers of 400-4000
cm
-1
was used to identify chemical structure of the ammonium polyacrylate (NHPA). Furthermore, size of rubber
