Evaluation of staining betung bamboo (Dendrocalamus asper) using natural and synthetic dyes with and without the addition of preservatives

Bamboo is a widely utilized product. The use of dyes in coloring is now becoming important in bamboo dyeing as color can provide consumer appeal and improve aesthetics. Unlike wood, bamboo has a relatively uniform color, which is beige on the inside and green on the outside. Another important step in bamboo processing is preservation. This research examines bamboo colored using synthetic dyes using textile dyes which are azo group, natural dyes derived from the extraction of sappan wood, and examines the addition of borax boric preservatives. There are four treatments: natural dyes with preservatives, natural dyes only, synthetic dyes with preservative, and synthetic dyes only. Several tests were carried out, namely retention, penetration, staining evaluation using the CIELab method, and color change tests. It was found that natural dyes exhibited higher retention than synthetic ones, and both dyes without preservatives surpassed those with preservatives. Penetration was higher in natural dyes and those with preservatives. In comparison to the natural dyes, the color produced from synthetic dyes has a higher red intensity and a darker brightness level. While the addition of preservatives produces a lighter color with a higher brightness value. All treatments showed discoloration due to UV light exposure.


Introduction
Bamboo is one of the non-timber forest products that has wide utilization as raw materials for wood pellets, laminated bamboo, bamboo flooring, paper raw materials, and others.One of the reasons for the shift from wood to bamboo in this function is none other than because bamboo has a faster growth time, which is within 3-4 years, bamboo can already be harvested, so the availability is abundant.Another advantage of bamboo over the wood are bamboo is cheaper than wood, has long and tight fibers, flexible and does not break easily, and has a high tensile strength [1].Based on Badan Pusat Statistik (BPS) (2020), bamboo production in Indonesia is also relatively high, totaling 11,303,317.7 culms in 2020.One of the bamboos that is commonly utilized and thrives in Indonesia is Betung Bamboo (Dendrocalamus asper).This type of bamboo categorized as large bamboo which has a bottom diameter of up to 26 cm and a height of up to 25m.The physical characteristics of betung bamboo are green skin with 41-46 internodes.Betung bamboo is commonly found in clumps, in one clump with a diameter of 3.5-5m2 there are 28-41 stems [2].
Unlike wood, which has a variety of colors, bamboo generally has a similar color, which is yellowish beige on the inside and green on the outside.Therefore, coloring becomes an important aspect to diversify the color of bamboo, attract more attention, and increase its aesthetic value.The use of dyes in coloring is also able to appeal to consumers.Dyes, based on their source of acquisition are divided into two groups, namely natural dyes and synthetic dyes.Synthetic dyes are artificial dyes that are the result of chemical reactions of coal-or petroleum-based materials such as benzene, naphthalene, and anthracene.Natural dyes are dyes obtained from plant or animal extractions [3].There are several types of natural dye sources such as sappan wood which produces red color, turmeric which produces yellow color, pandan leaves which produce green color, spirulina which produces blue color, and many others.The advantages of synthetic dyes are that they are easy to obtain, have a variety of colors, and are more practical in application.However, synthetic dyes have a high hazard to the environment and human health.For this reason, natural dyes were developed that are more friendly to the environment and humans [4].The use of natural colorants in large industries is also not widely utilized, so the development of this is also important.
On the other hand, preservation is one of the processing stages in bamboo that aims to extend its lifespan.As is known, bamboo is relatively easily damaged due to the presence of biological and nonbiological destroyers, such as termites, powder beetles, weathering fungi, and coloring fungi.Therefore, it is important to carry out a preservation process to extend the service life of bamboo [5].Preservatives that can be used must be toxic to destructive organisms, permanent, permeable, safe to use, non-destructive to bamboo, widely available and inexpensive.One commonly used preservative that has been proven effective in increasing the service life of bamboo is borax boric, which consists of a mixture of borax and boric acid [6].
Until now, there has not been much research on the coloring characteristics of bamboo colored with natural and synthetic dyes.Whereas bamboo has a higher permeability than wood, bamboo also has the potential to be colored like wood [7].There is previous research on bamboo coloring by Dhamodaran (2007) using various natural dyes, one of it is sappan wood.The study compared the color of bamboo dyed with and without the addition of a mordant.As a results, sappan wood can produce a pale red color without any addition of mordant.But when K2Cr2O7 mordant is added, it can produce a dark reddish-brown color.The research only discusses the color obtained from various natural dyes, not the durability of each dye.There is also no research on coloring using synthetic dyes or the effect of adding preservatives to the color.Based on this description, this research examines bamboo colored using synthetic dyes, natural dyes, and examines the effect of using preservatives.The natural dye used in this research comes from sappan wood which contains brazilein compounds that produce a red color when the pH is neutral [8].While the synthetic dye used is Wantex dye no. 1. which is a textile dye commonly used by large industries.This research will focus on bamboo colored using natural and synthetic dyes and will combine coloring and preservation.

Bamboo strips preparation.
The Bamboo strips samples were obtained from betung bamboo from Pasanggrahan Baru Village, Sumedang Regency, West Java.Betung bamboo was cut to a size of 200±10 mm x 25±5 mm x 10±1 mm.The bamboo was then dried at 40 ℃ to an air-dried moisture content of 18-22%.18-22%.Bamboo is conditioned first before coloring (figure 1).The preparation of sappan wood extract begins with dissolving sappan wood shavings in water in a ratio of 1:30, then boiling at 90±5 ℃ for 1 hour.The solution was then filtered with a 400 mesh sieve and left for 24 hours [8].

Synthetic dyes solution making.
The making of synthetic dyes solution begins with dissolving 1 sachet (1,5 g) of wantex dye variant number 1 lombok red in 2 liters of water.Mix it until dissolved.

Preservatives addition in dyes solution.
A solution of natural and synthetic dyes was prepared.
Then added a mixture of borax and boric acid (both purity are 99%) in a ratio 1:2 with concentration 5%(w/v) into the solution.Mix it until dissolved.
First, dye solutions were prepared in the form of natural dyes, natural dyes with the addition of preservatives, synthetic dyes, and synthetic dyes with the addition of preservatives.The coloring process uses the hot-cold soaking method by boiling the bamboo in the dye solution at 90±5 ℃ for 1 hour.The coloring is continued by soaking the bamboo in the dye solution for 24 hours.The bamboo is then drained until there is no dripping liquid.This research used 5 samples for each treatment.
Testing the quality of bamboo coloring was evaluated using retention, penetration and color change parameters and discoloration tests.Retention testing is carried out by weighing before and after the sample is treated with color.Before coloring, the bamboo strips were weighed first and recorded (b1).
Immediately after coloring, the bamboo is drained until no more water drips.The bamboo was then weighed again after staining and recorded (b2).Bamboo retention was calculated using the following formula: Meanwhile, penetration testing was carried out by cutting the middle part of the bamboo on the colored sample, photographed using a Samsung A32 mobile camera, and then measured for the depth of color that can enter the bamboo using the ImageJ application.
Color change testing is done by measuring the surface of the bamboo and measurements were made before and after staining.Before coloring, the bamboo strips were first measured for L, a*, and b* values using a Minolta CR-400 Chroma Meter.After the coloring process, the bamboo strips were again measured for L, a*, and b* values using the same tool and the color change test results will be compared with the standards in table 1 [9].This research used 5 samples for each treatment, and in one Color change is calculated using the following formula: The scale of color change in dyed bamboo is listed in the following table [9]: The form of this research design is a completely randomized design with a factorial experiment that has two factors, namely the type of coloring and the presence of preservatives, with each factor having two levels.The data obtained were processed using Microsoft Excel and IBM SPSS Statistics 26 applications.The results of the data processing were then analyzed for diversity using two-way ANOVA analysis of variance.The confidence level used was 95%.

Result and Discussion
Retention is the amount of coloring material present in the bamboo after the coloring process, while penetration is one of the measurement parameters that shows how deep the coloring material can go into the bamboo.As can be seen in table 2, each type of dye has a different retention.Based on the analysis of variance, at the 95% confidence level, there is a significant difference between the retention of natural dyes and synthetic dyes, as well as between dyes with and without the addition of preservatives.Similarly, penetration was significantly different for each treatment.The highest retention was obtained in natural red dyes without preservatives with a value of 8.28 kg.m -3 , followed by natural dyes with the addition of preservatives with a value of 4.24 kg.m -3 , wantex dyes without preservatives with a value of 0.178 kg.m -3 , and finally wantex dyes with preservatives with a value of 0.123 kg.m -3 .Even with penetration, the highest value was obtained in the natural treatment with the addition of preservatives at 4.565 mm, followed by natural dyes without preservatives at 3.218 mm, synthetic dyes with the addition of preservatives at 0.198 mm, and finally synthetic dyes without preservatives at 0 mm.AB notation with different letter indicates that there is significant retention difference between dyes with the addition of preservatives and without the addition of preservatives.AB notation with different letter indicates that there is significant retention difference between dyes with the addition of preservatives and without the addition of preservatives.
Natural dyes have higher retention and penetration than synthetic dyes.This is because the natural dye concentration of 3.33% is higher than the synthetic dye concentration of 0.075%.When the concentration of the solution is higher, higher retention and penetration are obtained [10,11].This is also the reason why the penetration of colorants with preservatives is higher than without preservatives.It is possible because the addition of boron can increase the concentration of the solution so that penetration becomes higher.As for the retention, both natural dye and synthetic dye without preservative is higher than the dye without preservative.This is possible because the addition of preservatives can increase the viscosity of the dye solution so that the weight gain of the solution is

Effect of dyes type on retention and penetration
less than that of the dye without additional preservatives, thus reducing its retention.This is in line with Istriana and Priadi [12], who said that the weight gained on wood impregnated using a low viscosity solution will be higher than using a high viscosity solution.
Staining was evaluated macroscopically by observing the color before and after the staining process on the betung bamboo.The betung bamboo samples used in this study had a light beige color on the inside and a dark green color on the outside.Through this coloring process, both natural and synthetic dyes produce bamboo with a different color than the original bamboo.Bamboo stained with sappan wood's natural dye produces bamboo with a brownish red color.Sappan wood contains brazilin compounds that will produce a yellow color, and brazilein compounds that will produce a red color.The brazilin compound is very easy to oxidize due to the addition of OH and turns into a brazilein compound, for this reason, the color produced by sappan wood can be different according to the pH of the solvent used.In this study, sappan wood was extracted using water that has a pH range of 6-7, so that the resulting color is red to purplish red [8,13].So when applied to betung bamboo coloring, the bamboo will be brownish red on the inside, and very dark brown on the outside.In contrast, the inside of the bamboo applied with wantex synthetic dye has a lighter red color than the natural dye.This is because the variant used is wantex number 1 lombok red.This color is a red that resembles chili red, with a more vibrant red color.For the outside of the bamboo, visually it is not much different from bamboo colored with natural dyes, as it produces a very dark brownish color.
On the outside of the bamboo, the red color from both types of dye does not increase the reddish hue much.This is because the outer part of the bamboo has a special coating, has a fiber composition with thick walls, and contains a silica wax layer that prevents water transfer in the bamboo.This also makes it difficult for the dye to penetrate into the bamboo, so the color of the bamboo on the outside does not experience a large red color change [14,15].
Coloring with both types of dyes decreased the brightness value of the bamboo (table 4).This can be seen from the large ∆L values, which indicate that there is also a large effect from this coloring.A negative ∆L value indicates that the dyed bamboo has a darker color than the undyed bamboo.The positive and very large ∆a* values obtained for both dye types indicate that both natural and synthetic dyes can increase the reddish hue of the bamboo.Whereas the ∆b* values for both types of dyes were relatively small, indicating no significant change to the blue-yellow hue from this coloring process.Overall, as seen from the ∆L and ∆a* values, both natural and synthetic red dyes can make the bamboo color darker and redder.When compared, synthetic dyes have larger ∆L and ∆a* values than natural dyes.This indicates that synthetic dyes are more able to increase the reddish tone and decrease the brightness of the bamboo compared to natural dyes.
Coloring bamboo with the addition of preservatives produced lighter colors than bamboo colored without the addition of preservatives.In natural dyes with the addition of preservatives, the resulting bamboo had a brighter brownish-red color compared to natural dyes without preservatives.Whereas in synthetic dyes with preservatives added, the resulting bamboo has a red color that is more similar to chili, and brighter than synthetic dyes without preservatives.The preservative used is borax boric which is a salt compound that can act as a fixator, where a fixator is a compound that can lock in color.Salt fixators have Na+ ions that can bind covalently with OH-groups found in the bonds between dyes and cellulose in bamboo.Na+ ions, which are metal ions can bridge the OH-group so as to strengthen the covalent bond between the dye and bamboo, both of which have OH-groups.The greater the concentration of metal ions, the stronger the bond that occurs will be better [16].This is the reason why bamboo dyed with additional preservatives in the form of boracic salts has a lighter color.
Coloring using additional borax boric preservative on the inside of the bamboo had an effect on decreasing the ∆L value.The ∆L obtained was smaller than the value without the addition of preservative.A negative ∆L indicates that the brightness level after coloring decreased compared to before coloring.The smaller ∆L in coloring with the addition of preservatives indicates that the change in brightness is smaller than in coloring without the addition of preservatives, which also means that  the brightness in coloring with the addition of preservatives is higher.This is in line with the research of Rahmah et al. [16] which states that the provision of salt as a fixator can increase the value of L.
The ∆a* value obtained with the addition of preservatives is smaller than that obtained without the addition of preservatives.A positive ∆a* indicates that there is an increase in red color intensity.While ∆a* was greater in coloring without the addition of preservative compared to coloring with the addition of preservative.It is also seen that bamboo without the addition of preservative has a more intense red color intensity.As for ∆b* there was no significant difference between the treatment of the addition of preservatives and without the addition of preservatives.It can be concluded that the addition of borax as a fixator can increase the brightness and decrease the intensity of the red color [16].
Discoloration is a serious problem that is often faced when bamboo is stored in the open air.One of the main factors contributing to discoloration is exposure to UV light from the sun.Dyed bamboo has a high ability to absorb UV light.This is because bamboo has lignin components and chromophore components such as phenolic hydroxyl groups, aromatic skeletons, unsaturated double bonds, and carbonyl groups.When the chromophore component, which is responsible for the appearance of color, is exposed to UV light, the light will break the chemical bonds in the chromophore component and cause the formation of new aromatic compounds and free radical compounds, along with changes in the chromophore component.UV light will also break down lignin, degrading lignin, given that lignin has a high ability to absorb UV light.Applied dyes when exposed to UV light will also undergo reduction or oxidation.In short, the energy emitted by UV light can break chemical bonds in the chromophore component, degrade lignin, and change the chemical composition of the coloring material.Some of these things then cause color changes [17,18].UV light is indeed the main factor for color change, but besides that, there are other factors that can affect color change, such as humidity.Moisture affects color change because bamboo is a material that absorbs water very easily.High humidity can accelerate the dye degradation process, trigger oxidation reactions, and facilitate other reactions that can cause color changes.The presence of oxygen can also trigger the formation of free radicals that result in color changes [19,20].
In general, the change in bamboo color after exposure to sunlight is shown in figure 3. The a* value that describes the red-green color decreased over time in all treatments.The change in a* decreased dramatically when entering week 2, then appeared smaller and more stable in the following weeks.The decrease in the a* value indicates that the intensity of the red color decreases over time.This is possible due to the degradation of compounds that give rise to products containing green chromophores such as quinone and quinonemethide [21].The b* value that describes the yellow-blue color increased in the first week, then continued to decrease in the following week.This yellow-blue color change occurs due to lignin degradation.The increase in b* value in the first week occurred due to lignin degradation, which then formed carbonyl compounds such as paraquinones, which are chromophore compounds.In week 2 onwards, there was a drastic decrease in b* value, this was possible because UV light reduced paraquinones to hydroquinones [21].Changes in brightness in all treatments showed a decreasing trend, as seen from the decrease in L value.This is possible because UV light degrades lignin into quinones, resulting in darker colored bamboo [20].
As mentioned earlier, color change is also influenced by the stability of the dye component used [22].As seen in figure 4, dyes with the addition of preservatives have smaller color changes compared to dyes without the addition of preservatives.This shows that the provision of preservatives that function as fixators can make the dye more stable because preservatives in the form of salt themselves can increase the strength of the covalent bond between bamboo and dye [16].The color changes in bamboo using natural dyes without preservatives and synthetic dyes without preservatives are not significantly different.However, natural dyes with preservatives have a smaller color change than synthetic dyes with preservatives.This is because natural dyes may contain extractive substances from 3.3.Discoloration test sappan wood extracted during dye extraction.Extractive substances themselves can act as antioxidants that can protect against photooxidation [20].In addition, the synthetic dyes used, namely Wantex brand dyes, are azo group dyes which include synthetic dyes that are prone to discoloration due to UV exposure or oxidation [23].Overall, all treatments experienced a drastic color change in week 2, then became less discolored in the following weeks due to the structure of the dyed bamboo becoming stable.This also shows that photodegradation caused by UV light does not occur to the interior of the bamboo but only on the surface [22].Based on the description, the treatment that has the best resistance to UV light as the main factor of discoloration was natural dyes with the addition of preservatives.However, all treatments are not recommended for outdoor use.As for outdoor use, it is required to add a compound that can protect stained bamboo from photodegradation.

Conclusion
This study evaluated bamboo coloring using natural and synthetic dyes, with combined treatments of preservative addition and without preservative addition.It was found that retention of natural dyes was higher than synthetic dyes, while retention with the addition of preservatives was lower than without the addition of preservatives.Penetration of natural dyes was higher than synthetic dyes, while penetration of dyes with the addition of preservatives was higher than without the addition of preservatives.The color produced from synthetic dyeing has a higher red intensity and produces a darker brightness level than natural dyeing.While the addition of preservatives produces a lighter color than without the addition of preservatives, with a higher brightness value and a smaller red color intensity.The color change test showed that all treatments experienced color changes caused by the breakdown of lignin and chromophore components by UV light into other chromophore components and free radicals.Color change is also affected by the presence of oxygen and moisture.Color stability also affects color change.The best treatment obtained from this study is natural dyes with the addition of preservatives, which show the highest penetration and has better photodegradation resistance.

Figure 1 .
Figure 1.Bamboo strips sample a) Outer bamboo b) Inner bamboo (Source: Personal documentation)2.1.2.Sappan wood extraction.The preparation of sappan wood extract begins with dissolving sappan wood shavings in water in a ratio of 1:30, then boiling at 90±5 ℃ for 1 hour.The solution was then filtered with a 400 mesh sieve and left for 24 hours[8].

Figure 2 .
Figure 2. Minolta CR-400 Chroma Meter a) Calibration b) Data collection c) Data obtained (Source: Personal documentation) ∆E = Color difference ∆L = Brightness difference = L after -L before ∆a* = Red or green difference = a* after -a* before ∆b* = Difference in yellow or blue = b* after -b* before changes due to sunlight is carried out by placing bamboo in the open air.The bamboo was dried for 4 weeks in an open room exposed to sunlight and rain.Every week, the bamboo strips were measured for L, a* and b* values using a Minolta CR-400 Chroma Meter.Color change was measured using formula (2).This research used 5 samples for each treatment, and in one sample two spots were measured, on the inner and outer of bamboo strips.

Figure 3 .
Figure 3. a) Color change b) Brightness change c) Red-green discoloration and d) Yellow-blue discoloration