Decreasing the melting point? Replacing benzyl chloride with a lignin-degradation product in cellulose etherification.

doi:10.21203/rs.3.rs-1616025/v1

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Decreasing the melting point? Replacing benzyl chloride with a lignin-degradation product in cellulose etherification.

https://doi.org/10.21203/rs.3.rs-1616025/v1

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A cellulose ether that is easier to melt than benzyl cellulose was produced from veratryl alcohol. We successfully synthesised both veratryl chloride and bromide from the alcohol and used these two chemicals to react with Avicel® cellulose to form the novel cellulose ether veratryl cellulose (VC). Spectroscopic characterisation techniques (¹H NMR, FTIR) indicate the successful conversion of Avicel® cellulose to the cellulose ether VC, by both routes, at a degree of substitution of 1.4–1.6. Melting measurements of the VC samples show a gradual softening from approximately 110°C and that the VC is melted at below 200°C. XRD analysis confirms that the chemical treatments affect the degree of crystallinity. Size exclusion chromatography (SEC) results show that the products differ significantly in molecular weight. It seems like the VC synthesised with veratryl chloride degrades almost twice as much as if veratryl bromide is used. The cellulose ethers were soluble in DMSO, DMAc and CHCl₃.

Veratryl cellulose

melting measurements

Cellulose ether

Degree of substitution

Characterisation techniques

Size exclusion chromatography

Although cellulose is a very strong and valuable polymer, it has several drawbacks. It is, e.g., difficult to dissolve and cannot be melted (Yang et al. 2014; Acharya et al. 2021; Lindman et al. 2010). A commonly used strategy to circumvent these problems is to modify the chemical structure of the cellulose chemically, and the products of such chemical modifications are collectively called cellulose derivatives (Mali and Sherje 2022; Zhang et al. 2019; Oprea and Voicu 2020; Liu et al. 2021).

We can divide cellulose derivatives into two different groups; cellulose esters (e.g. cellulose acetate) and cellulose ethers (e.g. carboxymethyl cellulose) (Candido and Gonçalves 2016). Of these, cellulose ethers are dominating the market, with US$ 11.3 billion in 2021 to $ 14.62 billion in 2016 (Kukoyi 2016). Commercial cellulose ethers are often used as thickening, stabilising, water-retaining and dispersing agents in, e.g., the building industry (Carraher and Charles 2003; Berglund et al. 2009).

The change towards renewable recourses is imminent. However, cellulose etherification is today made with fossil-based chemicals, e.g. chloroacetic acid and ethyl chloride from fossil sources. For example, the historically important benzyl cellulose (BC) is produced by the etherification of cellulose with petroleum-based benzyl chloride. This cellulose ether was commercially manufactured before World War II, and is one of few cellulose derivaties that can display a melting point (Braun and Meuret 1989; Ramos et al. 2005). BC is still of interest since it can be used in haemodialysis membranes (Sundman et al. 2015). The production of this polymer is, however, not done commercially today. Nevertheless, if the fossil-based benzyl chloride (Fig. 1a) could be replaced with a renewable chemical, a fossil-free polymer with similar properties can be produced. Also, if an even more bulky substituent is used, we hypothesise that the formed cellulose derivative can show even more moldable properties than BC.

A structurally related, but bulkier, chemical is Veratryl alcohol (3,4-dimethoxybenzyl alcohol) (Fig. 1b). Veratryl alcohol is a bio-based chemical naturally synthesised from the degradation of lignin. Discovered in 1961 (Russell et al. 1961), the biological origin of this lignin-degradation product was established in 1978 (Lundquist and Kirk 1978). In our chemical transformation use quite strong and toxic chemicals (SOCl₂ and PBr₃), but this is only an initial laboratory study.

As shown in Fig. 1, the difference between benzyl chloride, on the one hand, and veratryl chloride, on the other hand, is that the latter has two electron-withdrawing methoxy groups. These groups make the veratryl molecules less reactive. However, these groups also make the veratryl bulkier than the respective benzyl group. Thus a lower melting point can be expected for any veratryl cellulose ether than for the respective benzyl. This paper thus intends to first convert Veratryl alcohol to both Veratryl chloride and bromide using chemical synthesis. Then we test these products concerning their reactivity towards cellulose. We also studied the produced veratryl cellulose (VC) with several chemical analyses. According to these principles, a partly bio-based cellulose ether can be synthesised via this route but the veratryl chloride/bromide is probably less reactive than the respective benzyl. The hypothesis is that a cellulose ether that is more easily melted than benzyl cellulose should be formed. The concept presented herein will help develop and synthesise new bio-based cellulose derivatives. Based on the research outcomes, decisions can be made to apply this strategy with similar degradation products to further explore the production of different bio-based materials as well as develop cellulose-ether-based bioplastics.

Materials

Avicel®PH-101 microcrystalline cellulose (∼50 µm size, Sigma Aldrich), dimethyl sulfoxide- (DMSO, Sigma Aldrich), trimethylamine (Et₃N, Sigma Aldrich), Acetic acid (Sigma Aldich), chloroform (CHCl₃, VWR Chemicals), dichloromethane (CH₂Cl₂, VWR Chemicals), phosphorus tribromide (PBr₃, Sigma Aldrich), thionyl chloride (SOCl₂, sigma Aldrich), Veratryl alcohol (VOH, sigma Aldrich), acetone (Sigma Aldrich), benzyl chloride (Sigma Aldrich), chloroform-D (CDCl₃, Armar Chemicals, 99.8 atom%D), dimethyl sulfoxide-d6 (DMSO-d6, Armar Chemicals, 99.8 atom%D), dimethylacetamide (DMAc, VWR Chemicals), 4- dimethylamino pyridine (DMAP, Reagent Plus® ≥99, Sigma Aldrich), methanol (MeOH, VWR Chemicals), propionic anhydride (Sigma Aldrich), 2-propanol (VWR Chemicals), pyridine (Sigma Aldrich), tetrabutylammonium fluoride (TBAF·3H₂O, Sigma Aldrich), sodium bicarbonate (NaHCO₃, VWR Chemicals), anhydrous sodium sulfate (Na₂SO₄, VWR Chemicals), sodium chloride (NaCl, VWR Chemicals) were all used as received. NaOH (VWR Chemicals) was pulverised and used immediately. All the mentioned chemicals were pure (≥ 98%) and used without further purification.

Methods

Synthesis of Veratryl chloride

Following the general procedure in literature (Guan et al. 2019; Miyamura et al. 2013): To 1.157 mL of (Et3N) 0.60 mL of (SOCl₂) was added in an ice bath, the obtained viscous yellow solution was diluted with 10 mL of dry CH₂Cl₂. The resulting solution was added dropwise to 1.00 mL Veratryl alcohol solution in 10 mL of dry CH₂Cl₂. The reaction mixture was allowed to equalise overnight, after which the reaction appeared complete. The reaction mixture was quenched with 10 mL of ice water, stirred for 30 min., and then filtered. The filtrate was dried over anhydrous Na₂SO₄ and then concentrated by rotary evaporation yielding the final product veratryl chloride (3,4-dimethoxybenzyl chloride).

Synthesis of Veratryl bromide

Following the general procedure in literature (Wu and Huang 2014): veratryl alcohol (9.92 g) was dissolved in 25 mL of CH₂Cl₂, and the solution was cooled to 0°C. Then, a PBr₃ (1.0 M) solution in CH₂Cl₂ (25 mL) was added via syringe slowly to the alcohol solution. The obtained yellow mixture was stirred at room temperature for another four h. The reaction was carefully quenched with ice water (100 mL) and extracted with CH₂Cl₂ (3 x 50 mL). The combined organic layers were successively washed with saturated NaHCO₃ (100 mL), distilled water (100 mL), and brine solution (NaCl solution, 100 mL) and dried over anhydrous Na₂SO₄. Finally, the solution was concentrated in a rotary evaporator to afford the desired Veratryl bromide (3,4-dimethoxybenzyl bromide).

Synthesis of Benzyl Cellulose (BC) and Veratryl Cellulose (VC)

The synthesis method was based on the procedure reported in the literature (Sundman et al. 2015; Ramos et al. 2005): Briefly: 2.82 g (TBAF.3H₂O) salt was mixed with 15 mL DMSO until fully dissolved. 0.45 g Avicel®PH-101 cellulose was added to the mixture with intense stirring at room temperature (for 30 min) then at 60°C (for one h) until the solution mixture was clear. A solution of (0.37g pulverised NaOH in 5 ml DMSO) was added to the mixture with vigorous stirring. 1 mL Benzyl chloride was added to the solution with subsequent stirring for four h at a constant temperature (70°C ). The produced benzyl cellulose suspension was precipitated into (1:4 H₂O: MeOH) solution and was then neutralised with dilute acetic acid. The benzyl cellulose polymer was obtained by filtration, washing with excess (1:4 H₂O: MeOH) solution, and drying for 48 h under vacuum pressure at 50°C. The two Veratryl cellulose polymers were synthesised following the same method for synthesising benzyl cellulose by replacing the benzyl chloride with Veratryl chloride or Veratryl bromide, keeping the same molar ratio (1:3) between Avicel cellulose and halide.

Perpropionylation of Avicel® cellulose and cellulose derivatives

Following the synthesis method reported by Sundman et al. (2015), a mixture of 0.3 g Avicel® cellulose, 5 ml pyridine, 5 ml propionic anhydride, and 0.2 g DMAP as a catalyst was heated and kept isothermal at 80°C for > 24 h. Then the reaction mixture was cooled to room temperature and precipitated in 200 ml 2-propanol. The obtained polymer was filtered off, washed with 2-propanol and dried at 70°C for one week under reduced pressure. The same procedure was used for the Perpropionylation of cellulose derivatives by replacing the Avicel cellulose with other cellulose derivatives (Benzyl and Veratryl cellulose).

Solubility measurements

The solubility of the cellulose derivatives was checked by dissolving 10 mg of dry solid materials in 1 mL solvent in glass test tubes with caps. The suspensions were then put in an ultrasonic bath for 30 min, and the samples were visibly swollen. The samples rested at room temperature for a few hours and then again in the ultrasonic bath for 30 minutes. The solubility of the samples was determined visually after resting at room temperature overnight.

Melting measurements.

If necessary, the cellulose ether was ground to a powder. A few grains of the sample were then transferred to a capillary tube for measurement. The capillaries were put in XXXXXXX. The samples were heated to 80°C. The temperature was then gently increased until the material visibly softened., and the temperature was recorded. The temperature was then continuously increased to 230°C with continuous softening, and final blackening, of the material.

Characterisation techniques

Nuclear Magnetic Resonances (¹H-NMR) spectroscopy was performed to determine the chemical structure of cellulosic derivatives and recorded using an Avance Bruker DPX (400 MHz). The samples were dissolved in deuterated chloroform solvent, and its ¹H-NMR singlet was used as an internal reference (CDCl₃, ¹H 7.25 ppm).

A Bruker Vertex 80v Fourier Transformed Infrared spectrometer with Attenuated Total Reflectance mode (FTIR-ATR) was used with a detector (deuterated triglycine sulfate-DTGS) was used to analyse the samples with FTIR. The FTIR spectra range (400–4000 cm^− 1) were recorded with 128 scans per sample and a resolution of 4 cm^− 1.

A Size Exclusion Chromatography (SEC) instrument coupled to a Refractive Index and a Light Scattering (LS) detector was used to analyse the molecular weight distribution of the perpropionylated cellulosic derivatives. These cellulose derivatives were dissolved in chloroform for measurements at a 5 mg/mL concentration. The SEC system consisted of a high-pressure pump (Hewlett Packard-series 1100), a guard column, two serial T6000M columns, and a 0.45 µm PTFE filter in series. The auto-sampler, columns, and detector temperature were set at 35°C, the eluent used was chloroform, and the flow rate was 1 ml min^− 1. The detector system was a Malvern Omnisec Reveal containing a refractive index (IR) and a multi-angle light scattering (MALS) detector. The detector response was calibrated using two polystyrene standards (one broad and one narrow). The data were evaluated with the Omnisec V11 software from Malvern using the Debye model applying a first-degree polynomial.

X-ray diffractograms (XRD) were obtained using a PANalytical Xpert3 Powder X-ray diffractometer (XRD) with operating system Cu Kα (1.54 Å) radiation at 25 mA and 40 kV. The measurements were recorded from 5^o to 45^o (2θ) at a scan speed of 8 s per point.

Solubility test

Table 1 summarises the solubility tests for cellulosic derivatives and their perpropionylated counterparts in water and several organic solvents at 25 ^oC and a concentration of 10 mg/mL. The insolubility of cellulose in common solvents is well-known, and we will not discuss it here. The non-perpropionylated cellulose derivatives (BC, VC1 and VC2) are not soluble in hydrogen bonding solvents (water, MeOH and acetone) but solubilise in the less polar solvents (CHCl₃, DMSO and DMAc). A higher solubility-to-DS ratio BC is thus seen than in previous studies (Sundman et al. 2015), and the VCs show similar solubilities. In the case of perpropionylated cellulose derivatives (P-cellulose, P-BC, P-VC1 and P-VC2), these polymers are not soluble in the protic solvents (water and MeOH) but solubilise in all the other solvents tested (acetone, chloroform, DMSO, and DMAc). The reason for this drastic change of solubility for the cellulosic derivatives due to the perpropionylation is probably a break-up of the remaining structure, and in the case of Avicel® cellulose, a total disruption if it. We utilise this phenomenon since we then solubilise both P-Cellulose and the corresponding cellulose derivatives for SEC analysis.

Table 1

Solubility of the cellulose derivatives in different solvents at a concentration of 10 mg/mL. "i" represents insoluble while "s" represents soluble.
Sample Solvent	BC	VC1	VC2	P-Cellulose	P-BC	P-VC1	P-VC2
H₂O	i	i	i	i	i	i	i
MeOH	i	i	i	i	i	i	i
(CH₃)₂O	i	i	i	s	s	s	s
CHCl₃	s	s	s	s	s	s	s
DMAc	s	s	s	s	s	s	s
DMSO	s	s	s	s	s	s	s

Melting measurements.

The melting of the BC and the VCs was gradual, and no exact melting point can, unfortunately, be reported. In Table 2, the temperature where visible softening (FST) of the material could be seen and the temperature where we saw a significant change was observed is reported. It must be stated, however, that the slow and gradual change in structure (softening/melting) can be challenging to observe and that the numbers are based on what we saw.

Table 2

The first softening (FST) and the significant softening temperature (SST) of the cellulose ethers. Average of three to four measurements (standard deviation).
Name	FST, (°C)	SST, (°C)
BC	107 (3)	137 (6)
VC1	111 (18)	135 (5)
VC2	104 (2)	118 (3)

The only significant change is the SST between BC and VC2. However, the softening of these cellulose ethers is gradual, and the melting points also depend on impurities in the samples. Interesting, however, is that at even higher temperatures, the VC seem to melt. At approximately 170–200°C both the VCs begin to show a whitish or light brown melt. The BC, however, did not show any melt at all, it degrades to a blackish char-like, substance. This, we expected from the literature (Isogai et al. 1984). These authors showed that the melting of BCs depends on both DS and MW and concluded that the DS needed to be close to 3 while the DP needed to be < 140 if a clear melting point for BC should appear. We do not see this for the VCs studied herein. In the supplementary data we show this phenomenon in a film (Supplementary_matials_ Melting_Film.mp4), where the heating is speed-up 32 times. The sample in the middle (to the left) is BC and the sample to the right s VC2. Unfortunately, the film's resolution is too low to show the FST and SST. However, the presence of air bubbles in the samples complicates the interpretation of what is seen in the film, and it would be beneficial to perform both the synthesis and the melting measurements in another environment (vacuum? inert atmosphere?) to avoid both bubble formation, and air catalysed degradation.

Fourier Transformed Infrared (FTIR) measurement.

In Fig. 2, we present the FTIR spectra for the analysed cellulose-based polymers (Avicel® cellulose, BC, VC1, and VC2). The figure shows that there are absorption bands at (2850 cm^− 1) and (1100 cm^− 1), which are associated with C-H aliphatic stretching and bending modes, respectively. In the case of the cellulose spectrum, the absorption band at (3300–3500 cm^− 1) is associated with OH groups (-OH stretching). This absorption band is diminished and shifted in the spectra for the cellulose ethers (BC, VC1 and VC2). Furthermore, Fig. 2 also shows that the absorption band associated with the aromatic rings (C=C stretching mode) appears around (1450–1500 cm^− 1) for BC and at (1500–1600 cm^− 1) for the VCs, and this increase in wavenumber indicate an increased charge density caused by the donating methoxy groups. In the same way, the absorption band associated with aromatic sp2 (C-H bending mode) is shifted and appears around (650–750 cm^− 1) for BC and around (750–850 cm^− 1) for the VCs. Lastly, an absorption band at (1300 − 1250 cm^− 1), related to the (C–O stretching mode) appears solely in the VCs due to the methoxy groups in the veratryl structure. In short, the FTIR measurements indicate the successful modification and replacement of OH groups in Avicel® cellulose with benzyl and veratryl structure via the benzylation and veratrylation reactions, respectively. Also, the shift in peaks between BC and VCs indicates donating methoxy groups (O-CH₃) within the VC structure (Young et al. 1951).

Proton Nuclear Magnetic Resonance (¹H NMR).measurements

The cellulose ether's degrees of substitutions (DSs) were calculated as DS_NMR of perpropionylated derivatives in line with the work reported in the literature (Ramos et al. 2005; Li et al. 2011; Sundman et al. 2015). DS_NMR was estimated according to Eq. 1 (for P-BC) and Eq. 2 (for P-VC1 and P-VC2):

$$DS=\frac{7}{5} x \frac{A1}{(A2-\frac{2}{5}A1)}$$

$$DS=\frac{7}{3} x \frac{A1}{(A2-\frac{8}{3}A1)}$$

In equations (1) and (2), A1 represents the integral in the ¹H NMR spectra for the aromatic peak (δ ≈ 7.2 ppm for P-BC and δ ≈ 6.7 for P-VC1,2), while A2 represents the integration for the aliphatic peaks (the integral of the area 3.0 ≤ δ ≥ 5.5) (Ramos et al. 2005; Li et al. 2011; Sundman et al. 2015). The reasoning behind equations 1 and 2 is found in the supplementary materials Fig S1, S2, and table S1.

The resulting DS_NRM, calculated using Equations 1 and 2, are presented in Table 3.

Table 3

The DS_NMR of the cellulose (derivatives).
Name	DS_NMR
BC	1.2
VC1	1.6
VC2	1.4

Figure 3a. displays (from bottom to top) the ¹H NMR spectra of the benzyl chloride (B-Cl), veratryl alcohol - (V-OH), veratryl chloride (V-Cl), and veratryl bromide (V-Br), respectively. The ¹H NMR spectrum (400 MHz, internal standard CDCl₃) for (B-Cl) shows the two expected signals for benzyl chloride (B-Cl) that appears at (7.50 ppm, m, 5H) and (4.46 ppm, s, 2H). The ¹H NMR spectrum (400 MHz, internal standard DMSO-d6) for veratryl alcohol shows, on the one hand, the five expected peaks appears for veratryl alcohol (V-OH) at (6.90 ppm, m, 2H), (6.80 ppm, d, 1H), (5.25 ppm, t, 1H), (4.50–4.46 ppm, s, 2H), and (3.85–3.70 ppm, s, 6H). On the other hand, the spectra for veratryl chloride (V-Cl) and veratryl bromide (V-Br) show all the previously mentioned peaks for (V-OH) except the peak associated with the hydroxyl group. Thus, the ¹H NMR analysis indicates the successful synthesis of veratryl chloride or veratryl bromide, respectively, from veratryl alcohol.

We illustrate the ¹H NMR spectra (400 MHz, internal standard CDCl₃) of the per-propionylated cellulose derivatives [P-cellulose, P-benzyl cellulose (P-BC), and P-veratryl cellulose (P-VC1 and P-VC2)] in Fig. 3b. As described in the literature, the signals for the per-propionylated Avicel® between 3 and 5 ppm are associated with cellulose backbone structure: (H3) 5.10 ppm, (H2) 4.81 ppm, (H1) 4.41 ppm, (H6) 4.06 ppm, (H4) 3.71 ppm, and (H5) 3.53 ppm (Ramos et al. 2005; Li et al. 2011; Kono et al. 2016a). The signals between (0.80–2.5) ppm correspond to the methyl and methylene groups of the propionic acid ester (H7 and H8). In the P-benzyl cellulose (BC) spectrum, it is apparent that additional signals appear around 7.21 ppm (H9) and 4.65 ppm (H10), which are associated with the benzyl groups (aromatic carbon and methylene groups, respectively). In the P-veratryl cellulose derivatives (P-VC1 and P-VC2), the corresponding peaks are shifted to around 6.65 ppm (H11), 4.40 ppm (H12), respectively. Also, here, the reason for the shift between BC and VC structures in the ¹H NMR signals is the presence of electron-donating groups (methoxy groups (O-CH₃)) within the veratryl cellulose structures. This leads to enhanced negative charge density, which causes increased shielding and thus decreased chemical shifting of the ¹H NMR signals (Spiesecke and Schneider 1961; Miyamoto and Hada 2021; Kono et al. 2016b).

Furthermore, it can be observed that an additional peak, at 3.55 ppm, appear that represents the methoxy group in the veratryl substituents (H13). The ¹H NMR spectra thus show that we have successfully synthesised and characterised this novel cellulose ether. Overlapping of the cellulose backbone ¹H NMR peaks was seen for benzyl cellulose and depended on DS_NMR (Ramos et al. 2005; Li et al. 2011). In our data, this phenomenon was also evident for also the veratryl cellulose samples. Additionally, as reflected in Table 3, the equal amount of reagent gives higher DS_NMR if veratryl chloride (1.6) or bromide (1.4) is used than if benzyl chloride (1.2) is used. However, there is competition between etherification and hydroxide catalysed hydrolysis; hydrolysis might explain the impression of a reversed order of reactivity since it is known to be a quick reaction. However, this is hypothetical. The molecular weight of the polymers has to be considered to show upon any significant hydrolysis.

X-ray diffraction (XRD) measurements

Figure 4. displays the X-ray diffractograms obtained for cellulosic derivatives (Avicel® cellulose, BC, VC1, and VC2). The WAXD patterns of Avicel® cellulose show that there are characteristic diffraction peaks at 2θ = 34.6^o, 22.5^o and 16.5^o, which correspond to the planes (004), (200) and (110), in Cellulose-I crystals, respectively. The overall XRD patterns with corresponding peaks are in good agreement with the literature (Li et al. 2011; Thakur et al. 2020; Ramos et al. 2005; Ass et al. 2006; Ju et al. 2015) and confirmed the presence of cellulose-I. After derivatisation (benzylation and veratrylation, respectively), the characteristic peaks of cellulose-I disappeared, and a new peak at 2θ = 38.9^o and Å= 2.31 was observed, which is generated from the presence of phenyl groups within the chemical structures of benzyl and veratryl units. Also, another peak was observed at 2θ = 20.2^o and Å= 4.26 for benzyl cellulose (BC). This peak shifted slightly to 2θ = 20.5 ^o and Å= 3.82 for veratryl cellulose (i.e. VC1 and VC2), and this shift is due to the presence of methoxy groups (withdrawing groups) within the veratryl units in compression with benzyl units. Furthermore, as the degree of crystallisation of cellulosic materials is affected by chemical treatments (Wu et al. 2020), the disappearance of crystallinity during the derivatisation process is expected.

Molecular weight estimations (Size Exclusion Chromatography)

The SEC analysis was done in chloroform on perpropionylated samples, which all have a different molecular weight than the original cellulose (ether). Thus the molecular weight averages (MW averages: M_w and M_n) has to be calculated with this in mind. Although caution with the SEC of cellulose derivatives as an indication for cellulose molecular weight distribution is advised in the literature (Henniges et al. 2014; Potthast et al. 2015; Ono and Isogai 2021; Melander and Vuorinen 2001; Li et al. 2016), the potential loss of low-MW fractions was not critical. Furthermore, since we only analysed the relative decomposition, this was not an issue. Table 4 displays the MW averages for the original (Avicel®) cellulose and cellulose derivatives (BC, VC1 and VC2), both as data from the SEC measurements and as corrected, calculated values. Details of how these transformations and calculations are done are found in supporting material, but basically, we used Eq. (3)

$${M}_{\text{w, corrected}}={M}_{\text{w, SEC}}*\frac{{M}_{\text{AGU,non-per-propionylated}}}{{M}_{\text{AGU,per-propionylated} }}$$

In Eq. (3) M_{w, corrected} represent the corrected, calculated M_w of the polymer in question. M_{w, SEC} represents the M_w from the SEC measurement. M_{AGU,non−per−propionylated} and M_{AGU, per−propionylated} represent the molecular weight of the AGU of the polymer prior and after per-propionylation, respectively. This calculation always assumes that DS_{BC or VC} + DS_{per−propionylation} is 3, which is a simplification, of course. However, any error brought by this simplification is small.

Table 4

The molecular weight of the AGU, the measured and calculated molecular weight averages and the degree of polymerisation (DP) for the cellulose (derivatives).
	M (AGU) (g/mol)	M_w (SEC) (g/mol)	M_n (SEC) (g/mol)	M_w (corrected) (g/mol)	M_n (corrected) (g/mol)	DP_w	DP_n
Avicel® Cellulose	162	80000	46000	40000	22000	243	138
BC	270	56000	37000	41000	27000	150	100
VC1	528	35000	26000	29000	22000	73	55
VC2	488	79000	61000	63000	49000	171	133

The M of the AGU of a cellulose derivative depends on both the DS of the AGU and the MW of the substituent. The MW averages of the polymer also depend on the DP. On the one hand, for VC1, we measured a higher DS for this polymer than both BC and VC2. The M of the AGU is also the highest. Nevertheless, the polymer has the lowest MW averages because of the much lower DP (cf. Table 4). VC2, on the other hand, show much less degradation. The data thus indicate more severe degradation during the synthesis of VC1 than VC2. Also, the data indicate almost the same degradation for VC2 as for BC produced with the same amount of reagent and NaOH. The apparent degradation supports the hypothesis from 3.3 that the competition with alkaline hydrolysis is responsible for the impression of a reversed order of reactivity towards cellulose. If hydroxide ions are consumed in the hydrolysis reaction, fewer hydroxide ions can depolymerise the cellulose, which is known to happen at these temperatures (Reyes et al. 2016). Hydrolysis is not so fast for the less reactive V-Cl, and the opposite would be true. A low polymer DP would follow, and a significant amount of hydroxide ions are consumed in the hydrolysis of cellulose. The concentration of V-Cl acting on the cellulose would thus be higher than for the other synthesises, explaining the DS_NMR. Therefore, we can say that the reactivity toward Na-cellulose seems to be in the same range for veratryl bromide and benzyl chloride and lower for veratryl chloride. However, these explanations are not backed by statistics. More experiments are necessary to make them finite.

Both veratryl chloride and bromide could be formed from the alcohol using organic chemistry. Using a typical etherification technique, the two chemicals reacted with cellulose and formed cellulose derivatives with slightly higher DS (1.4–1.6) than benzyl chloride (1.2). The spectroscopic characterisation techniques (¹H NMR and FTIR) indicated the successful conversion of Avicel® cellulose to form this cellulose ether. Excellent solubility was seen at this DS. This cellulose derivative seems easier to melt than benzyl cellulose, thus probably confirming our primary hypothesis. However, we cannot based on the presented data, establish that completely. Veratryl cellulose could be produced, a proof of concept. However, the degradation of the cellulose ethers varied and seemed to be higher when veratryl chloride was used. I.e. the degradation was much more severe when V-Cl was used as a reactant than for both V-Br and B-Cl. This was most probably the result of more negligible hydrolysis and thus more free OH⁻- ions that can depolymerise the cellulose (derivative). This indicated that hydrolysis and derivatisation are reversely co-dependent. However, the reactivity of the chemicals could only be understood with both the DS values and the MW averages in mind. From this, the apparent reactivity of the veratryl bromide seemed to be in the same range as benzyl chloride, while the reactivity of veratryl chloride appeared to be much lower.

Funding

The Kempe Foundations (Sweden) and Bio4Energy, a Strategic Research Environment appointed by the Swedish government, are both acknowledged for supporting this work.

Competing interests

The authors have no relevant financial or non-financial interests to disclose.

Author Contributions

Mohamed Yahia: Investigation, data analysis, writing – original draft.

Ola Sundman: Conceptualisation, supervision, investigation, writing, review, editing and writing of the final version.

Both authors read and approved the final manuscript.

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Decreasing the melting point? Replacing benzyl chloride with a lignin-degradation product in cellulose etherification.

Status:

Version 1

Abstract

Figures

Introduction

Materials And Methods

Materials

Methods

Synthesis of Veratryl chloride

Synthesis of Veratryl bromide

Synthesis of Benzyl Cellulose (BC) and Veratryl Cellulose (VC)

Perpropionylation of Avicel® cellulose and cellulose derivatives

Solubility measurements

Characterisation techniques

Results And Discussion

Solubility test

Proton Nuclear Magnetic Resonance (¹H NMR).measurements

X-ray diffraction (XRD) measurements

Molecular weight estimations (Size Exclusion Chromatography)

Conclusion

Declarations

References

Supplementary Files

Status:

Version 1

Decreasing the melting point? Replacing benzyl chloride with a lignin-degradation product in cellulose etherification.

Status:

Version 1

Abstract

Figures

Introduction

Materials And Methods

Materials

Methods

Synthesis of Veratryl chloride

Synthesis of Veratryl bromide

Synthesis of Benzyl Cellulose (BC) and Veratryl Cellulose (VC)

Perpropionylation of Avicel® cellulose and cellulose derivatives

Solubility measurements

Characterisation techniques

Results And Discussion

Solubility test

Proton Nuclear Magnetic Resonance (1H NMR).measurements

X-ray diffraction (XRD) measurements

Molecular weight estimations (Size Exclusion Chromatography)

Conclusion

Declarations

References

Supplementary Files

Status:

Version 1

Proton Nuclear Magnetic Resonance (¹H NMR).measurements