Impact of Industrial Source on the Chemical Composition of Loblolly Pine Bark

The chemical compositions of loblolly pine (Pinus taeda L.) bark samples from two industrial sources were determined for whole bark as well as the inner and outer bark components. Differences in extractive contents of the whole bark samples were primarily attributed to the different debarking methods which afforded different proportions of inner and outer bark. Treatment of the extractive-free bark samples with 1 percent NaOH to remove interfering phenolic compounds impacted the lignin contents determined by the Klason method, but not those determined by the acetyl bromide method. Upon determining the proportions of inner and outer bark, the data provided here can be used to estimate the chemical compositions of other southern yellow pine bark resources. Most bark residues currently generated by the forest products industry sector are burned as fuel. Therefore, while the processing of southern yellow pine (SYP) timber affords large volumes of bark, little of this biomass resource is wasted. Concerns have been raised about reductions in fuel value from deterioration and process problems from high moisture and ash contents. Recently, inquiries about the use of SYP bark as a source of extractives have increased. Interest has also been expressed in recovering value from the structural polymers (lignin, cellulose, hemicelluloses) comprising extractive-free bark residues. Literature reports validate that there is continued interest in bark characterization with the ultimate objective(s) of developing chemical products such as nutraceuticals, adhesives, and biofuels (Ingram et al. 2008, Sxen et al. 2010, Ku et al. 2011). A variable with industrial bark supplies that can bring consternation is the proportion of outer bark (rhytidome) and inner bark (phloem). In a prior study, outer:inner bark ratios were 5.8 and 1.5 from loblolly pine (Pinus taeda L.) bark residues collected from a plywood plant and paper mill, respectively (Eberhardt et al. 2009). These different ratios reflect both the differences in the sizes of the logs being processed and the debarking methods. Whereas ring debarking at the plywood plant afforded large pieces of relatively intact bark, drum debarking at the paper mill afforded stringy pieces of inner bark with less outer bark, the latter being highly abraded (Eberhardt and So 2005). In the present study, chemical composition data for these two bark supplies are reported. Differentiating these data from those in the literature (McGinnis and Parikh 1975, Labosky 1979, Huang et al. 2011) are values for the inner and outer bark components; also, lignin contents are from direct determinations and not simply calculated by difference (Pearl and Buchanan 1976). The primary objective of this very brief report is to provide updated chemical composition data that can be used as a practical reference to direct new utilization ventures toward potential SYP bark suppliers in the forest products industry sector. Materials and Methods Bark collection and processing Bark samples were obtained from two local forest products companies (plywood plant, paper mill) processing loblolly pine logs. It should be noted that in such industrial settings, there is the distinct possibility of some bark from the other southern yellow pines being included. Whole bark samples were ground as received with drying under ambient conditions. Essentially debris-free inner and outer bark samples were prepared by carefully peeling bark chips/ strands by hand before freeze-drying. All bark samples were ground to pass a 2-mm-mesh sieve plate before extraction.