Core-sheath Electrospinning of Shea Butter and Cellulose Acetate to Enhance Heat Transfer in Protective Clothing

doi:10.21203/rs.3.rs-978565/v1

Protective clothing for health workers requires heat transfer in hot and humid environments. To study the thermal conduction of phase-change materials and protect them from leakage, we selected skin-friendly shea-butter due to its suitable melting temperature, and the electrospinning processibility of biocompatible cellulose acetate. The shea-butter as a phase-change material was encapsulated in electrospun cellulose acetate fibres within a core/sheath structure, which was stabilised by two concentric Taylor cones during coaxial electrospinning. Transmission and scanning electron microscopy revealed a blood-in-tube vessel-like morphology. Next, differential scanning calorimetry and thermogravimetric analyses confirmed the heat capacity of shea-butter (latent heat of fusion: 42.73 J/g; thermal conductivity: 1.407 W/m∙K). The flow rate of the core was proportional to the heat capacity of the shea-butter/cellulose acetate fibres. This was consistent with the finding that the electrospun fibres of the highest-ratio shea-butter (16.19%) had the highest thermal conductivity (0.421 J/g∙K). The shea-butter:cellulose acetate ratio was approximately 15:80. The efficacy of heat transfer for the core/sheath fibres in human clothing was assessed by measuring skin temperatures at 13 sites in six males aged 25 to 35 under two conditions: wearing a mask and hood with attached cellulose acetate fibres in the presence and absence of shea-butter. The mean difference in skin temperatures (0.5 ℃) between the two conditions was significant. Coaxial electrospinning of shea-butter/cellulose acetate fibres is therefore promising for protective clothing with efficient heat-transfer in the use of a large area.

General Cell Biology & Physiology

electrospinning

cellulose acetate

phase change material

heat transfer

skin temperature

protective clothing

Table 1 Various literature of electrospinning cellulose acetate with multifunctional additives

Materials

Process parameters

Results of enhancement

Ref.

- CA DA¹ 39.8%

- Mn=30 kDa

- sheath : CA

- core : oil, chitosan, PCL²

- Sheath: 12~17 wt% CA

- Core: 1~20 wt%

- acetone:dioxene 2:1 (14% CA)

- 5~20 kV, 5~12 cm

- tensile strength of PCL-CA (wet states)

- vascular endothelial cells attachment

- hydrophilicity of CA (wet states)

- hydrophobicity of PCL (wet states)

Khalf et al., 2015

- CA DA 39.7%

- Mw=50,000

- 15 wt% CA

- DMF:acetone 2:3

- 0.05/0.5/1.0/1.5 wt% GO³

- 0.13 mL/h, 27 kV, 15 cm

- tensile strength in the presence of GO by 73% than in the absence of GO.

Aboamera et al., 2019

- CA DA 38~40 %

- 9 wt% CA

- 0.05/0.10/0.15 mol/L TBAC⁴

- 1.0 ml/h, 30~40 kV, 15 cm

- deacetylation in sodium hydroxide

- hydrophilicity, mechanical properties, chemical resistance by adding TBAC

- filter efficiency (98.37%)

Zhang et al., 2018

- CA/CNT/Ag₃

- 17 wt% CA

- DMF:acetone 1:2

- 3%/5%/8% CA/CNT/Ag

- 15 kV, 15 cm

- fiber diameter: 316~587 nm.

- 100% bactericidal action (cellular viability 0%).

Jatoi et al., 2020

- CA DA 39.8%

- Mw = 30,000 g/mol

- 20% CA

- acetone:DMF: 2:3 (wt%)

-1 ml/h, 18 cm, 15 kV

- deacetylation of electrospun CA

- antibiotic nanoparticles

: silver for E.coli bacillus

: copper for B. subtilis bacillus

Phan et al., 2019

- CA

- Mw = 25,000

- 8 wt%/0.8 wt%/0.8 wt% CA/TiO₂/GO sheet

- DMF:acetone 1:2

- 0.75 ml/h, 20 kV, 20 cm

- Synergistic effects

- antibiosis against Bacillus subtilis

- antibiosis against Hay bacillus.

Jia et al., 2019

- CA DA 39.7%

- Mn = ~100,000 Da

- 9%, 12%, 15% CA/acetone (w/v)

- 2 ml/h, 8~16 kV, 6~14 cm.

- optimal fiber formation

- 12%~15% CA (w/v): few beads

- 15% CA (w/v): no beads yet ununiform diameter (404~1346 nm)

Angel et al., 2020

^{1 DA: Acetylation degree, 2 PCL: Polycaprolact-one, 3 GO: graphene oxide, 4 TBAC: tetra butyl ammonium chloride}

Table 2 Component contents of fatty acids and each melting-boiling point of the components

Fatty acids	Lauric acid (C₁₂H₂₄O₂)	Myristic acid (C₁₄H₂₈O₂)	Palmitic acid (C₁₆H₃₂O₂)	Linoleic acid (C₁₈H₃₂O₂)	Oleic acid (C₁₈H₃₄O₂)	Stearic acid (C₁₈H₃₆O₂)
ShB	*	*	3.3~3.9	6.1~6.3	45.7~46.5	41.8
CCN¹	52.0~53.2	16.8~21.0	7.5~10.2	*	5.0~10.0	2.0~4.0
Melting point (℃)²	44.0	53.5	59.8	-13.0	-5.7	67.6
Maximum (℃)³	*	55.5	63.9	-4.1	15.2	70.0
Boiling point (℃)	298.9	326.2	351.0	230.0	223.0	386.0

¹^{Floros & Narine 2016,}²^{Leakey 1999,}³^Lawer-Yolar^{et al}^.²⁰¹⁹

Table 3 Specifications of PCM-CA electrospun fibers

No	Code	PCM	Concent. (wt%)	Solvent	Additives	Flow rate (㎖/h)
No	Code	PCM	Concent. (wt%)	Solvent	Additives	Core	Sheath
1	A-1T	ShB	15.0	A:DMF 1:1	TiO₂, ZnO	1.0	2.0
2	A-1	ShB	15.0	A:DMF 1:1	*	1.0	2.0
3	A-2T	ShB	15.0	A:DMF 1:1	TiO₂, ZnO	1.0	4.0
4	A-2	ShB	15.0	A:DMF 1:1	*	1.0	4.0
5	B-1T	ShB	17.5	A:DMF 1:1	TiO₂, ZnO	1.0	4.0
6	B-2T	ShB	17.5	A:DMF 1:1	TiO₂, ZnO	0.5	4.0
7	B-3T	ShB	17.5	A:DMF 1:1	TiO₂, ZnO	0.5	3.0
8	B-4T	ShB	17.5	A:DMF 1:1	TiO₂, ZnO	1.0	3.0
9	C-1	ShB	22.5	A:DMF 1:1	*	1.0	4.0
10	C-2	ShB	22.5	A:DMF 1:1	*	0.5	4.0
11	D-1	ShB	25.0	A:DMF 1:4	*	0.5	4.0~6.5
12	CCN-D-14	CCN	25.0	A:DMF 1:4	*	0.9	4.5
13	C/S-D-14	C/S	25.0	A:DMF 1:4	*	0.9~1.0	4.5~4.6
14	C/S-D-41	C/S	25.0	A:DMF 4:1	*	1.0	4.0

Table 4 DSC results of PCM-CA fibers corresponding to concentration of CA and injection rate of core-sheath

Specimen		ShB	CCN	A-1T	A-2T	B-1T	B-2T	B-3T	B-4T	C-1
Concent.	(wt%)	*	*	15	15	17.5	17.5	17.5	17.5	22.5
Flow rate (ml/h)	Core	*	*	1.0	1.0	1.0	0.5	0.5	1.0	1.0
Flow rate (ml/h)	Shell	*	*	2.0	4.0	4.0	4.0	3.0	3.0	4.0
T_onset (℃)	1st heat, T_m	32.06	25.70	27.15	27.28	27.37	27.42	27.44	27.23	28.32
	1st cool, T_c	13.49	4.54	12.16	12.53	13.00	13.85	12.70	12.35	12.85
	2nd heat, T_m	2.65	*	2.42	0.52	1.63	1.93	2.61	2.93	7.58
T_peak (℃)	1st heat, T_m	37.86	30.27	33.61	36.67	37.19	35.98	35.52	36.27	34.59
	1st cool, T_c	8.79	2.13	6.33	6.86	6.68	7.89	6.84	6.65	8.28
	2nd heat, T_m	13.80	*	13.27	13.08	13.89	13.85	13.52	13.35	13.82
Enthalpy, (J/g)		42.73	20.13	15.91	7.365	9.48	5.26	12.17	17.04	2.505
Specific heat, C_p (J/g·K^-1)		1.899	0.895	0.707	0.327	0.421	0.234	0.541	0.757	0.111
Energy transfer (W/g)		0.317	0.149	0.118	0.055	0.07	0.039	0.09	0.126	0.019
Thermal conductivity, k (W∙m^-1∙K^-1)		1.407	*	0.524	0.242	0.312	0.173	0.401	0.561	0.082

Table 5 TGA results of degradation temperature and mass ratio for PCM-CA fibers corresponding to components of fatty acids

Speci-men	Onset Tempe-rature (℃)	DTG peak (℃)	End Tempe-rature (℃)	Mass ratio (%)
				Volatilization	Thermally degradation		Residue
				~300 ℃	300~400 ℃	400~500 ℃	500~℃
				C18:1, C18:2	CA / C16:0	C18:0	Others
ShB	423.97	461.14	477.35	2.36	- / 3.60 [ref]	89.81[calculated]	2.33
A-2	345.03	371.05	396.62	6.58	78.56 / -	15.02	-
B-1T	337.90	369.81	395.08	6.76	77.48 / -	16.19	-
B-2T	344.97	369.43	391.12	5.77	78.93 / -	15.47	-
C-1	348.28	372.43	389.66	6.59	78.99 / -	14.61	-
C-2	341.10	369.30	387.59	7.05	80.04 / -	13.19	-
CA	354.07	378.54	389.61	6.16	72.66 / -	-	21.33

Table 6 Paired differences in mean skin temperatures of subjects between wearing hoods with PCM-CA fibers and hoods without PCM in CA fibers

Subject		Paired differences (℃)				t-value	DF	Sig.
		PCM	No PCM	Mean difference	Standard deviation
		PCM	No PCM	Mean difference	Standard deviation
A	Pair 1	34.899	33.883	1.009	1.372	22.137	905	.000^***
B	Pair 2	34.157	34.650	-0.554	0.934	-17.863	905	.000^***
C	Pair 3	34.997	30.013	5.041	1.557	97.460	905	.000^***
D	Pair 4	35.688	35.088	0.597	0.248	72.357	905	.000^***
E	Pair 5	35.540	35.409	0.135	0.282	14.435	905	.000^***
F	Pair 6	34.954	34.757	0.188	0.322	17.556	905	.000^***

^*^{p<.05, **p<.01}^{, ***p<.001}

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Core-sheath Electrospinning of Shea Butter and Cellulose Acetate to Enhance Heat Transfer in Protective Clothing

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