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Yu et al. (2025). “Walnut powder DLP 3D printing,” BioResources 20(3), 5348-5360.  5348 

 

Effects of Walnut Shell Powder Content on the Molding 
Performance of Digital Light Processing 3D Printed 
Parts  
 
Yueqiang Yu,a,b Shaorui Shen,a Sheng Gao,a,b,* Ting Jiang,a,b Tao Qin,a Junyuan Chen,a 

Chenxiang Yuan,a and Junkai Zhang a 

 
Additive Manufacturing (AM) is a digital manufacturing method that 
creates structures by adding material layer by layer. This approach offers 
simplicity, speed, and efficiency. Additive manufacturing methods can 
process wood-plastic composites, but they are often limited by poor 
surface quality, low interfacial bonding, and the requirement for complex 
post-processing. In this study, walnut shell and photosensitive resin were 
used to fabricate wood-plastic composite specimens with varying walnut 
shell powder contents using DLP technology. The properties analyzed 
included dimensional shrinkage, mechanical strength, double bond 
conversion rate, and microstructure. The results indicated that as the 
walnut shell content increased, the dimensional shrinkage of the formed 
parts initially decreased and then increased, reaching the minimum value 
of 0.631% at 12% walnut shell powder content. SEM imaging revealed 
that resin infiltrates the particle pores, forming a network structure that 
enhances mechanical performance. Tensile and flexural strengths also 
reached their peak values at 8% content, measuring 17.7 and 45.4 MPa, 
respectively, while impact strength decreased with increasing walnut shell 
content. 
 

DOI: 10.15376/biores.20.3.5348-5360 

 

Keywords: 3D printing; Biomass composite; Walnut shell powder; Molding quality; DLP technology 

 

Contact information: a: College of Mechanical Science and Engineering, Northeast Petroleum University, 

Daqing, 163318, China; b: Key Laboratory of Petroleum Mechanical Engineering of Heilongjiang 

Province, Daqing, 163318, China; *Corresponding author: gaosheng_7012@163.com 

 

 
INTRODUCTION 

 

The traditional molding process for lignocellulosic composites typically only 

allows for the manufacture of simple structural wood-plastic parts. In contrast, additive 

manufacturing offers advantages such as simple processes, short cycles, high material 

utilization, and the ability to form complex structures. Additive manufacturing technology 

directly forms materials layer by layer, making it easy to produce parts of lignocellulosic 

composites with intricate internal structures and curved surfaces, thereby enabling more 

complex designs and enhancing the functionality and performance of the parts. 

Additive manufacturing technology shows a diversified trend in the molding of 

lignocellulosic composites, with key techniques including Fused Deposition Modeling 

(FDM), Laminated Object Manufacturing (LOM), and Selective Laser Sintering (SLS). 

Existing studies have utilized various modified composite materials with different 

reinforcement phases. For example, FDM composites were prepared by using modified 

pine wood flour (PWF), a small amount of nano-silica (nano-SiO2), and poly(lactic acid) 



 

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Yu et al. (2025). “Walnut powder DLP 3D printing,” BioResources 20(3), 5348-5360.  5349 

(PLA) (Li et al. 2019); COS/PLA composites were developed by using modified camellia 

seed shells (COS) and PLA (Xiao et al. 2023). The CNF/PLA composite was prepared by 

melt extrusion method of PLA and cellulose nanofibers (CNF) (Wang et al. 2020). 

Boxwood/thermoplastic polyurethane powder (B/TPU) was prepared from poplar waste 

for laser sintering (Zhang et al. 2021). Composite material (WSPC) was prepared from 

walnut shell and copolyester hot melt adhesive (Co-PES) for selective laser sintering (Yu 

et al. 2017). However, in the FDM and SLS molding of lignocellulosic materials, due to 

the characteristics of the technology itself, issues such as uneven distribution and poor 

interfacial bonding are faced, resulting in poor part quality and necessitating additional 

complex post-processing (Wang et al. 2018; Wang et al. 2019). In contrast, Digital Light 

Processing (DLP) technology offers advantages such as smooth surfaces and fast forming 

speeds by curing layer by layer through photopolymerization. It is widely applied in 

automotive, aerospace, medical, jewelry, and other fields. DLP technology uses liquid 

photopolymer resins as printing materials, and researchers are developing composite 

photopolymer resins with different fillers to enhance their comprehensive performance. 

Common fillers include polymer materials, metal particles, fibers, and inorganic 

nanoparticles. 

Lignocellulosic composites are a new type of environmentally friendly, 

biodegradable, and low-cost material made from agricultural and forestry waste combined 

with a polymer matrix (Deng et al. 2018). As the development of natural resources is 

limited, utilizing agricultural and forestry waste, such as walnut shells, to develop new 

composite materials has become a feasible solution. Walnut shells are biodegradable, have 

high hardness, and low density, making them suitable as fillers to improve the performance 

of composites and reduce dependence on traditional wood. 

This paper uses photopolymer resin as the matrix and waste walnut shell powder as 

the reinforcement phase to prepare composites suitable for DLP 3D printing and analyzes 

the impact of different powder contents on the performance of the molded parts. By 

studying the micro-morphological changes in the fracture surfaces of tensile specimens 

with varying walnut shell powder contents, the relationship between the performance of 

the specimens and the powder content is established, and the optimal content ratio is 

determined, providing a reference for the application of walnut shell powder in DLP. 

 

 
EXPERIMENTAL 
 
Materials 
Experimental materials 

The walnut shell powder (approximately spherical particles, particle size range of 

74 to 90 µm, apparent density of 0.56 g/cm³) was obtained from a water treatment materials 

company. Industrial alcohol (a clear liquid with an alcohol content greater than 99% and a 

density of 0.791 g/cm³) was supplied by Harbin Datong Chemical Co., Ltd. (Harbin, 

China). The standard rigid photosensitive resin (main components include polyurethane 

acrylate (PUA), trimethylolpropane triacrylate (TMPTA), modified acrylate, additives, and 

photoinitiators, with a viscosity of 100 to 250 MPa·s at 25 °C) was provided by Shenzhen 

Yidimu Intelligent Technology Co., Ltd (Shen Zhen, China). 

 

  



 

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Yu et al. (2025). “Walnut powder DLP 3D printing,” BioResources 20(3), 5348-5360.  5350 

Composite material preparation 

The composite material was composed of walnut shell powder and a transparent 

photosensitive resin. Walnut shell waste was processed through crushing, screening, 

washing, and filtering to produce porous, yellow-brown particles. The transparent 

photosensitive resin facilitated observation of the mixture’s state. In this study, dried 

walnut shell powder was mixed with the resin at varying mass percentages. To prevent 

powder agglomeration due to high surface energy and static forces, a combination of 

magnetic stirring and ultrasonic dispersion was used: the mixture was magnetically stirred 

for 0.5 h at a temperature below 30 °C, then further dispersed in an ultrasonic cleaner. The 

cavitation effect of ultrasonication breaks up agglomerates, ensuring uniform powder 

distribution. Ultrasonic dispersion also raises the temperature slightly, reducing resin 

viscosity and promoting dispersion. Finally, the mixture was left to stand for degassing and 

was stored in the dark. The proportions of each component are listed in Table 1. 

 

Table 1. The Factors and Levels of Digital Light Processing Test 

Test number I II III IV V VI VII VIII IX X XI 

Percentage by weight of powder (%) 0 2 4 6 8 10 12 14 16 18 20 

Percentage by weight of resin (%) 100 98 96 94 92 90 88 86 84 82 80 

 

 
 

Fig. 1. Preparation process of walnut shell/photosensitive resin composite: (a) preparation 
process of walnut shell powder; (b) composite material mixing process 

 

Methods 
DLP3D printing molding experiment  

The digital light processing (DLP) process for composite parts with different 

ingredient ratios was conducted using a DLP printing device developed by Jiang’s research 

group (Jiang et al. 2022). The equipment and forming process are illustrated in Fig. 2. The 

main process parameters were as follows: light intensity of 50 mW/cm², layer thickness of 

150 µm, single-layer exposure time of 4.5 seconds, base layer exposure time of 38 seconds, 

and processing temperature of 25 ℃. 

Figure 2 illustrates the principle of DLP 3D printing. The forming process involves 

first designing a 3D solid model using 3D software, which is then sliced by a discretization 

program to create a pattern for light exposure. The generated data precisely controls the 

movement of the light source and the lifting platform. Resin is then added to the resin tank, 

where the light source irradiates it, causing photopolymerization within the thin region of 

the resin tank, forming a thin layer of the part. The printing platform then moves up by one 

layer, allowing the light source to continue exposure and process the next layer. This cycle 

repeats, layer by layer, until the complete 3D part is formed. 

 

Photosensitive
resin

Magnetic 
stirring

Ultrasonic
dispersion

Composite
resin

Extract 
shell

remove

Dry

Filter

(a) (b)



 

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Yu et al. (2025). “Walnut powder DLP 3D printing,” BioResources 20(3), 5348-5360.  5351 

 
 

Fig. 2. Equipment diagram and forming process (a) DLP printing equipment; (b) Model slicing 
process; (c) DLP forming process 
 

Viscosity  

The dynamic viscosity of resin systems containing varying proportions of walnut 

shell powder was measured using rotational rheometry with a DV-2 Pro rotary viscometer 

(Brookfield Engineering Laboratories, Inc., USA). A sample volume of 50 mL was tested 

at a temperature of 25°C for each measurement. Three parallel tests were conducted for 

each experimental group, and the arithmetic mean of the results was calculated to 

characterize the rheological properties of the systems. 
 

Double bond conversion rate  

The Nicolet iS20 Fourier-transform infrared (FTIR) spectrometer (Thermo Fisher 

Scientific Ltd, USA), was used to conduct absorbance tests on molded specimens and 

liquid photosensitive resins with varying walnut shell powder content. The tests were 

performed using the Attenuated Total Reflectance (ATR) mode, and the baseline method 

was calculated according to Willard et al. (1988). The C=C stretching vibration peak at 

1638 cm⁻¹ was selected as the target peak, with the NH peak at 1537 cm⁻¹ serving as the 

internal standard for calculating the extent of conversion (Sideridou et al. 2002; 

Papakonstantinou et al. 2013). Due to multiple factors affecting peak shape, this study used 

peak height for calculations. Data analysis was conducted using OMNIC software, with 

automatic baseline correction and peak height measurement using the two-point baseline 

method. The final double bond conversion rate was calculated by Eq. 1 (Hong et al. 2017), 

𝐷𝐶 = (1 −
HB1/HB2

HA1/HA2
) × 100%                                               (1) 

where DC represents the Double Bond Conversion percentage (%), HB1 denotes the peak 

height of the target after curing, and HB2 indicates the peak height of the internal standard 

after curing. HA1 represents the peak height of the target before curing, HA2 is the peak 

height of the internal standard before curing. 

 

 

 

 

Lens

Light 

source

UV-light

Composite 

resin

Forming 

platform

Forming 

direction

Sample piece

Three-dimensional model Model slice

Slicing 

program

h

h：thickness（a） （b）

（c）



 

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Yu et al. (2025). “Walnut powder DLP 3D printing,” BioResources 20(3), 5348-5360.  5352 

Mechanical properties 

The mechanical properties of composite parts with different component ratios were 

tested using the CMT 5504 tensile testing machine from TMS System Ltd. and the TCJ-4 

impact testing machine from Jilin Taihe Co., Ltd. (Changchun, China). The tensile strength 

was measured according to ISO 527-2 standards. The crosshead speed was set at 5 mm/min 

with a gauge length of 50 mm. The dimensions of the tensile specimen, shown in Fig. 3(a), 

were 80 mm × 5 mm × 4 mm. The three-point bending strength was measured according 

to ISO 178 standards. The crosshead speed was also set at 5 mm/min, with a span length 

of 64 mm. The dimensions of the bending specimen, illustrated in Fig. 3(b), were 80 mm 

× 10 mm × 4 mm. The U-notch impact strength was measured according to ISO 179-2 

standards. The pendulum impact energy was set to 4 J, with a span length of 60 mm. The 

dimensions of the impact specimen, shown in Fig. 3(c), were 75 mm × 10 mm × 3 mm. 

 

 
 

Fig. 3. Test sample model diagram; (a) tensile specimens; (b) Bending specimens; (c) Impact test 
pieces; (d) Dimensional shrinkage test specimen 

 

Dimensional shrinkage 

As shown in Fig. 3(d), the length (X), width (Y), and height (Z) of the sample were 

measured five times using a digital caliper, and the average values were taken. The 

theoretical dimensions of the sample are 1 cm × 1 cm × 1 cm. The dimensional shrinkage 

(%) was calculated using Eq. 2 (Xu et al. 2021), 

𝐿 =（
|𝑋−𝑋0|

3𝑋0
+

|𝑌−𝑌0|

3𝑌0
+

|𝑍−𝑍0|

3𝑍0
) × 100%                      (2) 

where L denotes the percent shrinkage, X0, Y0, and Z0 represent the theoretical dimensions 

of the sample, and X, Y, and Z are the actual dimensions of the sample. 

 

Scanning electronic microscopy (SEM)  

Since the samples were initially non-conductive, they were gold-coated for 45 

seconds using a Quorum SC7620 sputter coater at a current of 10 mA prior to testing. The 

cross-sections of composite powders and formed components with different composition 

ratios were scanned using a ZEISS GeminiSEM 300 (Germany) scanning electron 

microscope. The instrument employs a Schottky field emission electron gun with an 

acceleration voltage of 3 kV. SEM images were obtained to characterize the powder 

particle morphology and internal microstructure of composite material components with 

varying composition ratios. 



 

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Yu et al. (2025). “Walnut powder DLP 3D printing,” BioResources 20(3), 5348-5360.  5353 

Density 

Using the DMA 4200M density analyzer (Anton Paar GmbH, Austria) based on 

Archimedes’ principle—gas expansion displacement method, density measurements were 

conducted on composite material molded parts containing varying proportions of walnut 

shell powder. Cubic specimens with dimensions of 10 mm × 10 mm × 10 mm were 

prepared. Three parallel measurements were performed for each sample group, and the 

arithmetic mean of the results was adopted as the density characterization parameter. 

 

 

RESULTS AND DISCUSSION 
 
Double Bond Conversion Rate  

The infrared spectra of samples with different walnut shell powder contents 

before and after forming are shown in Fig. 4. 
 

 
 
 

Fig. 4. Infrared spectra of walnut shell/photosensitive resin molded parts with varying ratios; (a) 
Infrared spectrum before forming; (b) Infrared spectrum after forming 

 

The double bond conversion data for formed components with varying powder 

contents are summarized in Table 2. The extents of conversion demonstrated a significant 

decreasing trend with increasing walnut shell powder content, declining from 53.5% at 0% 

powder content to 23.6% at 20% powder content. This reduction primarily stems from UV 

light scattering by walnut shell particles during photopolymerization, which attenuated 

light penetration depth into the resin matrix and consequently diminished both irradiance 

intensity and conversion efficiency (Niu et al. 2020). 

 

Table 2. Double Bond Conversion of Molded Parts with Different Powder Content 
of Walnut Shell 

Powder Content Peak Corrected Height Baseline DC 

Uncured Resin 
1537 0.0514 1492.634,1569.290 

/ 
1638 0.0952 1571.219,1655.589 

0% 
1537 0.0748 1489.741,1581.825 

53.5% 
1638 0.0644 1587.128,1664.749 

2% 
1537 0.0859 1488.777,1572.665 

48.2% 
1638 0.0824 1574.111,1665.231 

4% 1537 0.0799 1487.813,1568.326 42.3% 

 

A
b

s
o

rb
a
n

c
e

0.00

0.05

0.10

0.15

0.20

0.30

1400 1500 1600 1700

1638cm
-1

1537cm
-1

0% 2% 4%

6%

12%

8% 10%

14% 16%

18% 20%

(a)

0.25

Wavenumber(cm
-1

)

 

0.00

0.05

0.10

0.15

0.20

0.25

0.30

1638cm
-1

1537cm
-1

0% 2% 4%

6%

12%

8% 10%

14% 16%

18% 20%
A

b
s
o

rb
a
n

c
e

(b)

1400 1500 1600 1700
Wavenumber(cm

-1
)



 

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Yu et al. (2025). “Walnut powder DLP 3D printing,” BioResources 20(3), 5348-5360.  5354 

Powder Content Peak Corrected Height Baseline DC 

1638 0.0855 1571.701,1663.785 

6% 
1537 0.0779 1489.259,1568.808 

40.4% 
1638 0.0861 1572.665,1664.749 

8% 
1537 0.0802 1490.705,1580.379 

39.6% 
1638 0.0897 1584.236,1665.231 

10% 
1537 0.0768 1491.187,1569.772 

38.8% 
1638 0.0871 1571.701,1664.267 

12% 
1537 0.0717 1491.669,1577.486 

37.0% 
1638 0.0802 1579.896,1667.642 

14% 
1537 0.0734 1488.295,1569.772 

29.9% 
1638 0.0953 1573.629,1665.714 

16% 
1537 0.0577 1492.634,1572.183 

24.1% 
1638 0.0811 1573.629,1665.231 

18% 
1537 0.0702 1490.223,1566.880 

24.0% 
1638 0.0989 1572.665,1668.124 

20% 
1537 0.0702 1488.295,1570.737 

23.6% 
1638 0.0993 1573.629,1665.231 

 

 

Viscosity  
As shown in Fig. 5, the viscosity of the walnut shell/photosensitive resin composite 

system exhibited a significant upward trend with increasing walnut shell powder content, 

rising from 255 cP at 0% powder content to 510 cP at 20% powder content. Excessive 

viscosity impeded resin layer recoating, increasing the likelihood of air bubble entrapment 

and resulting in the formation of internal pores after curing. Additionally, heightened 

adhesion forces amplified demolding effects during the forming process, inducing defects 

such as warpage deformation, which ultimately degraded the structural integrity of the 

molded parts. Therefore, precise control of walnut shell powder content in the resin system 

is essential to mitigate these processing challenges and ensure optimal performance of the 

final product. 

 

Viscosity

V
is

c
o

s
it

y
 (

c
P

)

250

300

350

400

450

500

550

0 2 4 6 8 10 12 14 16 18 20

Walnut shell powder content (%)  
 

Fig. 5. Viscosity profile of walnut shell/photosensitive resin molded parts with varying ratios 
 
DLP 3D Printing Experiment  

Figure 6 shows that as the walnut shell powder content increased, part deformation 

decreased. When the walnut shell powder content exceeded 2%, warping was reduced 



 

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Yu et al. (2025). “Walnut powder DLP 3D printing,” BioResources 20(3), 5348-5360.  5355 

because the walnut shell powder does not participate in the molding reaction or deform, so 

increasing its content can reduce strain in the molded part. However, at a powder content 

of 16%, Fig. 6(c) showed significant deformation of the molded part. Higher powder 

content reduces dispersion uniformity and the resin’s light transmittance, affecting the 

curing depth and leading to uneven UV absorption, which creates internal stress and 

deformation. Additionally, hollows formed by powder agglomeration further exacerbate 

deformation. Therefore, the walnut shell powder content should not be excessively high. 

 

 
Fig. 6. (a) Tensile parts with different component ratios; (b) defects on the left side; (c) defects on 
the right side 

 

Mechanical Properties  
Figure 7 shows the variation in mechanical properties of molded parts with different 

walnut shell/resin ratios. As the walnut shell powder content increased, the impact strength 

of the molded parts decreased, while the tensile and bending strength initially increased 

and then decreased. When the powder content was below 8%, the tensile and bending 

strength improved. This is because, after resin curing, a honeycomb-like structure formed 

on the surface of the powder particles, enhancing the interfacial bonding strength between 

the walnut shell powder particles and the resin, thereby improving the mechanical 

properties (Li et al. 2022). Additionally, the powder particles inhibited the propagation of 

internal cracks in the resin during fracture, further enhancing resistance to external forces. 

When the powder content reached 8%, the tensile and bending strengths reached their 

maximum values of 17.7 and 45.4 MPa, respectively. When the powder content exceeded 

8%, the mechanical properties decreased due to agglomeration that forms cavities, reducing 

the degree of curing. Figure 7(c) shows that the impact strength declined rapidly before the 

powder content reached 8% and stabilized. This is because the nearly spherical powder 

particles do not enhance the part’s resistance to short-term external impacts. 

 



 

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Tensile 
strength

8

10

12

14

16

18
T

e
n

s
il

e
 s

tr
e
n

g
th

 (
M

P
a

)

(a)

0 2 4 6 8 10 1412 16 18 20

Walnut shell powder content (%)

Bending 
strength

0

Walnut shell powder content (%)

2 4 6 8 10 1416 18 2012 14

48

44

40

36

32

28

24

B
e
n

d
in

g
 s

tr
e
n

g
th

 (
M

P
a
) 

(b)

Impact 
strength

2 4 6 8 10 12 14 16 18 200

Walnut shell powder content (%)

9

8

7

6

5

4

10

Im
p

a
c

t 
s
tr

e
n

g
th

 (
M

P
a

)

(c)

 
 

Fig. 7. Mechanical properties of walnut shell/photosensitive resin molded parts with varying 
ratios: (a) tensile strength; (b) bending strength; (c) impact strength 
 

Dimensional Shrinkage Rate  
During the photocuring process, the monomers, oligomers, and photoinitiators in 

the photosensitive resin absorb ultraviolet light, transitioning from a liquid to a solid state. 

This causes curing shrinkage in the molded part, making its actual dimensions smaller than 

the theoretical ones. Figure 8 shows that when the walnut shell powder content was below 

12%, the shrinkage rate of the molded part gradually decreased, and overall accuracy 

improved. This is because the walnut shell powder particles do not undergo chemical 

reactions or deformation during curing, reducing changes in molecular distances within the 

resin due to changes in chemical bonds. At a powder content of 12%, the shrinkage rate 

reached a minimum of 0.631%. When the powder content exceeded 12%, the powder was 

prone to agglomeration, forming hollows and reducing the resin's light transmittance. This 

prevents UV light from being uniformly distributed, leading to over-curing or cavity 

formation, which decreases molding accuracy. 

 

2 4 6 8 10 12 14 16 18 200

Walnut shell powder content (%)

0.5

2.5

2.0

1.5

1.0

DS

D
im

e
n

s
io

n
a
l 
s

h
ri

n
k
a

g
e
 (

%
)

 
 

Fig. 8. Dimensional shrinkage of walnut shell/photosensitive resin molded parts with varying 
ratios 
 

Scanning Electronic Microscopy 
The SEM observation of the tensile fracture surfaces reveals that the fracture 

surfaces in Fig. 9(a-c) were relatively smooth, with no noticeable fibrillation or 

deformation, indicating brittle fracture characteristics. In Fig. 9(a), the molded specimen 

with 8% powder content shows uniformly distributed walnut shell particles, tight 



 

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Yu et al. (2025). “Walnut powder DLP 3D printing,” BioResources 20(3), 5348-5360.  5357 

interfacial bonding, and no agglomeration. In Fig. 9(b), at 12% powder content, the 

uniformity of particle distribution decreased, with agglomeration and hollows forming. In 

Fig. 9(c), the powder content of 18% showed reduced uniformity, with significant 

agglomeration.  

Figure 9(d) demonstrates that the porous surfaces of walnut shell particles were 

infiltrated by liquid photosensitive resin, which then cured to form a honeycomb structure. 

This structure enhances interfacial bonding strength and improves mechanical properties. 

Fig. 9(e) shows that as walnut shell powder content increases, material transparency 

decreases, leading to uneven UV absorption by the photosensitive resin. This results in 

tighter bonding on the side facing the UV light, causing over-curing, while the side 

opposite the light source may have cavities due to insufficient UV absorption. 

 

 

 

 
 

Fig. 9. Cross section scanning electron microscopy (SEM) images of walnut shell/photosensitive 
resin forming parts with different composition ratios: (a) 8% walnut shell powder content, 
magnified 200 times; (b) 12% walnut shell powder content, magnified 400 times; (c) 18% walnut 
shell powder content, magnified 400 times; (d) 12% walnut shell powder content, magnified 600 
times; (e) 18% walnut shell powder content, magnified 1,000 times; (f) 18% walnut shell powder 
content, magnified 400 times 

 （a）

Walnut Shell Powder

100μm

 

50μm

Hollow

（b）

 

Hollow

Cavity

50μm

（c）  

Network Structure

50μm

（d）

 

Cavity

（e）

20μm

 
Agglomeration

（f）

50μm



 

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Density  
The density variation of walnut shell/photosensitive resin molded parts with 

different ratios is shown in Fig. 10. As illustrated, the density of the molded parts decreased 

consistently with the increase in walnut shell powder content, with the rate of decrease 

gradually accelerating. This trend occurred because the density of walnut shell powder was 

lower than that of the photosensitive resin, and its addition reduced the overall density of 

the molded part. Additionally, as the powder content increased, distribution uniformity 

decreased, leading to an increase in hollows and cavities during the molding process, which 

further accelerated the reduction in density. 

 

Density

0 2 4 6 8 10 12 14 16 18 20

1.12

1.24

1.22

1.20

1.18

1.16

1.14D
e
n

s
it

y
 (

g
/c

m
3
)

Walnut shell powder content (%)  
 

Fig. 10. Density bar chart of walnut shell/photosensitive resin molded parts with varying ratios 
 
 

CONCLUSIONS 
 

1. The cured dimensions were larger than the theoretical ones. Shrinkage minimized 

(0.631%) at a walnut shell content of 12%, while density decreased with higher walnut 

shell content. 

2. The extent of double bond conversion demonstrated a sharp decrease with increasing 

walnut shell powder content, plummeting from 53.5% at 0% powder content to 23.6% 

when the powder concentration reached 20%. 

3. Brittle fracturing revealed surface-proximate cross-sectional structures of the 

composite. Imaging showed a developed honeycomb structure near the surface, 

enhancing resin-particle binding tightness. However, increased walnut content 

promoted agglomeration, forming strength-reducing cavities and hollows. 

4. Impact strength decreased as powder content rose, while tensile and flexural strengths 

peaked at 8% walnut shell content (17.7 and 45.4 MPa). 

 

 

  



 

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ACKNOWLEDGMENTS 
 

This work was supported by the Guided Innovation Fund project of Northeast 

Petroleum University(2022YDL-06）, National Cultivation Fund Project of Northeast 

Petroleum University(2024GPL-10), the Joint Scientific and Technological Innovation 

Project of Hainan Province(2021CXLH0001), Key R&D Program of Heilongjiang 

Province, China (JD2023SJ23), General Research Project of Higher Education Reform in 

Heilongjiang Province (SJGYY2024186), the Scientific Research Start-up Fund Project of 

Northeast Petroleum University (2021KQ09 and 2019KQ67). 
 
 
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PEER-REVIEWED ARTICLE bioresources.cnr.ncsu.edu 

 

 

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Article submitted: November 10, 2024; Peer review completed: April 2, 2025; Revisions 

accepted: April 7, 2025; Published: May 9, 2025. 

DOI: 10.15376/biores.20.3.5348-5360