GENERATIONS OF VOCS FROM PAPER DUE TO PULPING, BLEACHING, PAPERMAKING ADDITIVES AND ITS EFFECTS ON NATURAL AGING OF PAPER

Abstract

The study involved the identification of volatile organic compounds (VOCs), specifically aldehydes, that are emitting from paper (unbleached and bleached). The mechanical strength properties of paper, which might be affected by the morphological characteristics of cellulose fibers over time were also considered. Pulp from the integrated mill revealed the presence of pre-existing VOCs like aliphatic hydrocarbons and aldehydes in the samples. Over the course of aging under ambient conditions, observation reveals the generation of acid-functionalized VOCs within the paper. This generation of VOCs was confirmed through ATR-FTIR analysis, which indicated an increase in the intensities of peak absorbance around 3340 cm−1 and 1641 cm−1. These peaks correspond to the –OH stretching of acidic functional groups and the C=O stretching of aldehyde and acidic functional groups. The impact of aging on the degree of polymerization (DP), a critical factor influencing paper strength was studied on unbleached and bleached pulp, which demonstrated that DP was decreased over time. In addition to this the strength properties of unbleached and bleached paper, including the tensile index, exhibited reductions of approximately 12 and 29%, while the burst index experienced decreases of approximately 24 and 42%, respectively. Intermediate bleaching stages also experienced a decline in strength properties and optical properties over time. Laboratory experiments were also conducted to study the generation of volatile organic compounds and the impact of natural aging on the strength properties of both unbleached and bleached pulp. According to the existing literature extractive and metal ions are major sources to produce volatile organic compounds due to auto-oxidation. Thus, acid treatment of the raw material was conducted before making pulp to remove the extractives and metal ions. Treatment at optimized conditions (pH- 2, consistency %, retention time- 1hr) effectively reduced metal ion and extractives content by approximately 50% with the benefits of pulping yield, strength properties of paper, and the reduction in VOC generations. For Mechanical, Kraft, and Soda paper, there was a reduction of approximately 52, 51, and 28% in Hexanal emissions, respectively. Additionally, Nonanal emissions decreased by approximately 35, 64, and 8.3% for the corresponding paper types. The acid treatment of the material also led to a decrease in the demand for active alkali of about 3 % during pulp production in comparison to the untreated material. Despite chemical savings higher pulping yield of about 6-7% was also observed. Furthermore, the acid treatment resulted in improved cellulose fiber characteristics, including, a greater crystallinity index, and a higher degree of polymerization. These modifications contributed to the improved strength properties of paper, such as increased tensile, tear, and burst strength. Various raw materials were examined to study VOC generation, with agro-based sources like wheat straw and rice straw emitting a higher quantity of VOCs in comparison to hardwood pulp. Various pulping methods were employed to assess VOC generation, and the findings confirmed that Hexanal, Octanal, and Nonanal were consistently produced from all types of pulp, with the exception of furfural, which was specifically generated from mechanical pulp. Observations indicate that VOC generation from unbleached paper follows the following pattern.