Indian Journal of Fibre & Textile Research Vol. 29, March 2004, pp. 7-11

A new photothermal conversion and thermo-regulated fibresa

Hni Feng Shib, Xing Xiang Zhang, Xue Chen Wang & lian lin Niu

Institute of Functional Fibre, Tianjin Polytechnic University, Tianjin, 300160, China

Received 10 July 2002; revised received and accepted 20 January 2003

Photothermal conversion and thermo-regulated fibres (PCTFs) have been prepared using the fibre-forming polymer containing photothermal conversion ceramic as sheath and the fibre-forming polymer containing microPCMs as core. The structures and properties of the PCT fibres, such as mechanical property, photothermal conversion ability, and temperature­regulating ability, have been studied using DSC, IR lamp, temperature sensors and SEM. It is observed that the photothermal conversion and thermo-regulated fibres have better photothermal conversion and temperature-regulating abilities when compared with the control. The maximum heat absorbing and heat releasing temperature differences are found to be 4.5°C and 6.5°C respectively when the PCTF nonwoven is compared with PP nonwoven.

Keywords: Microencapsulated phase change material , Photothermal conversion ceramic, Polypropylene, Thermo-regulated fibre

IPC Code: Int. CI.7 DOIF 1110, DOlO 11100

1 Introduction The technology for applying phase change material

(PCM) to textile fibres or fabrics to improve their thermal performance was developed in 1980s under the NASA research project'. The PCM possesses the ability to store and release a large amount of latent heat when they go through solid-liquid transitions. By selecting the materials that change phase around skin temperature, the textiles containing PCM can create a thermo-regulating effect, responding to temperature changes between the human body and the outside environment. Therefore, the study of heat-storage and thermo-regulated textiles has attracted more and more attention in recent years2

,3. The wet-spun polyacrlonitrile (PAN) fibre that contains microPCMs has been developed during 1997 (ref.4). However, the content of microPCMs in the wet-spun PAN fibre was only 6-7% (W/w)5. Later, the polypropylene (PP) and poly(butylene terephthalate)(PBT) fibres containing 3%(w/w) microPCMs were melt-spun in laboratorl. However, the 3%(w/w) amount of microPCMs was too low to push the fibre into the market. The study on the use of photothermal conversion ceramic as sheath and the microencapsulated phase change

"Presented in part at the First International Avantex Symposium, May 2002, Frankfurt, German ~o whom all the correspondence should be addressed. Present address: State Key Laboratory of Polymer Physics & Chemistry, Institute of Chcmistry, Chinese Academy of Sciences, Beijing, China. Phone: +86-10-24528282; E-mail : shihf@pplas.icas.ac.cn

material as core for manufacturing heat storage and thermo-regulated composite fibres has not been reported so far. The effect of microPCMs content on the properties of heat-storage and thermo-regulated fibres has also not been reported. The present work was, therefore, aimed at preparing the photothermal conversion and thermo-regulated fibres (PCTFs) using fibre-forming polymer containing photothermal conversion ceramic as sheath and the fibre-forming polymer containing microPCMs as core. The properties, such as mechanical property, latent heat , heat storage, temperature regulation ability and photothermal conversion ability, of the fibre and the nonwoven made out of it have also been studied.

2 Materials and Methods

2.1 Materials

2.1.1 Chips

The phase change material was selected from the hydrocarbons with predetermined melting and crystallizing temperatures (Table 1). In this work, octadecane was selected as phase change material. The microcapsules containing the phase change materials were synthesized using certain thermoplastic resin as container by ill-situ polymerization in the laboratory and the diameter range of microcapsule was between 111m and IOllm. The microPCMs powders and polyethylene were mixed, melt extruded into water, cut into the chips

8 INDIAN 1. FIBRE TEXT. RES., MARCH 2004

Table I-Properties of phase change materials used

Phase change Crystalli zati on point Melting point material °C °C

Octadecane 25.4 28 .2

Heptadecane 2 1.5 22.5

Hexadecane 16.2 18.5

and then used as core components. The 4% (w/w) of photothermal conversion ceramic (ZrC) and the polypropylene were melt extruded into water, cut into the chips and then used as sheath components7

.

2. 1.2 Fibre The polyethylene polymer containing

microencapsulated phase change material was used as core component and the polypropylene containing 4% (w/w) photothermal conversion ceramic was used as sheath component. In a weight ratio of 6/4 (core/sheath), the photothermal conversion and thermo-regulated sheath/core composi te fibres (PCTFs) were melt spun. The PCT fibres were curled, cut and then used for manufacturing nonwoven (weight, 400g/m2

). For the study, three different samples of PCTFs, namely HTl, HT2 and HT3, having 6%, 9% and 12% of PCMs respectively were prepared.

2.2 Methods

2.2. J SEM Study Scanning electron photomicrographs of PCTFs

were taken by KYKY -2800 (20kV) instrument produced by Beijing Zhongke Keyi Technology Development Ltd. The specimens were coated with silver in ion sputtering device under vacuum for 5 min.

2.2.2 Differential Scanning Calorimeteric (DSC) Analysis DSC analysis was conducted using a Perkin-Elmer

DSC-7 instrument. The 6-8 mg specimen was put in aluminum holder. Thermographs for both PCTF powders (HTl, HT2 and HT3) and chips (samples S(, S2 and S3) were recorded under the protection of ultra pure dry nitrogen. The temperature of rising and cooling rate was 10'tlmin.

2.2.3 Measurement of Temperature Regulation Ability To test the temperature regulation ability of the

PCTF nonwoven, the microencapsulated phase'" change material must change from liquid to solid and vice versa8

. The effect can be studied when fabrics go

l:hrough a temperature change. Therefore, the tes t was conducted in both warm and cold conditions. The inner temperature of PCTF nonwoven and polypropylene nonwoven was measured using thermographs when the atmospheric temperature changes from O°C to 50°C and from SO°C to O°C. The inner temperature of sample and the measurement ti me recorded are given below:

Ts Tp

-inner temperature of PCTF sample -inner temperature of PP sample

(control) LlTd (Ts-Tp) -maximum difference in temperature

of PCTF and PP nonwoven during temperature rising process.

LlTg (Ts-Tp) -maximum difference in temperature of PCTF and PP nonwoven during temperature decreasing process.

2.2.4 Measurement of Photothermal Conversion Ability

It was reported that the carbides of IV group metals have the ability of absorbing the energy of wavelength less than 2 11m and thoroughly reflecting the ray of wavelength longer than 211m in the solar radiation spectrum9

. To test this photothermal conversion ability, the experiment was conducted under IR lamp (250W, 1-2.5 11m spectrum) irradiation. The test results of the PCTF nonwoven and the polypropylene nonwoven were recorded after every 2 min and compared.

3 Results and Discussion

3.1 Composition and Phase Change Properties of Chips The phase change properties of chips containing

microencapsulated phase change material are shown in the Table 2.

The heat capacity or enthalpy of the chips depends on the content of PCMs. Obviously, the measured capacity or enthalpy of the chips is lower than the calculated value of the chips. This is probably due to the lower heat conductivity of the: chips containing microcapsule; the heat enthalpy of the microcapsule decreases. In general, the chips show a higher enthalpy or heat capacity with the increase In

microencapsulated phase change material content.

3.2 Structure and Properties of PCTF The scanning electron photomicrographs of the

cross-section of melt-spun PCT fibre is shown in Fig. 1. The sheath component was able to surround the core component containing microPCMs (Fig. l a).

HAl FENG SHI e l al.: PHOTOTHERMAL CONVERSION & THERMO-REGULATED FIBRES

Table 2- Compositi on and phase change properties of chips

Sample Content of Tm, <lC M/m , Jig Tc. oC MIe, Jig mi croPCMs, %w

S, 10 30.83 3.93 13.48 6.43

S, IS 30.75 17.93 11 .08 19.7

S, 20 32.32 33.78 11 .33 27.7

Tm- Mclting poi nt. Tc- Crystalli zation po int. L'. Hm- Heat o f melting. L'. Hc- Heat of crystalli zation. L'.H- Heat enthal py calcul ated from mi croPCMs

(a)

MI. JIg

15.69

23 .53

3 1.37

(h)

Fig. I- Scanning e lectron photomicrographs of the cross-section of PCTF at (a) x 300 magnification, and (b) x2400 magnificati on

The cross-section of the PCT fibre has some holes that are possibly due to the thermal degradation of microcapsule wall and re lease of microcapsule core material (Fig. I b). The reasons still need to be further studied.

Table 3- Composi tion and mechanical properti es of PCTF

Property HT I HT 2 HT 3

MicroPCM s content in fibre. %w 6 9 12 Zirconium carbide content , %w 4 4 4 Sheath/core ratio 4:6 4:6 4:6 Titer, dtex 6.0 5.4 7.4 Tenac ity, cN/dtex 1.73 2.19 1.36 Elongation, % 29.0 3 1.9 30.5 Tm, oC 30.14 30.23 30.2 1 L'.Hm, Jig 2.11 5.16 8.44 Tc,oC 13.36 10.26 10.57 L'.Hc,J/g 1.99 2.6 5.45

9

The composition and mechanical properties of PCTF are shown in the Table 3. The microPCMs content of the PCTF is in the range o f 6-12% which is higher than that of the melt-spun PP or PST fibre containing 3% (w/w) microPCMs6

. The factors that affect the tenacity and elongation of PCT fibre are content of microPCMs, polymer type and sheath/core ratio. HTI, HT2 and HT3 refer to the PCTF samples containing 6%, 9%

3.3 Temperature Regulation Ability

Using the same mass per unit area, the temperature regulation ability was measured between the PCTF nonwoven samples and the PP nonwoven (control). It is observed that all the PCTF samples show temperature regu lation ability as compared to control (Table 4). The higher the microPCMs content, the higher is the heat storage and thermo-regulated ability of textile. The microcapsule incorporated into fibre

and 12% amount o f microPCMs respcctively

Table 4- Temperature reg ulation properties of PCTF nonwoven

Sample Max. temp. Max . heat Max.heat Max.temp difference absorbing releasing diffe rence

°c temp. , oC temp. , "c "c

HTI 2.6 28.3 22.8 3.3 HT2 2.7 30.2 23.2 5.4 HT3 4.5 29.4 24.4 6.5

10 IN DIAN J. FIBRE TEXT. RES. , MARC H 2004

0 •

~ . -1 \ /~~~ f // \ / / .U -2 . ' . A" . / It ,.--A,.--A /

\,,·y~ / ci f-U, .. / f- -3

\ ,i - . - HT3 - . - HT2

-4 . / - A- HT1 \ / .

• - . _ • ...-m

-5 I 0 5 10 15 20

Time, min

Fi g. 2- Difference in temperatu re between PP sample (control ) and PCT F sample during te mperature ri sing process

7 - . - HT3 - . - HT2

6 - A- HT1

5

.u 4

ci t-;- 3 (/)

f-

2

o +-..---,~--,---r-,.....,~~ ... - I I I I I I' I I •

-2 0 2 4 6 8 10 12 1 4 16 18 20

Time, min

Fig. 3 -Difference in tempe rature between PP sample (con tro l) and PCTF sampl e during temperature decreasing process

melts and absorbs heat energy with increasing temperature. The temperature of PCTF nonwovens was lower than that of PP control and the superheating phenomenon did not occur. During the process of melting and beat absorbing, the nonwovens containing microPCM s can show thermo-regul ating effect (Fig. 2) . On the contrary, the temperature of PCTF nonwovens was hi gher than that of PP control due to the PCM crystalli zat ion and heat releas ing. The nonwovens containing microPCMs show heat­retaining effect but do not show supercooling phenomenon (Fig. 3) . However, to enhance thermal performance of tex tile, the microPCMs incorporated into fibre should be as high as poss ible.

32

30

28

26

.U 24 II

_2 22 ~ Q)

~ 20 E Q)

t- 18

16

14

12

o I

10 20 30

Time,min

40

I-A-pp 1 - e - HT2

50 60

Fig. 4 - Temperature ri sing or temperature dec reas ing curve between HT2 sample and PP sample (control)

3.4 Photother mal Conversion Ability Using the same mass per unit area, the

photothermal conversion ability was measured between the PCTF nonwoven and the PP nonwoven (control) . The sample containing 4% (w/w) zi rconium carbide and 9% microPCMs (HT2) was selected to study the photothermal conversion ability. Compared to the polypropylene nonwoven, the HT2 nonwoven has better heat storage and heat insulation properti es. The maximum difference in temperature of two types of nonwoven is S.7°C when exposed to near in frared ray_ The minimum difference in temperature between PCTF sample and PP sample is 2.2°C when the lR ray is cut off (Fig. 4). The results show that the PCT f ibre has better light absorbing property in the near infrared ray and visible light. The PCT fibre can convert the near infrared and visible li gh t into heat energy much easier than PP.

4 Conclusions 4.1 The photothermal conversion and thermo­regulated sheath/core composite fibre has been , for the first time, successfully melt spun with the chips Llsing polyethylene mixed with microencapsulated phase change material as core and polypropylene containing photothermal convers ion ceramic as sheath_ 4.2 The content of microPCMs in the PCT fibre can be varied up to 12% (w/w), which is higher than that of the PAN or PBT fibre . Further work should be foc used on how much amount of microencapsulated phase change material can be incorporated into the spinning of chemical fibre and on the study of the relationship between the amount of microPCMs in

HAl FENG SHI et al.: PHOTOTHERMAL CONVERSION & THERMO-REGULATED FIB RES 1 ]

textile and the comfortable performance of the human body. 4.3 The maximum heat absorbing temperature difference is 4.5°C and the maximum heat releasing temperature difference is 6.5°C when the PCTF nonwoven is compared with PP nonwoven. 4.4 When exposed to the near infrared ray, the temperature rising rate of PCTF nonwoven is evidently faster than that of polypropylene nonwoven . The maximum difference in temperature of two types of nonwoven is 5.7 °C when exposed to near infrared ray. The minimum difference in temperature between photothermal conversion fibre nonwoven and PP sample is 2.2°C when the IR ray is cut off. The results show that the PCT fibre is able to not only convert the near infrared ray to heat energy, but also to regulate the inner temperature.

Acknowledgement The authors are thankful to the National Natural

Science Foundation of China (No. 30073015) and the Tianjin Natural Science Foundation (No. 003801711) for providing the financial support.

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