Geographical variations and correlation among some chemical and thermal properties of Almaciga (Agathis philippinensis Warb.) resins from selected commercial sites in the Philippines

Abstract

Almaciga (Agathis philippinensis Warb.), a tropical conifer that is tapped for its resin commercially known as Manila copal, grows in many parts of the Philippines, but resin buyers prefer and pay a better price for resin from southern Palawan. The study was done to characterize almaciga resins obtained from commercial sites in Davao Oriental and Palawan (Brooke's Point and Marufinas) to explain the quality and price differences. Fresh and aged resin samples were subjected to wet chemical, thermal, and spectral analyses. Generally, the resin samples were found to be soluble in the more polar solvents although significant variations were observed for resins from various sites. Titrimetric determination revealed no significant variation in acid and saponification values, although the Brooke's Point resin had significantly lower unsaponifiable components. Predominant Fourier transform infrared spectroscopy (FTIR) absorption peaks for fresh resin include strong C=O stretch and weak = C–H stretch. Aged Palawan resins, which showed increased solubility in polar solvents, exhibited increased intensity of prominent FTIR peaks such as O–H stretch and C=O stretch. The weak peak at 1719 cm−1 seen in fresh Palawan resins was no longer observed in aged resins. DSC revealed the semi-crystalline nature of almaciga resin and melting temperatures similar to diterpenoid resin acids. This is attributed to the presence of increasing amounts of oxidized abietic acids as shown by gas chromatography-mass spectrometry (GCMS). For the Davao Oriental resins, significant amount of agatholic acid was shown, while resin acids of the abietane and pimarane type were conspicuously absent in the GC-MS spectrograms. The study found evidence that almaciga resins from Davao and Palawan differ in chemical composition and physical properties, which could explain the quality and price differences.