0101-A2

The Possible Development of Phenol-Formaldehyde Glue Derived From the Distilled Black Liquor

R. Sudradjat and Han Roliadi ¹

Abstract

There has been a significant development of pulp and paper industries in Indonesia during the last decade. At least two million tons of paper are produced annually using particular raw materials, e.g. fast-growing wood species, bamboo, straw, and waste paper. There also occur a significant growth in income and the widening opportunity of labor employments at national level. Unfortunately, in the environmental point, the black liquor generated from the pulp/paper processing which so far is only discharged or disposed causes the concern, due to the toxicity of the phenol compounds it contains. It has been noted that about 13,000 tons of black liquor with 18-% consistency is just discharged with the concurrent production of 15,000 tons of pulp (dry basis).

This experiment was aimed at looking into appropriate method to recuperate the problems of black liquor's phenol by further converting it to the most valuable glue largely and extensively used in the plywood industries, i.e. phenol-formaldehyde. The experiment was divided into three respective stages, i.e. (a) recovery of phenol from black liquor, after being initially distilled; (b) selecting phenol compounds from another source as additive to increase the existing phenol concentration in the distilled black liquor; and (c) working out optimum phenol concentration able to develop maximum bonding strength of the phenol-formaldehyde glue.

It turned out that the recovery of phenol from the distilled black liquor was low (i.e. 12%). Phenol crystal (p.a) as selected performed better than tannin as chemical additive to increase low phenol concentration in the black liquor as shown by the improvement in the plywood properties. The optimum ratio of phenolic crystal additive to the distilled black liquor was 1:15 (w/w). The maximum bonding strength of plywood assembled using phenol-formaldehyde glue formulated from the mixture of distilled black liquor and phenolic crystal was 24.0 kg/cm ² . This figure complied with the Indonesian Industrial Standard for plywood's bonding strength (i.e. 14.0 kg/cm ² ).

I. Background and Significance

Black liquor is a spent liquid waste that is drained off after the cooking stage in the chemical pulping process, predominantly kraft, sulfite, and soda ones. Concurrently, in this way, the draining is intended to separate the cooked (softened) wood material from the black liquor. The black liquor can contain dissolved organic woody material (e.g. removed extractives, degraded carbohydrate, phenolic compounds, etc.) and residual cooking-chemical compounds, and is therefore usually toxic. Unlike black liquor from the kraft and sulfite processes, the one from the soda process is usually not recovered of its cooking chemicals and instead just dumped or drained to land fill or water bodies (e.g. lakes, rivers, or seas). The phenolic compounds that are formed from the degradation of particular wood chemical component (i.e. lignin) during the pulping are suspectedly blamed for toxicity of the sulfite's black liquor. Consequently, most communities are opposed to the discarding of such black liquor, since they are feared of its negative impacts on their life and environments.

The toxic suspected phenolic compounds are in fact a valuable stuff that can be theoretically converted to high-priced or expensive phenol formaldehyde compound. Phenol formaldehyde has been commonly and largely used as popular glue in plywood industries.

Inherent with such, a research/experiment had been proposed to assess whether the phenolic compounds in the soda's black liquor could be isolated/separated for their further conversion into phenol formaldehyde, which was subsequently developed as valuable glue in the plywood manufacture/fabrication. The related details of procedures and results of this experiment are forthcoming.

II. Material and Methods

A. Materials

The black liquor used as a sample in this experiment was the cooking waste taken from a pulp/paper mill which employed soda chemical process, situated in Bandung (West Java). Other chemicals as also used were tannin, phenol crystals, and formaldehyde crystals.

B. Methods

1. Isolation/extraction of phenol compounds from the soda's black liquor

• Black liquor was initially made more alkaline by the addition of particular amount of technical NaOH solution until its pH reached about 10.
• Then as much as 10 ml of the NaOH-added black liquor was taken and subjected to fractional distillation
• The distillation duration was regulated until approximately 200 ml of distilled black liquor solution was obtained/collected
• The distilled black liquor was further placed in a special container and then underwent particular qualitative analysis for the determination of phenol compounds. In this way, the phenol content and recovery based on the original soda's black liquor could be determined

2. Concentrating the distilled black liquor

• The distilled black liquor was concentrated by refluxing it under mild heat. The concentrated distilled black liquor could then be regarded roughly as phenol
• The phenol (concentrated distilled black liquor) was subsequently mixed with tannin crystals at three ratios (w/w), i.e. consecutively 1:3, 1:5, and 1:7. The mixture at each ratio was thoroughly agitated until becoming homogenous. Meanwhile, the phenol was also separately mixed with phenol crystals, at the three ratios (w/w) as well similar to the ones as for the tannin crystals
• The mixtures either between phenol and tannin crystal or between phenol and phenol crystal, at each of the three ratios, was reacted with formaldehyde at the respective portion 1.0: 1.2 (w/w). In this way, phenol formaldehyde would be formed and used in the further experiment as glue in the fabrication/assembling of plywood. The resulting plywood was subsequently tested of its strength and other related properties, which covered moisture content and density of plywood, and bonding strength of the glue line (body) in the plywood assembly .
• It turned out that the strength of plywood bonded with the phenol formaldehyde glue where the phenol was mixed with tannin crystal was significantly lower than the one where the phenol was mixed with phenol crystal. Hence, the phenol crystals were preferred as an additive to make more concentrated the dilute phenol concentration in the distilled black liquor. The mixture of the distilled black liquor and phenol crystals was subsequently reacted with formaldehyde for the formulation of phenol formaldehyde glue, which was further used in the bonding experiment of plywood.

3. The manufacture of plywood employing phenol-phenol crystal-formaldehyde glue

• In this experiment, the mixing ratios between phenol crystals and the distilled black liquor were arranged in four levels (w/w), i.e. consecutively 1:10, 1:15, 1:20, and 1: 25. The intent was to figure out which ratio(s) could brought out the plywood, in the further bonding experiment, with the most satisfactory (strength) properties
• The mixtures between phenol crystal and the distilled black liquor at their particular ratios were each reacted separately with formaldehyde to form phenol formaldehyde
• The resulting phenol formaldehyde was further used a glue in the bonding experiment for plywood manufacture/assembling. The plywood was subsequently tested of just its bonding strength

4. Data analysis

The experiment on manufacturing plywood which employed the use of each of the four mixing ratios as such between phenol crystals and the distilled black liquor was replicated four times. The resulting data on plywood property (i.e. just bonding strength) were analyzed using completely randomized design with one-way classification. In this regard, the class (single factor) was the inherent mixing ratios. Meanwhile, the plywood manufacture which implemented the use of mixtures either between the concentrated distilled black liquor and tannin crystals, at particular ratios; or between the concentrated distilled black liquor and phenol crystal, also at similarly particular ratio, was replicated four times as well. The one-way classification was used as well to analyze the resulting data of such plywood (i.e. moisture content, density, and bonding strength). For this case, the factor was the mixing ratios between the concentrated distilled black liquor and tannin crystals as well as between the concentrated distilled black liquor and phenol crystals.

III. Results and Discussion

1. Recovery of phenol; the concentration of phenol in the soda's black liquor, before being distilled, was relatively low, i.e. 2898.3 ppm. However, after the distillation, the phenol concentration in the black liquor distillate was 348 ppm. In this way, the recovery of phenol could be determined and was about 12%.

2. Moisture content of the plywood varied between 12.6% and 14.4%. However, the data analysis of variance revealed that different mixing ratios (i.e. 1:3, 1:5, and 1:7) between the concentrated distilled black liquor and tannin crystals as well as between the concentrated distilled black liquor and phenol crystals did not bring about significant effect on the moisture content.

3. Plywood density ranged about 0.59 - 0.69 g/cm ³ . It turned out that different mixing ratios of the concentrated distilled black liquor and tannin crystals as well as between the concentrated distilled black liquor and phenol crystals significantly affected the density, whereby the higher the portion the tannin crystal or the phenol crystals the greater the density. However, at particular mixing ratio, the use of phenol crystals brought out the plywood with the density greater than using tannin crystals.

4. The bonding strength of plywood employing the glue which in its formulation included tannin crystal was about 1.64 - 6.32 kg/cm ² . Meanwhile, the strength of the corresponding plywood that used the glue incorporating phenol crystal was significantly much higher, as proved through the data analysis of variance, i.e. 18.36 - 24.96 kg/cm ² . This last figure could conform to with the Indonesian Industrial Standard for plywood's bonding strength (i.e. 14.0 kg/cm ² ).

5. Further were depicted the experiment results on plywood manufacture which was implemented using the glue formulated from the mixture (reaction) of distilled black liquor, phenol crystal, and formaldehyde. In such formulation, as described previously, the mixing ratios between phenol crystals and the distilled black liquor were varied at four levels. It turned out that the level ratio at 1:10 brought out the plywood with the most satisfactory bonding strength, i.e. 24.0 kg/cm ² , also as confirmed through the data analysis.

Figure 1. Relation between ratio of phenol to the distillate and bonding strength of the plywood, using phenol-crystals- as well as tannin-crystals-incorporating glue

Figure 2. Relation between ratio of phenol crystals to the distillate and bonding strength of the plywood, using phenol-crystal-incorporating glue

Conclusions and Suggestions

A laboratory-scale attempt on "The Possible Development of Phenol-Formaldehyde Glue Derived From the Distilled Soda's Black Liquor could wrap-up several notable and related highlights, as follows:

Recovery or the content of phenol from the original (undistilled) soda's black liquor was relatively small, i.e. 12 percent. So was the phenol concentration in the distilled black liquor, i.e. 348 ppm. In fact, such phenol was to be reacted with formaldehyde into phenol-formaldehyde (PF) compound as glue for the bonding trial of plywood.

Therefore, the distilled black liquor with low phenol content should be concentrated by adding other phenol-behaving agents. The two proposed agents were tannin crystals and phenol crystals. Afterwards, the mixture of either between the distilled black liquor and tannin crystals or between the distilled black liquor and phenol crystals was separately reacted with formaldehyde into PF compounds for the plywood bonding.

It turned out that the density and bonding strength of plywood bonded with PF that incorporated phenol crystals were greater than the one incorporated tannin crystals. Hence, PF compound with contained phenol crystal was preferred in its use as glue for plywood-bonding trial.

The results revealed that the optimum-mixing ratio between phenolic crystal additive and the distilled black liquor was 1:15 (w/w). As such, the maximum bonding strength of plywood bonded with PF glue formulated from the mixture of distilled black liquor and phenolic crystal was 24.0 kg/cm ² . This figure could comply with the Indonesian Industrial Standard for plywood's bonding strength (i.e. 14.0 kg/cm ² ).

The distilled soda's black liquor indicates encouraging prospects to be compounded with formaldehyde into PF glue for the bonding of plywood. However, such the black liquor with its low phenol content should be initially concentrated by the addition with particular amount of phenol crystal, prior to the compounding of PF to achieve satisfactory performance (qualities) of either the plywood assembly or its corresponding glue-line body itself.

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^1. R. Sudradjat and Han Roliadi (Presenters)
Research and Development Center for Forest Products
Technology (RDCFPT)
Jl. Gunung Batu, P.O.Box 182, Bogor 16001, Indonesia
Phone: 62-251-633378, Fax: 62-251-633188 and -633414
E-mail: [email protected] and [email protected]