Page 56 - 《橡塑技术与装备》英文版2025年12月

HINA R&P TECHNOLOGY AND EQUIPMENT

(approximately 0.2 g) was extracted in boiling acetone for 12 V f (1−S f )
12 2
1− =1− (4)
12 2
hours, then dried to constant weight in an oven at 80°C, and V i (1−S i )
S i represents the sol content of untreated rubber powder;
the weight m1 was measured. The sample was immersed in
toluene at room temperature for 72 hours to achieve diffusion S f represents the sol content of desulfurized rubber powder; V i
represents the crosslinking density of untreated rubber powder;
equilibrium of swelling. Subsequently, the sample was taken
V f represents the crosslinking density of desulfurized rubber
out, and the solvent was quickly removed using filter paper.
powder.
Then, the swelling weight was immediately measured, denoted
In addition, in the case of pure crosslink fracture, the
as m 2 . Finally, the sample was dried to constant weight in an
soluble fraction is related to the relative decrease in crosslink
oven at 80°C, and the weight was measured in units of m 3 . The
density, as shown below:
crosslinking density (equation (2)) is defined as:
1/2 2
2 V f γ f (1−S f )
ln(1−V r )+V r +xV r 1− =1− (5)
1/2 2
V e = (2) V i γ i (1−S i )
1/3
V s (0.5V r −V r ) Where γ f and γ i represent the average number of
Where Ve represents the crosslinking density; Vr denotes
crosslinks per chain in the insoluble network after and before
the volume fraction of the polymer in the swollen sample;
desulfurization, respectively (f denotes final, and i denotes
V stands for the Flory-Huggins polymer-solvent interaction
parameter; and Vd signifies the molar volume of the solvent, initial). γ i and γ f are the average number of crosslink sites per
chain in the insoluble network before and after desulfurization,
-1
which is 106.3 mL·mol . The primary rubber component of
which can be determined by the method described by
CR is natural rubber, and the corresponding Flory-Huggins
Verbruggen.
polymer-solvent interaction parameter, x, for the natural
(5) SEM
rubber-toluene system is 0.393.
Scanning Electron Microscopy (SEM, ZEISS
(3) Calculation of desulfurization degree
GEMINISEM 360, Carl ZEISS AG, Germany) was utilized
The desulfurization rate is calculated according to the
formula specified in ASTM D6814-02 standard as follows: to analyze the micromorphology of CR and SCR. Prior to
testing, CR and SCR were adhered to a conductive adhesive.
Rd=(V e1 -V e2 )/V e1 (3)
To obtain the conductivity of the samples, Oxford Quorum
Among them, V e1 and V e2 represent the crosslinking
density of the rubber powder before and after desulfurization, SC7620 gold spraying equipment was employed to perform 10
mA gold spraying. CR and DCR, which possess conductivity,
respectively.
were placed in the sample chamber of the SEM and
(4) Horikx curve
underwent a vacuum pumping step. Once a testable vacuum
Changes in sol fraction and crosslinking density are
level was achieved, vacuum pumping was ceased, and the
influenced by the breakage of main chains and crosslinks
micromorphology of CR and DCR samples was captured. The
during degradation. To investigate the process of bond
accelerating voltage was set at 3 kV, and images were captured
breakage, a theoretical relationship between sol fraction and
crosslinking density was established using Horikx theory . Horikx at a magnification of 2,000 times.
theory consists of two aspects: the relationship between 1.3.2 Testing of PMA
According to the relevant test methods outlined in the Test
crosslinking density and sol fraction can only be explained
Methods of Bitumen and Bituminous Mixtures for Highway
by equation (4) when main chain breakage occurs; the
relationship between crosslinking density and sol fraction Engineering (JTG E20-2011), the physical properties of modified
asphalt are measured, including softening point, needle penetration at
can only be explained by equation (5) when crosslink bond
25℃ , ductility at 5℃ , and elastic recovery at 25℃ .
breakage occurs. Based on equations (4) and (5), and the data
on sol fraction and crosslinking density tested in experiments,
the Horikx curve can be determined and used to analyze the 2 Results and Discussion
2.1 Analysis of Horikx curve of DCR
method of bond breakage.

·50· Vol.51，No.12