materials Article
Study of Almond Shell Characteristics Xuemin Li, Yinan Liu, Jianxiu Hao and Weihong Wang * Key Laboratory of Bio-based Material Science & Technology (Education Ministry), Northeast Forestry University, Harbin 150040, China;
[email protected] (X.L.);
[email protected] (Y.L.);
[email protected] (J.H.) * Correspondence:
[email protected] Received: 17 August 2018; Accepted: 12 September 2018; Published: 19 September 2018
Abstract: A large amount of almond shells are disposed of every year. The anatomical and chemical characteristics of almond shells are investigated in this paper in order to contribute to better utilization of these shells. The micromorphology, surface elements, thermal stability, crystallization, chemical composition, and relative properties of almond shells are analyzed. Under observation by microscope and electron microscope, the diameter of almond shells is 300–500 µm for large holes, and 40–60 µm for small holes present in the shell. X-ray photoelectron spectroscopy shows the elements of almond shells include C (72.27%), O (22.88%), N (3.87%), and Si (0.87%). The main chemical constituents of cellulose, hemicellulose and lignin in almond shells account for 38.48%, 28.82% and 29.54%, respectively. The alkaline extract content of almond shells is 14.03%, and benzene alcohol extraction is 8.00%. The benzene alcohol extractives of almond shells mainly contain 17 types of organic compound, including benzene ring, ethylene, carbon three bond, and other mufti-functional groups. Thermal stability analysis shows almond shells mainly lose weight at 260 ◦ C and 335 ◦ C. These characteristics indicate that almond shells have the capacity to be used in composites and absorption materials. Keywords: almond shells; anatomical structure; chemical composition; thermal stability
1. Introduction Biomass nutshell is a large yield crop residue which is generally discarded or incinerated. This not only pollutes the environment, but also wastes a large amount of resources. In order to avoid this, many scholars have undertaken research into its potential uses, including the use of biomass nut shells to produce activated carbon. Ahmad et al. used peanut shell adsorption of trichloroethylene for cleaning water [1], while Lan et al. prepared activated carbon from Hawaii nut shells [2]. Martínew et al. prepared activated carbon from walnut shells, and studied its properties [3], and Yang et al. formulated high specific surface area activated carbon from coconut shells by microwave heating [4]. Okutucu et al. produced fungicidal oil and activated carbon from pistachio shells [5]. In addition to the manufacturing of activated carbon, biomass nut shells have a number of other uses. Wongcharee et al. used macadamia nut shell residue as magnetic nanosorbents [6], and Pino et al. studied the biosorption of cadmium using coconut shells [7]. Notably, biomass nut shell has also been used in composites. Alsaadi et al. studied the effect of the content of particles on the mechanical properties of polymer composites [8], and Bae et al. have prepared composite by macadamia nut shell for capturing CO2 [9]. Bledzki et al. studied the effects of fiber physics and chemistry on the properties of composites prepared from barley shell and coconut shell reinforced polypropylene [10], and Ayrilmis et al. manufactured chestnut shell reinforced polypropylene composite [11]. In addition, Kasiraman et al. used cashew nut shells as fuel for camphor oil blending [12], and Bartocci et al. proved that biomass shells improve soil health and fertility when used as oil amendment [13]. Wang et al. demonstrated that biocarbon could possibly replace fossil fuel, and help reduce greenhouse gas emissions [14]. Materials 2018, 11, 1782; doi:10.3390/ma11091782
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Almonds are a type of biomass nut shell and are widely grown in many regions of the world including India, Pakistan, Iran, and China. As of 2014, global output of almonds was three million tons annually (data). Almond shells account for around 35–75% of the total fruit weight, so about 10.5–22.5 million tons of shells were left [15]. This huge quantity of shells has great economic and practical potential, and investigation into the best way to utilize the shell is attracting increasing attention. Rodríguez-Reinoso et al. and Toles et al. prepared activated carbon with almond shells, studying its physical, chemical and adsorptive properties, as well as estimated cost of production [16,17]. Senturk et al. have used almond shells as adsorbents to remove dye rhodamine from aqueous solutions [18]. Mohan et al. prepared magnetic and activated carbon by almond shells to remove 2,4,6-trinitrophenol from water [19], and Essabir et al. reinforced polypropylene with almond shells by extrusion process [20]. Lashgari et al. studied the effect of the loading amount of nano-clay and content of almond shell powder on the strength and properties of polypropylene composites [21]. Due to such studies into almond shell utilization, there is limited knowledge of almond shell structure and chemical properties. Caballero et al. studied the kinetics of slowing the thermal decomposition of almond shells, and analyzed the pyrolysis of lignin and whole cellulose [22]. In the studies of Essabir et al. and Elleuch et al., it is shown that almond shells are absorbent and environmentally friendly [20,23]. This article focuses on the basic chemical composition and physical structure of almond shells in order to make better use of this large quantity bio-resource. 2. Materials and Methods 2.1. Materials The almond shells used in this study were purchased from Anhui Liang Zhong Liang Food (Huai’an, China). Poplar wood particles, as a control, were purchased from Jinan Yuanfang Wood Trading Company (Jinan, China). Both almond shells and poplar particles were screened into 40–60 mesh and 60–80 mesh. 2.2. Chemical Composition The main chemical composition of almond shell particles of 40–60 mesh were measured according to Chinese standard GBT 35816-2018 (Standard Method for Determination of Structural Carbohydrates and Lignin in Biomass Raw Material). The content sum of hemicellulose and cellulose was determined by using glacial acetic acid and sodium hypochlorite as a solvent. After repeated washing, the polysaccharide in the almond shells was dissolved, then dried and measured. The content of cellulose was determined by using nitric acid and ethanol as solvent. Other non-cellulosic materials including lignin, hemicellulose, and other materials in the sample are eluted to obtain cellulose. The lignin content was determined by sulfate method. After the sulfuric acid solvent was removed, the residue was measured to determine the quality of lignin. Particles of 40–60 mesh almond shell were used to measure extractives according to GBT 35818-2018 (Standard Method for Analysis of Forestry Biomass-Determination of Extractives Content). Extractive content of almond shell was measured after the shells were treated with cold water for 48 h, hot water for 6 h, 1% NaOH for 1 h, or benzene alcohol (V benzene/V ethanol = 2:1) for 6 h. In addition, the benzene alcohol extractive solution was diluted to 0.1 mg/mL (V benzene/V ethanol = 2:1), and its chemical composition was measured by GC/MS (7890A-7000B, American Agilent Corporation, Santa Clara, CA, USA). 2.3. Infrared Spectrum Almond shells and poplar particles were scanned by Fourier infrared spectrometer (Nicolette 6700, American Water Corporation, Los Angeles, CA, USA). The KBr disk method was employed for the sample, and wavelength was 500–3500 cm−1 at a resolution of 5 cm−1 .
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2.4. X-ray Diffraction Almond shells and poplar particles of 60–80 mesh were measured by X-ray diffraction (D/max-2200VPC, Japan science co., Ltd., Takatsuki City, Osaka, Japan) in the range of 2θ = 5–40◦ at scanning speed of 5 rad/cm. Two samples were repeated. The X-ray source was a Cu target (Cu Kα = 1.54056), and a nickel filter was used to excite alpha radiation. The crystallization index of the sample was calculated according to the protocol Formula (1) as follows [24]: CrI (%) =
I002 − Iam × 100% I002
(1)
where I002 is the intensity at 2θ = 22◦ , and Iam is the intensity of background scatter at 2θ = 16◦ . 2.5. Surface Element Almond shells and poplar particles of 60–80 mesh were scanned by an X-ray photo-electron spectrometer (THERMO, American Thermoelectric Group, Waltham, MA, USA). Samples were excited with monochromatic Al Kα rays (1,486.6 eV). The sample binding energy (EB) charge correction was performed using a contaminated carbon C1s (284.8 eV). The X-ray beam was set at 6 mA, and the passing energy was 50 eV. The sputtering ion gun was 1000 eV, and the scanning step was 0.1 eV. Two samples were repeated. 2.6. Thermal Stability The thermal stability of almond shells and poplar particles was measured by high-precision thermo gravimetric analyzer (TG209F1, NETZSCH Scientific Instruments Trading, Bavaria, Germany). The temperature was increased from 0 ◦ C to 800 ◦ C at the rate of 10 ◦ C/min. Two samples were repeated. 2.7. Microscopic Morphology The structure of almond shells was observed by a stereomicroscopic evaluation (JSZ6S, Jiangnan Yongxin Company, Guangzhou, China), and then by scanning electron microscopy (SEM) (QuanTa200, Dutch FEI company, Hillsboro, OR, USA). The cut cross-section of the almond shell was then sprayed with gold and observed at the acceleration voltage of 12.5 kV. 3. Results and Discussion 3.1. Microscopic Morphology Almond shells have well-developed pore structure, as illustrated in Figure 1, where a row of large holes can be seen distributed in the cross section. Diameter of the big holes is 300–500 µm (Figure 1b). The area around the holes is relatively dense; however, it is full of small hollow balls. Under SEM, almond shells appear to be composed of tightly compacted balls from the view of cross section shown in Figure 1c. The diameter of these hollow balls is about 40–60 µm, and thickness of the ball wall is 20–40 µm. When enlarged 3000 times (Figure 1d), tiny holes are found distributed on the wall of balls, and the wall is visibly layered. The almond shell wall is full of holes of varied diameter, making it light and potentially easily absorbed.
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Figure (a)(a) Overall view; (b) (b) Cross-section of shell; (c) Dense partpart of Figure1.1.Almond Almondshell shellmicro-topography. micro-topography. Overall view; cross-section of shell; (c) dense almond shell; (d) Hollow ball in the almond shell. of almond shell; (d) hollow ball in the almond shell.
3.2. Chemical Composition 3.2. Chemical Composition The content of cellulose in almond shells is 38.475%, which is lower than that of poplar (containing The content of cellulose in almond shells is 38.475%, which is lower than that of poplar 44.12% cellulose), but higher than other shells except pistachio shell (Table 1). This indicates that the (containing 44.12% cellulose), but higher than other shells except pistachio shell (Table 1). This mechanical properties of composite prepared by almond shells might be higher than that of most indicates that the mechanical properties of composite prepared by almond shells might be higher biomass nut shells. than that of most biomass nut shells. Table 1. Proportion of cellulose, hemicellulose, lignin in six kinds of biomass (wt %). Table 1. Proportion of cellulose, hemicellulose, lignin in six kinds of biomass (wt %). Sample Cellulose Hemicellulose Lignin
Sample Almond shells Poplar Almond shellsshells Coconut Walnut shells Poplar Chestnut shells Pistachio shells
Coconut shells
Cellulose 38.47 ± 0.39 44.12 ± 0.23 38.47±± 0.20 0.39 34.12 36.38 ± 0.05 44.12±± 0.27 0.23 21.47 43.08 ± 0.19 34.12 ± 0.20
Hemicellulose 28.82 ± 0.25 29.54 ± 0.11 Lignin 30.21 ± 0.11 21.24 ± 0.31 29.54 ± 0.11 22.36 28.82 ± 1.47± 0.25 28.04 ± 0.57 27.85 ± 0.31 43.70 ± 0.57 21.24 ± 0.31 16.28 30.21 ± 0.35± 0.11 36.58 ± 0.26 25.30 ± 0.46 16.33 ± 0.41 22.36 ± 1.47
28.04 ± 0.57
27.85 ± 0.31
43.70 ± 0.57
Note: The data of almond shells and poplar were measured by authors, and the rest of the measurements are derived from literature [25].
Walnut shells
36.38 ± 0.05
Chestnut shells 21.47without ± 0.27 fixed structure; 16.28however, ± 0.35 it is three-dimensional 36.58 ± 0.26 Lignin is an amorphous substance and highly branched. Lignin generally surrounds microfibers and large fibers. The covalent bond between Pistachio shells 43.08 ± 0.19 25.30 ± 0.46 16.33 ± 0.41 lignin and polysaccharide greatly enhances the bonding strength between the cellulose fiber and the The data almond shells and poplar measured The by authors, and the of the ligninNote: matrix, and thusofplays a role in bonding and were strengthening. lignin content of rest almond shells measurements are derived from literature [25]. is 29.54%, higher than that of poplar, which contains 21.24%. Lignin may be beneficial to improve compatibility with thermoplastic, and it has a certain flame-retardant effect which is important for Ligninbeing is an amorphous substance withoutThe fixed structure; is three-dimensional and composites used as building materials. special ring however, structure itand hydroxide structure branched. Lignin agenerally surrounds microfibers The The covalent bond ofhighly hemicellulose produces reactive activity generally higher and thanlarge that offibers. cellulose. content of between lignin and polysaccharide greatly enhances the bonding strength between the cellulose fiber hemicellulose in almond shells and poplar is similar, and higher than other nuts listed in Table 1. and the lignin matrix, and thus plays a role in bonding and strengthening. The lignin content of This indicates that almond shells may have more prospects for modification. almond shells is 29.54%, higher than that of poplar, which contains 21.24%. Lignin may be beneficial The extractive content of almond shells and poplar is presented in Table 2. Extractives from alkali to improve with thermoplastic, haswater. a certain flame-retardant which is method werecompatibility the highest, followed by benzeneand anditcold This result is relatedeffect to solubility composites as building materials. Thewere special ring structure andwas hydroxide inimportant different for solvents. Coldbeing waterused extractives of almond shells 3.14%, and poplar 0.11%. structure of hemicellulose produces a reactive activity generally higher than that of cellulose. The This indicates that almond shells contain more terpenes, phenols, hydrocarbons, and ester compounds content of hemicellulose in almond shells and poplar is similar, and higher than other nuts listed than poplar [26]. Terpenes and phenols are the main component of fragrance, thus almond shells couldin Table 1. This indicates that material almond shells may have moreThe prospects modification. potentially be used as a raw for creating essence. content for of hot water extract was higher The extractive content of almond shells and poplar is presented in Table 2. Extractives from than that of cold water and this is due to the difference in temperature from solubility. alkali method were the highest, followed by benzene and cold water. This result is related to solubility in different solvents. Cold water extractives of almond shells were 3.14%, and poplar was 0.11%. This indicates that almond shells contain more terpenes, phenols, hydrocarbons, and ester compounds than poplar [26]. Terpenes and phenols are the main component of fragrance, thus almond shells could potentially be used as a raw material for creating essence. The content of hot water extract was higher than that of cold water and this is due to the difference in temperature from solubility.
Table 2. Extractive content of different extraction methods (wt(wt %).%). Table 2. Extractive content of different extraction methods Almond Shells Poplar Almond Shells Poplar Table 2. Extractive content of different extraction methods (wt %). Table 2. Extractive content of different extraction methods (wt %). Almond Shells Poplar Almond Shells Poplar Extraction Method Extraction Method Table Extractivecontent content of different extraction methods (wt %). Table 2.2.Extractive of different extraction methods (wt %). Extraction Method Extraction Method ExtractiveContent Content ExtractiveContent Content Extractive Extractive
Almond Shells Poplar Almond Shells Poplar Extractive Content Extractive Content Extractive Content Extractive Content Extraction Method Extraction Method Almond Shells Poplar Almond Shells Poplar Extractive Content Extractive Content Extractive Content Extractive Content Extraction Method Almond Shells Poplar Almond Shells Poplar Extraction Method Cold water extraction 3.14 0.11 Cold water extraction 3.14 0.11 Extractive Content Extractive Content Cold water extraction 3.14 0.11 Cold water extraction 3.14 0.11 Extraction Method Extraction Method Extractive Content Extractive Content Extractive Content Extractive Content Extractive Content Extractive Content Cold water extraction 3.14 0.11 Materials 2018, 11, 1782 5 of 12 Cold water extraction 3.14 0.11 Hot water extraction 4.64 8.64 Hot water extraction 4.64 8.64 Hot water extraction 4.64 8.64 Hot water extraction 4.64 8.64 Cold water extraction 3.14 0.11 Cold water extraction 3.14 0.11 Cold water extraction 3.14 0.11 Cold water extraction 3.14 0.11 Hot water extraction 4.64 8.64 Hot water extraction 4.64 8.64 NaOH (1%) extraction 14.03 20.56 NaOH (1%) extraction 14.03 20.56 NaOH (1%) extraction 14.03 20.56 NaOH (1%) extraction 14.03 20.56 Hot water extraction 4.64 8.64 Hot water extraction 4.64 8.64 Table 2. Extractive content of different extraction methods (wt %). Hot water extraction 4.64 8.64 Hot water extraction 4.64 8.64 NaOH (1%) extraction 14.03 20.56 NaOH (1%) extraction 14.03 20.56 Benzene alcohol extraction 8.00 7.50 Benzene alcohol extraction 8.00 7.50 Benzene alcohol 8.00 7.50 Benzene alcohol extraction 8.00 7.50 NaOH (1%) extraction 14.03 Extraction Method Almond Shells Extractive Content Poplar20.56 Extractive Content NaOH (1%) extraction 14.03 20.56 NaOH (1%) extraction 14.03 20.56 NaOH (1%) extraction 14.03 20.56 Benzene alcohol extraction 8.00 7.50 Benzene alcohol extraction 8.00 7.50 Cold water extraction 3.14 0.11 Benzene alcohol extraction 8.00 7.50 Benzene alcohol extraction 8.00 7.50 Benzene alcohol extraction almond shell was 8.00%, higher than that poplar. This Benzene alcohol of almond shell was 8.00%, aa alittle higher than that of poplar. This Hot waterextraction extraction 4.64 8.64 Benzene alcohol extraction 8.00 7.50 Benzene alcohol extraction 8.00 7.50 Benzene alcohol extraction ofof almond shell was 8.00%, little higher than that ofof poplar. This alcohol extraction of almond shell was 8.00%, alittle little higher than that of poplar. This NaOH (1%) extraction 14.03 20.56 indicates that the almond shells and poplar have similar amounts of colored matter content, such as indicates that the almond shells and poplar have similar amounts of colored matter content, such as Benzene alcohol extraction of almond shell was 8.00%, a little higher than that of poplar. This Benzene alcohol extraction of almond shell was 8.00%, a little higher than that of poplar. This indicates that thethe almond shells and poplar have similar amounts of of colored matter content, such as indicates that almond shells and poplar have similar amounts colored matter content, such as Benzene alcohol extraction 8.00 7.50 Benzene alcohol extraction of of almond shell was 8.00%, athat little higher than that ofalmond poplar. This phlobaphene, tannin, fat, wax and resin. The finding shows there isis potential for almond shells phlobaphene, tannin, fat, wax and resin. The finding shows that is potential for shells Benzene alcohol extraction almond shell was 8.00%, a there little than that of poplar. This indicates that the almond shells poplar have similar amounts of colored matter content, such as indicates that the almond shells and poplar have similar amounts ofhigher colored matter content, such as phlobaphene, tannin, fat, wax and resin. The finding shows that there is potential for almond shells phlobaphene, tannin, fat, wax and resin. The finding shows that there potential for almond shells Benzenealcohol alcoholextraction extractionofofalmond almondshell shellwas was8.00%, 8.00%,a alittle littlehigher higherthan thanthat thatofofpoplar. poplar.This This Benzene indicates that the almond shells and poplar have similar amounts of colored matter content, such as to be used in the production of dye ingredients. to be used in the production of dye ingredients. indicates that the almond shells and poplar have similar amounts of colored matter content, such as phlobaphene, tannin, fat,fat, wax resin. TheThe finding shows that there is potential forfor almond shells phlobaphene, tannin, wax and resin. finding shows that there is potential almond shells toindicates bebe used in in the production ofand dye ingredients. to used the production of dye ingredients. that the almond shells and poplarhave havesimilar similaramounts amountsofofcolored coloredmatter mattercontent, content,such suchasas indicates that the almond shells and poplar phlobaphene, tannin, fat, wax and resin. The finding shows that there is potential for almond shells The NaOH (1%) extraction of almond shell was 14.03%, and was mainly composed of flavonoids, NaOH (1%) extraction of almond shell was 14.03%, and was mainly composed of flavonoids, phlobaphene, tannin, fat, wax and resin. The finding shows that there is potential for almond shells Benzene alcohol extraction of almond shell was 8.00%, a little higher than that of poplar. to be used in the production of dye ingredients. to The be used in the production of dye ingredients. The NaOH (1%) extraction of almond shell was 14.03%, and was mainly composed of flavonoids, The NaOH (1%) extraction of almond shell was 14.03%, and was mainly composed of flavonoids, phlobaphene, tannin, fat,wax waxand and resin.The The finding shows that there potential foralmond almond shells phlobaphene, tannin, fat, resin. finding shows that there isispotential for shells to be used in thethe production of dye ingredients. anthraquinones, phenolic, and lactones. Anthraquinones are antibacterial and have the effects anthraquinones, phenolic, and lactones. Anthraquinones are antibacterial and have the of to be used in production of dye ingredients. This indicates that the almond shells and poplar have similar amounts of colored matter content, The NaOH (1%) extraction of almond shell was 14.03%, and was mainly composed of flavonoids, The NaOH (1%) extraction of almond shell was 14.03%, and was mainly composed ofeffects flavonoids, anthraquinones, phenolic, and lactones. Anthraquinones are antibacterial and have the effects ofof anthraquinones, phenolic, and lactones. Anthraquinones are antibacterial and have the effects of usedininthe theproduction productionofofdye dyeingredients. ingredients. totobebeused The NaOH (1%) extraction of almond shell was 14.03%, and was mainly composed of flavonoids, hemostasis and detoxification, as well as elevating diarrhea and diuresis. Almond shells may also hemostasis and detoxification, as well as elevating diarrhea and diuresis. Almond shells may also The NaOH (1%) extraction of almond shell was 14.03%, and was mainly composed of flavonoids, such as phlobaphene, tannin, fat, wax and resin. The finding shows that there is potential for almond anthraquinones, phenolic, and lactones. Anthraquinones are antibacterial and have the effects of anthraquinones, phenolic, and lactones. Anthraquinones are antibacterial and have the effects of hemostasis and detoxification, as well as elevating diarrhea and diuresis. Almond shells may also hemostasis and detoxification, as well as elevating diarrhea and Almond of shells may also TheNaOH NaOH (1%) extractionofof almond shell was14.03%, 14.03%, and wasdiuresis. mainlycomposed composed offlavonoids, flavonoids, The (1%) extraction almond shell was and was mainly anthraquinones, phenolic, and lactones. Anthraquinones areare antibacterial and have the effects of have this function. have this function. anthraquinones, phenolic, and lactones. Anthraquinones antibacterial and have the effects of hemostasis and detoxification, as well as elevating diarrhea and diuresis. Almond shells may also shells to be used in the production of dye ingredients. hemostasis and detoxification, as well as elevating diarrhea and diuresis. Almond shells may also have this function. have this function. anthraquinones, phenolic,and andlactones. lactones.Anthraquinones Anthraquinonesare areantibacterial antibacterialand andhave havethe theeffects effectsofof anthraquinones, phenolic, hemostasis and detoxification, as well as as elevating diarrhea and diuresis. Almond shells may also The organic compounds contained in benzene alcohol extracts from almond shells were The organic compounds contained in benzene alcohol extracts from almond shells were hemostasis and detoxification, as elevating diarrhea and diuresis. Almond shells may also have this function. The NaOH (1%) extraction ofwell almond shell was 14.03%, and was mainly composed of flavonoids, have this function. The organic compounds contained in benzene alcohol extracts from almond shells were The organic compounds in benzene alcohol extracts from almond shells were hemostasisand anddetoxification, detoxification, ascontained wellasaselevating elevating diarrhea and diuresis. Almond shells may also hemostasis as well diarrhea and diuresis. Almond shells may also have this function. analyzed by mass spectrometry. The results of collecting the compounds with the highest contrast analyzed by mass spectrometry. The results collecting the compounds with the highest contrast have this function. TheThe organic compounds contained in of benzene alcohol extracts from almond shells were anthraquinones, phenolic, and lactones. Anthraquinones are antibacterial and have the effects organic compounds contained in benzene alcohol extracts from almond shells wereof analyzed by mass spectrometry. The results of collecting thethe compounds with the highest contrast analyzed by mass spectrometry. The results of collecting compounds with the highest contrast have thisfunction. function. have this The organic compounds contained in benzene alcohol extracts from almond shells were are presented in Table 3. Almond shells mainly contain 17 kinds of organic compounds, with more are presented in Table 3. Almond shells mainly contain 17 kinds of organic compounds, with more The organic compounds contained in benzene alcohol extracts from almond shells were analyzed by mass spectrometry. The results of collecting the compounds with the highest contrast hemostasis and detoxification, as well as elevating diarrhea and diuresis. Almond shells may also analyzed by mass spectrometry. The results of collecting the compounds with the highest contrast areare presented in in Table 3. 3. Almond shells mainly contain 17 kinds ofof organic compounds, with more presented Table Almond shells mainly contain 17 kinds organic compounds, with more Theorganic organic compounds contained inbenzene benzene alcohol extracts from almondshells shells were The compounds contained in alcohol extracts from almond were analyzed by mass spectrometry. The results of collecting the compounds with the highest contrast ring-based compounds, 10 naphthenic hydrocarbons, two lipids, three olefins, two cyclic-olefins, and ring-based compounds, 10 naphthenic hydrocarbons, two lipids, three olefins, two cyclic-olefins, and analyzed by mass spectrometry. The results of collecting the compounds with the highest contrast are presented in Table 3.10Almond shells mainly contain 17lipids, kinds ofthree organic compounds, with more have this function. are presented in Table 3.10 Almond shells mainly contain 17 kinds ofolefins, organic compounds, with more ring-based compounds, naphthenic hydrocarbons, two three two cyclic-olefins, and ring-based compounds, naphthenic hydrocarbons, two lipids, olefins, two cyclic-olefins, and analyzed by massspectrometry. spectrometry. Theresults results collecting the compounds with the highestcontrast contrast analyzed by mass The ofofcollecting the compounds with the highest are presented inmonocyclic Table 3.10Almond shells mainly contain 17lipids, kinds of organic compounds, with more two kinds of aromatic hydrocarbons. This indicates that the shell contains functional two kinds of monocyclic aromatic hydrocarbons. This indicates that the shell contains functional are presented in Table 3. Almond shells mainly contain 17 kinds of organic compounds, with more ring-based compounds, naphthenic hydrocarbons, two three olefins, two cyclic-olefins, and The organic compounds contained in benzene alcohol extracts from almond shells were analyzed ring-based compounds, 10 naphthenic hydrocarbons, two lipids, three olefins, two cyclic-olefins, and two kinds of of monocyclic aromatic hydrocarbons. This indicates that thethe shell contains functional two kinds monocyclic aromatic hydrocarbons. This indicates that shell contains functional are presented Table3.3.Almond Almond shells mainlycontain contain kindsof oforganic organic compounds, with more are presented inin Table shells mainly 1717 kinds compounds, with more ring-based compounds, 10 naphthenic hydrocarbons, two lipids, three olefins, two cyclic-olefins, and groups and active chemical properties. In Table 3, it can be seen that there are more naphthenic groups and active chemical properties. In Table 3, it can be seen that there are more naphthenic ring-based compounds, 10 naphthenic hydrocarbons, two lipids, three olefins, two cyclic-olefins, and two kinds of monocyclic aromatic hydrocarbons. This indicates that the shell contains functional by mass spectrometry. The results of collecting the compounds with the highest contrast are presented two kinds ofactive monocyclic aromatic hydrocarbons. This indicates that the shell contains functional groups and active chemical properties. InIn Table 3, 3, ittwo can bebe seen that there are more naphthenic groups and chemical properties. Table it can seen that there are more naphthenic ring-based compounds, naphthenic hydrocarbons, two lipids, three olefins, two cyclic-olefins, and ring-based compounds, 1010naphthenic hydrocarbons, lipids, three olefins, two cyclic-olefins, and two of3. monocyclic aromatic hydrocarbons. This that the shell contains functional hydrocarbons in the almond shells, so ithas has the potential to be used as araw raw material for fuel, hydrocarbons in the almond shells, so it the to be used as aathere material for fuel, or to two kinds of monocyclic aromatic hydrocarbons. indicates that the shell contains functional groups and active chemical properties. In Table 3, it can be seen that are more naphthenic inkinds Table Almond shells mainly contain 17potential kinds of organic compounds, with more ring-based groups and active chemical properties. In Table 3,This itindicates can be seen that there are more naphthenic hydrocarbons in the almond shells, so it has the potential to be used as raw material for fuel, oror toto hydrocarbons in the almond shells, so it has the potential to be used as a raw material for fuel, or to twokinds kindsofofmonocyclic monocyclicaromatic aromatichydrocarbons. hydrocarbons.This Thisindicates indicatesthat thatthe theshell shellcontains containsfunctional functional two groups and active chemical properties. In Table 3, it can be seen that there are more naphthenic prepare cosmetics. prepare cosmetics. groups and active chemical properties. In Table 3, it can be seen that there are more naphthenic hydrocarbons in the almond shells, so it has the potential to be used as a raw material for fuel, or to compounds, 10 naphthenic hydrocarbons, two lipids, three olefins, two cyclic-olefins, and two kinds hydrocarbons in the almond shells, so it has the potential to be used as a raw material for fuel, or to prepare cosmetics. prepare cosmetics. groups and activechemical chemicalproperties. properties.InInTable Table3,3,ititcan canbebeseen seenthat thatthere thereare aremore morenaphthenic naphthenic groups and active hydrocarbons in the almond shells, so it has the potential to be used as a raw material for fuel, or to hydrocarbons in the almond shells, so it has the potential to be used as a raw material for fuel, or to prepare cosmetics. of monocyclic aromatic hydrocarbons. This indicates that the shell contains functional groups and prepare cosmetics. hydrocarbonsininthe thealmond almond shells, hasthe the potential used araw rawmaterial materialfor forfuel, fuel,orortoto hydrocarbons shells, sosoitithas potential totobebe used asasashells. Table3.3. Compound containing extracts of almond shells. Table containing of almond prepare prepare cosmetics. activecosmetics. chemical properties. Table 3,shell itshell can be seen extracts that there are more naphthenic hydrocarbons in 3. Compound Compound shell containing extracts of of almond shells. Table 3.In Compound shell containing extracts almond shells. preparecosmetics. cosmetics. Table prepare 3. Compound shell extracts almond shells. 3. Compound shell of almond shells. the almond shells, Table so Table it has the potential tocontaining becontaining used as aextracts rawof material for fuel, or to prepare cosmetics.
Chemical Molecular Structural Chemical Molecular Chemical Molecular Structural Chemical Molecular Table 3. Compound shell containing extracts of almond shells. Table 3. Compound shell containing extracts of almond shells. Chemical Molecular Structural Chemical Molecular Chemical Molecular Structural Chemical Molecular Table 3. Compound shell containing extracts of almond shells. Table 3. Compound shell containing extracts of almond shells. Compound Formula Formula Compound Formula Compound Formula Formula Compound Formula Chemical Molecular Structural Chemical Molecular Chemical Molecular Structural Chemical Molecular Compound Formula Formula Compound Formula Compound Formula Formula Compound Formula Table 3. Compound shell containing extracts of almond shells. Chemical Molecular Structural Chemical Molecular Compound Formula Formula Compound Formula Chemical Molecular Structural Chemical Molecular Compound Formula Formula Compound Formula Chemical Molecular Structural Chemical Molecular Chemical Molecular Structural Chemical Molecular Cyclohexane,1, Cyclohexane,1, Compound Formula Formula Compound Formula Compound Formula Formula Compound Formula Chemical Molecular Structural Chemical Molecular Cyclohexane,1, Cyclohexane,1, Cyclopentane, Cyclopentane, Cyclopentane, Cyclopentane, Compound Formula Formula Compound Formula Compound Formula Formula Compound Formula C7H 14 2-dimethyl-, CH8H 16 C 2-dimethyl-, C Compound Formula Formula Compound Cyclohexane,1, Cyclohexane,1, C77H H714 14 2-dimethyl-, C88Formula H816 16 C H14 2-dimethyl-, C H16 ethylethylCyclopentane, Cyclopentane, ethylethylciscisCyclohexane,1, C7H 2-dimethyl-, C8H Cyclohexane,1, C147H14 2-dimethyl-, C168H16 cis-cisCyclopentane, ethylCyclopentane, ethylCyclohexane,1, Cyclohexane,1, C7H 2-dimethyl-, C8H cis-cisC14 7H14 2-dimethyl-, C16 8H16 Cyclopentane, Cyclopentane, Cyclopentane, Cyclohexane,1, ethylethylH16 C 2-dimethyl-, 8C H CC 7H 1414 2-dimethyl-, 8H 16 77H 14 816 cis-cis- cis- CC ethyl2-dimethyl-, ethylethylCyclohexane, Cyclohexane, ciscisCyclohexane, Cyclohexane, Toluene C7H 8 C8H 16 Toluene C C Toluene C77H H788H8 C88H H816 16 Toluene C C H16 ethylethylCyclohexane, Cyclohexane, ethylethylToluene C7H C8H Toluene C87H8 C168H16 Cyclohexane, ethylCyclohexane, ethylToluene CC 7H 87H C8H Toluene Toluene C CC16 88 HH1616 Cyclohexane, Cyclohexane, 7H 88 ethylethylToluene 7H 8H Toluene CC 7H 8 8 CC 8H 1616 ethylethylCyclohexane,1,31,3Cyclohexane, Cyclohexane, Cyclohexane, Cyclohexane, 1,3Cyclohexane, Cyclohexane, 1,3Cyclohexane, 16 C9H 18 C8H C C H816 16 C99H H918 18 C88H H16 C H18 C Cyclohexane, 1,1,3-trimethyl dimethyl-, cis1,1,3-trimethyl dimethyl-, cisCyclohexane, 1,3Cyclohexane, Cyclohexane, 1,31,1,3-trimethyl dimethyl-, cisCyclohexane, 1,1,3-trimethyl dimethyl-, cis8 H 16 C 9 H 18 C 8H C C99H H1818 1,3-dimethyl-, CC 8H 1616 Cyclohexane, 1,3Cyclohexane, 1,1,3-trimethyl dimethyl-, cisCyclohexane, 1,3Cyclohexane, 1,1,3-trimethyl 1,1,3-trimethyl dimethyl-, cisC9H C8H cis8H16 C18 9H18 C16 Cyclohexane, 1,3Cyclohexane, Cyclohexane, 1,3Cyclohexane, 1,1,3-trimethyl dimethyl-, cis-cis1,1,3-trimethyl dimethyl-, 8H 9H 8H 1616 CC 9H 1818 CC 1,1,3-trimethyl dimethyl-,ciscis1,1,3-trimethyl dimethyl-, Cyclohexane,1,11,1Cyclohexane, Cyclohexane, 1,1Cyclohexane, 1,1Cyclohexane, 8H Ethylbenzene C8H 10 8C H 16 16 Ethylbenzene C C 8C H Ethylbenzene C88H HC810 10 CC 816 H1616 Ethylbenzene C H 1010 dimethyldimethyl8H 8H Cyclohexane, 1,1Cyclohexane, 1,1dimethyl1,1-dimethyldimethylEthylbenzene C8H C8H Ethylbenzene C108H10 C168H16 Cyclohexane, 1,1-1,1dimethylCyclohexane, dimethylEthylbenzene C8H C8H 8H16 Ethylbenzene C10 8H10 C16 Cyclohexane, 1,1Cyclohexane, 1,1dimethyldimethyl8H Ethylbenzene 8H 8H 1616 Ethylbenzene CC 8H 1010 CC CisCisdimethyldimethylCisCisCyclopentane,1Cyclopentane,1Cyclopentane,1 Cis-bicyclo[4.2.0] Cyclopentane,1Cyclopentane,116 bicyclo[4.2.0]oc C8CH C 8C H 16 16 bicyclo[4.2.0]oc C H1414 88H 8 14 CisMaterials 2018, x FOR PEER REVIEW CisMaterials 2018, 11, 11, x FOR PEER REVIEW CC 8C H bicyclo[4.2.0]oc C88H H814 14 816 H16 bicyclo[4.2.0]oc C H ethyl-3-methyl-ethyl-3-methyloctane ethyl-3-methylCyclopentane,1Cyclopentane,1ethyl-3-methylethyl-3-methyltane tane CisC8H bicyclo[4.2.0]oc C8H CisC168H16 bicyclo[4.2.0]oc C148H14 tane tane Cyclopentane,1ethyl-3-methylCyclopentane,1ethyl-3-methylCisCisC8H bicyclo[4.2.0]oc C8H tane C16 8H16 bicyclo[4.2.0]oc C14 8H14 tane Cyclopentane,1Cyclopentane,1ethyl-3-methylethyl-3-methyl8H bicyclo[4.2.0]oc 8H CC 8H 1616 bicyclo[4.2.0]oc CC 8H 1414 (Z)-Hex-3-enyl Hexane,3tane (Z)-Hex-3-enyl (E)-(E)Hexane,3tane (Z)-Hex-3-enyl(E) ethyl-3-methylethyl-3-methylHexane,3-methyltane tane 2-methylbut-2C 11 O2 2 methyl-4C -2-methylbut-2- CC1111 C1688H H1616 2-methylbut-2HH 18H O 2O methyl-4C8H 1818 4-methyleneenoate enoate methyleneenoate methylene-
Cyclohexane,1,3Cyclohexane,1,3dimethyl-, dimethyl-, cis-cis-
C168H16 C8H
Cyclohexane, Cyclohexane, ethenylethenyl-
C148H14 C8H
Butanoicacid,2Butanoicacid,2methyl-,1,2methyl-,1,2dimethylpropyl dimethylpropyl ester ester
C10C H1020H O202 O2
Cyclopentane, Cyclopentane, (1- (1methylethyl)methylethyl)-
C168H16 C8H
Structural Structural Structural Structural Formula Formula Structural Structural Formula Formula Structural Formula Structural Formula Structural Structural Formula Formula Structural Formula Formula Formula
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Materials x FOR REVIEW Materials 2018,2018, 11, x11, FOR PEERPEER REVIEW Materials 2018, x FOR PEER REVIEW Materials 2018, 11,11, x FOR PEER REVIEW Materials 2018, 11,11, x FOR PEER REVIEW Materials 2018, x FOR PEER REVIEW Materials 2018, 11, 1782
(Z)-Hex-3-enyl (Z)-Hex-3-enyl (E)- (E)(Z)-Hex-3-enyl (E)(Z)-Hex-3-enyl (E)2-methylbut-22-methylbut-2(Z)-Hex-3-enyl (E)(Z)-Hex-3-enyl (E)2-methylbut-22-methylbut-2enoate enoate 2-methylbut-22-methylbut-2enoate enoate enoate enoate Chemical Compound Cyclohexane,1,3Cyclohexane,1,3Cyclohexane,1,3Cyclohexane,1,3dimethyl-, dimethyl-, cis- cisCyclohexane,1,3Cyclohexane,1,3Cyclohexane,1,3dimethyl-, dimethyl-, cis-cisdimethyl-, cisdimethyl-, dimethyl-, cis- cisButanoicacid,2Butanoicacid,2Butanoicacid,2Butanoicacid,2methyl-,1,2Butanoicacid,2methyl-,1,2Butanoicacid,2Butanoicacid,2methyl-,1,2methyl-,1,2methyl-,1,2dimethylpropyl dimethylpropyl methyl-,1,2methyl-,1,2dimethylpropyl dimethylpropyl dimethylpropyl ester ester dimethylpropyl dimethylpropyl ester ester ester ester ester Cyclohexane,1,4Cyclohexane,1,4Cyclohexane,1,4Cyclohexane,1,4Cyclohexane,1,4dimethyldimethyldimethylCyclohexane,1,4Cyclohexane,1,4dimethyldimethyldimethyldimethyl-
C11HC1811OH2 18O2 C11CH1118HO182O2 C11CH 1118 HO 182O2 Molecular Formula C8HC 16 8H16 C8C H816H16 CC 8C H 16 H16 16 88H
C10HC2010OH2 20O2 CH10 CC1010 O20O 2O H20H 20 22 C10CH 1020 HO 202O2
Hexane,3Hexane,3Hexane,3Hexane,3methyl-4methyl-4Hexane,3Hexane,3methyl-4methyl-4methyleneTable 3. Cont. methylenemethyl-4methyl-4methylenemethylenemethylenemethyleneStructural Chemical Formula Compound Cyclohexane, Cyclohexane, Cyclohexane, Cyclohexane, ethenylethenylCyclohexane, Cyclohexane, Cyclohexane, ethenylethenylethenylethenylethenylCyclopentane, Cyclopentane, Cyclopentane, Cyclopentane, (1- (1Cyclopentane, Cyclopentane, Cyclopentane, (1-(1methylethyl)methylethyl)(1-methylethyl)(1-(1methylethyl)methylethyl)methylethyl)methylethyl)-
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C8HC 16 8H16 C8C H816H16 C8C H816 H16 Molecular Formula C8HC 14 8H14 C8C H814H14 C8C HC 814 H 14 14 8H
Structural Formula
C8HC 16 8H16 C8C H C816 H1616 8H C8C H816 H16
C H16 CC 8H 16 816 8H C8C H816H16 C8C H816 H16
Infrared Spectrum 3.3. Infrared Spectrum 3.3.3.3. Infrared Spectrum 3.3. Infrared Spectrum 3.3. Infrared Spectrum The Fourier-transform infrared (FTIR) spectra of almond shells in 22 and 3.3. Infrared Spectrum The Fourier-transform infrared (FTIR) spectra of poplar poplar and almond shells seen in Figure Figure and 3.3. Infrared Spectrum The Fourier-transform infrared (FTIR) spectra of poplar andand almond shells seenseen in Figure 2 and The Fourier-transform infrared (FTIR) spectra of poplar and almond shells seen in Figure 2 and The Fourier-transform infrared (FTIR) spectra of poplar and almond shells seen in Figure 2 and Table 4 are alike, reflecting that they share similar chemical components, which are mainly cellulose, Table 4 are alike, reflecting that they share similar chemical components, which are mainly cellulose, TableThe 4The are alike, reflecting that they (FTIR) share similar chemical components, which are mainly cellulose, infrared spectra ofchemical poplar and almond shells seen in Figure 2 and Fourier-transform infrared (FTIR) spectra of poplar and almond shells seen in Figure 2 and Table 4Fourier-transform are alike, reflecting that they share similar components, which are mainly cellulose, Table 4 are alike, reflecting that they share similar chemical components, which are mainly cellulose, hemicellulose, and lignin. The peak range and sharpness are different and illustrate the content hemicellulose, and lignin. The peak range and sharpness are different and illustrate the content hemicellulose, and lignin. The peak range and sharpness are different and illustrate the content Table 4 are alike, reflecting that they share similar chemical components, which are mainly cellulose, Table 4 are alike, reflecting that they share similar chemical components, which are mainly cellulose, −illustrate 1 for poplar hemicellulose, and lignin.The The peak rangeand and sharpness different and the hemicellulose, lignin. peak range sharpness areare different and illustrate the content −1 for difference of their components. For example, the characteristic peak ofof890 cm is sharper −1 difference ofand their components. For example, the characteristic peak 890 cm poplar iscontent sharper difference of their components. For example, the characteristic peak of 890 cm for poplar is sharper hemicellulose, and lignin. The range sharpness are different and illustrate the hemicellulose, and lignin. Thepeak peak rangeand and sharpness are different and illustrate the content −1 −1 difference their components. For example, the characteristic peak 890 cm for poplar is sharper difference ofof their components. For example, the characteristic peak ofof 890 cm for poplar is content sharper than almond shells. This is characteristic peak of indicating that poplar contains more than almond shells. This is the the characteristic peak of cellulose, cellulose, indicating that poplar contains more than almond shells. This is the characteristic peak of cellulose, indicating that contains more −1poplar −1 difference of their components. For example, the characteristic peak of 890 cm for poplar is sharper difference of their components. For example, the characteristic peak of 890 cm for poplar is sharper − 1 − 1 than almond shells. This is the characteristic peak of cellulose, indicating that poplar contains more than almond shells. This is the characteristic peak of cellulose, indicating that poplar contains more −1 −1 cellulose than almond shells (as Table 1). The characteristic peak at 1580 cm and 820 cm of almond −1 −1 cellulose almond shells (as Table 1). The characteristic peak at 1580 cm and cm of almond cellulose thanthan almond shells (as Table 1). The characteristic peak at 1580 cmthat and 820 820 cm of almond than almond shells. This is is the characteristic peak ofof cellulose, indicating contains more than almond shells. This the characteristic peak cellulose, indicating that poplar contains more −1poplar −1 of −1 −1 of cellulose than almond shells (as Table 1). The characteristic peak at 1580 cm and 820 cm almond cellulose than almond shells (as Table 1). The characteristic peak at 1580 cm and 820 cm almond shells is sharper and stronger than poplar, giving evidence that almond shells contain more lignin shells is sharper and stronger than poplar, giving evidence that almond shells contain more lignin shells is sharper and stronger than poplar, giving evidence that almond shells contain more lignin −1 −1 −1 −1 cellulose than almond shells (as(as Table 1). The characteristic peak atalmond 1580 cm and 820 cm ofmore almond cellulose than almond shells Table 1). The characteristic peak at 1580 cm and 820 cmmore of almond −−1 1 of shells is sharper and stronger than poplar, giving evidence that almond shells contain lignin shells is sharper and stronger than poplar, giving evidence that shells contain lignin than poplar. The characteristic peak at 1730 cm the two samples was similar, indicating that −1 than poplar. characteristic peak at 1730 cm of the samples similar, indicating that the than poplar. TheThe characteristic peak atpoplar, 1730 cm ofevidence the twotwo samples waswas similar, indicating that the the shells ispoplar. and stronger than poplar, giving that almond shells contain more lignin shells issharper sharper and stronger than giving evidence that almond shells contain more lignin −1 of −1 of than The characteristic peak at 1730 cm the two samples was similar, indicating that than poplar. The characteristic peak at 1730 cm the two samples was similar, indicating that thethe hemicellulose content is much the same [27]. hemicellulose content is much the same [27].−1 −1 hemicellulose content is much the same [27]. than poplar. The characteristic peak at 1730 cm the two samples was similar, indicating that the than poplar. The characteristic peak at 1730 cm ofof the two samples was similar, indicating that the hemicellulose content much the same [27]. hemicellulose content is is much the same [27]. hemicellulose content is is much the same [27]. hemicellulose content much the same [27].
Figure 2. spectra. 2. Infrared Figure 2. Infrared spectra. Figure 2. Infrared spectra. Figure 2. Infrared spectra. Figure 2. 2. Infrared spectra. Figure Infrared spectra.
2900~2935
–CH
stretching vibration
-
1640~1735
C=O
stretching vibration
lignin, hemicellulose
benzene ring
stretching vibration
lignin
–CH3O
stretching vibration
lignin
1580~1605 Materials 2018, 11, 1782 1455~1465
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Table 4. Absorption band assignment in the infrared spectrum of almond shell and poplar.
1320~1430 Wavenumber
(cm−1 )
1221~1230
3300~3500 2900~2935 1640~1735 1025~1035 1580~1605 1455~1465 885~895 1320~1430 1221~1230 1025~1035 810~833 885~895 810~833
–CH
Functional Group
C–C C–O
bending vibration
Vibration Type
stretching vibration
-
Cause
lignin
–OH stretching vibration cellulose, hemicellulose –CH stretching vibration cellulose, hemicellulose, and C=O C–O stretching vibration lignin, hemicellulose stretching vibration lignin benzene ring stretching vibration lignin –CH3 O stretching vibration lignin bending vibration R2C=CH2 –CH bending vibration - C–C C–O stretching vibration lignin disubstituted cellulose, hemicellulose, and lignin C–O benzene ring stretching vibration R2 C=CH2 bending vibration benzene benzene ring disubstituted benzene -
3.4. X-ray Diffraction 3.4. X-ray Diffraction The X-ray diffraction curves in Figure 3 show that the diffraction peaks of almond shells The X-ray diffraction curves in Figure 3 show that the diffraction peaks of almond shells appeared appeared◦ near 16.6°, 21.48° and 34.67°, indicating its cellulose crystals belong to cellulose I type. In near 16.6 , 21.48◦ and 34.67◦ , indicating its cellulose crystals belong to cellulose I type. In addition, addition, using height method [28] to calculate the crystallization, the crystallization of almond shells using height method [28] to calculate the crystallization, the crystallization of almond shells is 32.88% is 32.88% lower than that of poplar (48.166%). Crystallization is mainly caused by cellulose, so low lower than that of poplar (48.166%). Crystallization is mainly caused by cellulose, so low crystallization crystallization may result in a decrease of mechanical properties. However, compared with other may result in a decrease of mechanical properties. However, compared with other commonly used commonly used nuts, crystallization of almond shells is higher, for example, crystallization is 23.25% nuts, crystallization of almond shells is higher, for example, crystallization is 23.25% for chestnut shells, for chestnut shells, 26.85% for peanut shells, 29.11% for melon shells, 30.61% for macadamia shells, 26.85% for peanut shells, 29.11% for melon shells, 30.61% for macadamia shells, and 23.69% for walnut and 23.69% for walnut shells [29]. Combined with cellulose content, almond shells may present shells [29]. Combined with cellulose content, almond shells may present higher mechanical properties higher mechanical properties than other nut shells, which is beneficial in the preparation of than other nut shells, which is beneficial in the preparation of composite. composite.
Figure 3. X-ray diffraction spectra.
3.5. X-ray Photoelectron Spectroscopy Characterization As shown in Figure 4, both almond shells and poplar have strong peaks near 532.39 eV/285 eV in X-ray photoelectron spectroscopy, which is the peak of O 1s and C 1s, respectively. In addition, the peak position of N was detected at 398 eV in almond shells, while the peak position of Si at 101.8 eV was detected in poplar. This indicates that there are more N elements in almond shells and Si elements in poplar, and the N may be contained in the protein.
3.5. X-ray Photoelectron Spectroscopy Characterization As shown in Figure 4, both almond shells and poplar have strong peaks near 532.39 eV/285 eV in X-ray photoelectron spectroscopy, which is the peak of O 1s and C 1s, respectively. In addition, the peak position of N was detected at 398 eV in almond shells, while the peak position of Si at 101.8 eV was detected in poplar. This indicates that there are more N elements in almond shells and Materials 2018, 11, 1782 8 of 12Si elements in poplar, and the N may be contained in the protein.
Figure4.4.X-ray X-rayphotoelectron photoelectronspectroscopy. spectroscopy. Figure
Table mainchemical chemicalelements elementscontained containedinin the almond shells essentially Table55shows shows that the main the almond shells areare essentially the the same as those in other Compared with theof shell of Chinese chestnut, Sunflower, same as those in other nuts.nuts. Compared with the shell Chinese chestnut, peanut,peanut, Sunflower, Hawaii Hawaii nut, and walnut, shells present the highest of oxygen, and relatively low nut, and walnut, almondalmond shells present the highest contentcontent of oxygen, and relatively low carbon carbon content. Compared to poplar, nut shells generally contain less silicon and more nitrogen content. Compared to poplar, nut shells generally contain less silicon and more nitrogen elements. elements. Almond shells might therefore have advantages in fire resistance when preparing composite, Almond shells might therefore have advantages in fire resistance when preparing composite, due to due the flame inhabitant capabilities the to flame inhabitant capabilities of N. of N. Table Table5.5.Surface Surfacechemical chemicalcomposition compositionand andrelative relativecontent contentofofnut nutand andpoplar poplar(wt (wt%). %). Sample Typen C Sample Type Chestnut shells Chestnut shells 80.26 Peanut shells Sunflower shells Peanut shells 74.16 Hawaii nut shells Walnut shell Sunflower shellsPoplar 78.86 Almond shells
Hawaii nut shells
79.16
nC
nO nO
80.26 17.28 74.16 17.2821.72 78.86 18.13 79.16 21.7218.92 78.84 19.32 74.56 18.1320.93 72.27 22.88
18.92
n sin si
nN
0.85 0.340.85 0.42 0.260.34 0.16 4.510.42 0.87
1.61 3.78 2.59 1.67 1.67 3.87
0.26
nN 1.61 3.78 2.59 1.67
Note: The data of almond shells are measured by authors, and the rest are derived from reference [29].
Walnut shell 78.84 19.32 0.16 1.67 The software XPS Pesk was used to fit the peak of the curve for Figure 5, and C1 , C2 , and C3 Poplar the different 74.56 20.93 The main form 4.51of carbon in almond was used to represent states of carbon. shells is C1 , C2 , andAlmond C3, as listed in Table 6. The characteristic peak of binding energy 284.38 eV was mainly shells 72.27 22.88 0.87 3.87 produced by C–H bond in Figure 5. Its electronegativity was small, so the binding energy was small. Note: The data of almond shells are measured by authors, and the rest are derived from reference The characteristic peak of binding energy 286.08 eV was mainly produced by C–OR, in which binding [29]. energy was higher. The binding energy of C3 (287.79 eV) was mainly produced by C=O. In Table 6, C2 content of almond shells was higher than that of other biomass nut shells, The software XPS Pesk was used to fit the peak of the curve for Figure 5, and C1, C2, and C3 was indicating that there are more –OR groups in the almond shells. This result is consistent with Table 1, used to represent the different states of carbon. The main form of carbon in almond shells is C1, C2, showing that almond shells were likely to contain more cellulose. The content of C3 is lower than that and C3, as listed in Table 6. The characteristic peak of binding energy 284.38 eV was mainly produced of other biomass nut shells, which illustrates that the C=O in the almond shell was less than that of by C–H bond in Figure 5. Its electronegativity was small, so the binding energy was small. The other biomass nut shells.
characteristic peak of binding energy 286.08 eV was mainly produced by C–OR, in which binding energy was higher. The binding energy of C3 (287.79 eV) was mainly produced by C=O. In Table 6, C2 content of almond shells was higher than that of other biomass nut shells, indicating that there are more –OR groups in the almond shells. This result is consistent with Table 1, showing that almond shells were likely to contain more cellulose. The content of C3 is lower than Materials 2018, 11, 1782 that of other biomass nut shells, which illustrates that the C=O in the almond shell was less than that of other biomass nut shells.
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5. High-resolution maps of shells. Figure Figure 5. High-resolution C C1s1smaps ofalmond almond shells. Table photoelectron 6. X-ray photoelectron spectroscopy (XPS)test test results of of almond shellsshells C 1s. C 1s. Table 6. X-ray spectroscopy (XPS) results almond
Binding Energy (eV)
Sample
Sample
AlmondAlmond shells shells Chestnut shells shells Chestnut Peanut shells Peanut shells Sunflower shells Hawaii nut shellsshells Sunflower Walnut shells
Hawaii nut shells
A (%)
Binding Energy (eV)
A (%)
C1 1s
C1 1s
1s CC2 21s
CC33 1s 1s
C1 1s C 1 1s
C2 1s C2 1s
C3 1s C3
284.38 284.38 284.8 284.8 284.8 284.8 284.8 284.8 284.8 284.8
286.08 286.08 286.28 286.28 286.24 286.24 286.25 286.25 286.25 286.25
287.79 287.79 286.93 286.93 286.79 286.79 288.07 287.70 288.07 287.10
55.88 55.88
32.35 32.35
11.76 11.76
63.18 63.18
17.70 17.70
19.12 19.12
48.93 48.93 61.99 54.58 61.99 55.22
16.34 16.34 25.94 30.85 25.94 23.17
284.8
286.25
287.70
54.58
30.85
1s
34.73 12.07 14.57 12.07 21.61 34.73
14.57
Note: The data of almond shells are measured by authors, the rest of the data is derived from reference [29]. Walnut shells
3.6. Thermal
284.8
286.25
287.10
55.22
23.17
21.61
Note: The data of almond shells are measured by authors, the rest of the data is derived from reference Stability [29].
The pyrolysis process of almond shells is presented in Figure 6. From room temperature to 200 ◦ C, 3.6. Thermal Stability almond shells and poplar have a small weight loss peak due to the water loss stage. In the range of Thepoplar pyrolysis process of almond shells is presented in Figure From room temperature to 200 200–350 ◦ C, both and almond shells display a weight loss6. peak which is mainly formed by °C, almond shells and poplar have a small weight loss peak due to the water loss stage. In the range hemicellulose and lignin. Weight loss of almond shells occurred earlier than poplar, however, and the of 200–350 °C, both poplar and almond shells display a weight loss peak which is mainly formed by Materials 2018, 11, x FOR PEER REVIEW 10 of 12 peak of the almond shells was sharper poplar. highest loss peaks ofpoplar, poplarhowever, and almond shells hemicellulose and lignin. Weightthan loss of almondThe shells occurred earlier than and ◦ C, peak of ◦the shellsoccurs was than The loss peaks of poplar and stage. almond appeared atthe 300–500 C.almond The poplar hadsharper the highest peak at highest 350 while the almond shell peak was The carbonization phase after 500 °C poplar. and pyrolysis is basically completed at this shells at wider 300–500 °C. The poplar had the peak 350 °C, while the almond shell theappeared curve of is nutrient biomass after 500 °C tends tohighest be gentle. In at conclusion, the thermal stability at 338 ◦ C. Thus, Poplar’s peak and sharper than almond shells. Thermal interpretation of cellulose peak was at 338 °C. Poplar’s peak is wider and sharper than almond shells. Thermal interpretation of poplar is superior to that of almond shells, but compared with other nut shells, the thermal stability and lignin isofformed by volatiles, mainly relying on the pyrolysis of celluloseof[30]. The [30]. higher peaks of cellulose and by the volatiles, relying on the pyrolysis The of almond shells is lignin better,is forformed example, highestmainly pyrolysis temperature of pistachiocellulose shells is 337 °C, poplar indicate that it contains more cellulose. higher peaks poplar indicate that itiscontains more and cashew nutof shells is 318 °C, which lower than thecellulose. almond shells (338 °C).
6. Thermal gravityand and derivative thermogravimetric. FigureFigure 6. Thermal gravity derivative thermogravimetric.
4. Conclusions In this study, the physical structure and chemical properties of almond shells were determined. The following conclusions were obtained. 1. 2.
Observed by microscope and electron microscope, almond shells have the diameter of 300–500 μm for large holes, and 40–60 μm for small holes. The elements of almond shells include C (72.27%), O (22.88%), N (3.87%), and Si (0.87%). The
Materials 2018, 11, 1782
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The carbonization phase occurs after 500 ◦ C and pyrolysis is basically completed at this stage. Thus, the curve of nutrient biomass after 500 ◦ C tends to be gentle. In conclusion, the thermal stability of poplar is superior to that of almond shells, but compared with other nut shells, the thermal stability of almond shells is better, for example, the highest pyrolysis temperature of pistachio shells is 337 ◦ C, and cashew nut shells is 318 ◦ C, which is lower than the almond shells (338 ◦ C). 4. Conclusions In this study, the physical structure and chemical properties of almond shells were determined. The following conclusions were obtained. 1. 2.
3.
4.
5.
6.
Observed by microscope and electron microscope, almond shells have the diameter of 300–500 µm for large holes, and 40–60 µm for small holes. The elements of almond shells include C (72.27%), O (22.88%), N (3.87%), and Si (0.87%). The main chemical constituents of cellulose, hemicellulose, and lignin account for 38.48%, 28.82% and 29.54%. The alkaline extract content of almond shells was 14.03%, and benzene alcohol extraction was 8.00%. The benzene alcohol extractives of almond shells mainly contain 17 types of organic compound including benzene ring, methylene, carbon three bond, and other multi-functional groups. Thermogravimetric analysis shows almond shells mainly lose weight at 260 ◦ C and 335 ◦ C. This shows that its pyrolysis temperature is lower than poplar; however, it is higher than pistachio shells and cashew nut shells. X-ray diffraction spectra showed that diffraction peaks of almond shells appeared near 16.6◦ , 21.48◦ and 34.67◦ . Cellulose crystals belong to cellulose I type. The crystallization of almond shells is 32.88%, which is lower than poplar; however, it is higher than chestnut shells, peanut shells, melon shells, macadamia shells, and walnut shells. X-ray photoelectron spectroscopy showed that almond shells contained more N than poplar and five other kinds of nut shell (chestnut shells, peanut shells, sunflower shells, Hawaii nut shells, and walnut shells). There was less Si in the almond shells compared to poplar.
Author Contributions: Conceptualization, W.W. and X.L.; Methodology, X.L.; Software, J.H.; Validation, X.L.; J.H. and Y.L.; Formal Analysis, X.L. and Y.L.; Investigation, X.L.; Resources, X.L.; Data Curation, X.L. and Y.L.; Writing-Original Draft Preparation, X.L. and Y.L.; Writing-Review & Editing, X.L. and W.W.; Visualization, X.L. and W.W.; Supervision, X.L. and W.W.; Project Administration, W.W.; Funding Acquisition, W.W. Funding: This research was funded by [Nature Science Foundation of China] grant number [31670573] and the 2017 Special Project of Sustainable Development for Central University Innovation Team of the Ministry Education grant number [2572017ET05]. Acknowledgments: The authors would like to acknowledge the financial support by the Nature Science Foundation of China (31670573) and the 2017 Special Project of Sustainable Development for Central University Innovation Team of the Ministry Education (2572017ET05). Conflicts of Interest: The authors declare no conflict of interest.
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