Cracking analysis of PC component initiated by plasticized PVC

doi:10.19491/j.issn.1001-9278.2025.10.010

Abstract

Abstract:

This study investigates the root cause of cracking in the screw areas of a polycarbonate （PC） connector assembled within a device. A combination of analytical techniques， including differential scanning calorimetry， thermogravimetric analysis， gas chromatography⁃mass spectrometry （GC⁃MS）， and Fourier⁃transform infrared spectroscopy， was employed to compare cracked and normal samples. GC⁃MS analysis identified dibutyl phthalate （DBP）， a plasticizer， exclusively in the cracked components. The source of the DBP was traced to a polyvinyl chloride （PVC） soft tube installed through the connector. Hansen solubility parameter analysis confirmed a high affinity between DBP and PC （with a relative energy difference， RED， of 0.72）， indicating DBP's capability to solubilize and plasticize the PC matrix. The failure mechanism was identified as environmental stress cracking （ESC）： DBP migrated from the PVC tube into the PC housing， reducing its cohesive strength and enabling brittle fracture initiation under the stress concentrated at the screw threads. This case provides a classic example of ESC and highlights the critical need for compatibility screening between adjacent polymer components and their additives.

Key words: polyvinyl chloride, polycarbonate, dibutyl phthalate, environmental stress cracking, solubility parameter

CLC Number:

TQ325.3

LIU Zhongping, XIAO Yinhe, GE Huijun. Cracking analysis of PC component initiated by plasticized PVC[J]. China Plastics, 2025, 39(10): 54-59.

Figures/Tables 14

Fig.1. The assembled state and cracked location of the connector

Fig.2. SEM of the cracked areas on the connector

Fig.3. FTIR spectra of the main body for cracked sample and normal sample

Fig.4. DSC curves of the main body for cracked sample and normal sample

Fig.5. TG curves of the main body for cracked sample and normal sample

样品	T_g/^oC	T_onset/^oC	残留质量/%
未断裂样品	146.5	467.0	20.5
断裂样品	146.3	468.4	20.25

Tab.1. Results of DSC and TG tests

Fig.6. Total ion chromatograms of volatiles from the areas near the screw of cracked sample and normal sample

Fig.7. MS spectra of volatiles from the cracked sample at the retention time 25.3 minute

Fig.8. FTIR spectra of cracked area of cracked sample， the body of normal sample and DBP

Fig.9. GC spectra of volatiles from the rubber sealing pad， the tube of cracked sample and the tube of normal sample

Fig.10. MS spectra of volatiles from the tube of the cracked sample at the retention time 25.3 minute

材料	δ_D/MPa^1/2	δ_P/MPa^1/2	δ_H/MPa^1/2	Ro/MPa^1/2
PC	18.1	5.9	6.9	5.5
PA66	16	11	24	3
DBP	17.8	8.6	4.1

Tab.2. The Hansen parameters of PC， PA66 and DBP

材料组合	Ra/MPa^1/2	RED
PC⁃DBP	3.94	0.72
PA66⁃DBP	20.36	6.79

Tab.3. The solubility parameter distance and RED number of PC with DBP and PA66 with DBP

Fig.11. Diagram of ESC process

References 19

[1]	Al⁃Saidi Lutfi F， Mortensen Kell， Almdal Kristoffer. Environment stress cracking resistance. Behaviour of polycarbonate in different chemicals by determination of the time⁃dependence of stress at constant strains ［J］. Polymer Degradation and Stability， 2003， 82（3）： 451⁃461.
[2]	何洋，李洋洋，邵景昌，等. PC制件内应力表征及内应力开裂因素与改善措施分析［J］. 中国塑料，2019， 33（7）： 63⁃68.
	HE Y， LI Y Y， SHAO J C， et al. Characterization， analysis and improvement of internal stress cracks of PC［J］. China Plastics， 2019， 33（7）：63⁃68.
[3]	江盛玲，华幼卿. 聚碳酸酯耐环境应力开裂性能的研究［J］. 塑料工业，2011， 39（5）： 82⁃85+112.
	JIANG S L， HUA Y Q. Study on environmental stress crack resistance property of polycarbonate［J］. China Plastics Industry， 2011， 39（5）： 82⁃85+112.
[4]	Mônica Martiniano Ferreira，Vanessa de Freitas Cunha Lins. Failure in automobile headlight lenses ［J］. Engineering Failure analysis， 2019， 104： 844⁃855.
[5]	周啸，何向明. 聚合物性能与结构［M］. 北京：清华大学出版社，2015： 71⁃84.
[6]	Khalid Yasir， Achour Amine， Muhammad Aftab Akram，et al. Polycarbonate/titania composites incorporating TiO₂ with different nanoscale morphologies for enhanced environmental stess cracking resistance in dioctyl phthalate ［J］. Polymers， 2022， 14（17）： 3 693.
[7]	Bok Nam Jang， Charles A， Wilkie A.TG/FTIR and mass spectral study on the thermal degradation of bisphenol a polycarbonate［J］. Polymer Degradation and Stability， 2004， 86（3）， 419⁃430.
[8]	高欢，卫碧文，付饶，等. 气相色谱⁃质谱法测定欧盟REACH法规相关的15种邻苯二甲酸酯的含量［J］. 化学研究与应用， 2021， 33（11）： 2 262⁃2 268.
	GAO H， WEI B W， FU R， et al. Determination of 15 phthalate esters restricted by EU REACH by GC⁃MS ［J］. Chemical Research and Application， 2021， 33（11）： 2 262⁃2 268.
[9]	樊小军，刘晓暄，崔艳艳. 气相色谱⁃质谱法测定玩具中邻苯二甲酸酯增塑剂［J］. 理化检验⁃化学检测， 2013， 49（4）： 432⁃438.
	FAN X J， LIU X X， CUI Y Y. GC⁃MS determination of phthalates added as plasticizers in toys ［J］. Physical Testing and Chemical Analysis（Part B： Chemical Analysis）， 2013， 49（4）： 432⁃438.
[10]	Shen Hao⁃Yu， Jiang Hai⁃Liang， Mao Hong⁃Lei， et al. Simultaneous determination of seven phthalates and four parabens in cosmetic products using HPLC⁃DAD and GC⁃MS methods［J］. Journal of Separation Science， 2007， 30（1）： 48⁃54.
[11]	Raman Arun， Farris Richard J， Lesser Alan J. Effect of stress state and polymer morphology on environmental stress cracking in polycarbonate［J］. Journal of Applied Polymer Science， 2003， 88（2）：550⁃564.
[12]	Jansen Jeffrey A. Environmental stress cracking⁃the plastic killer［J］. Advanced Materials & Processes， 2004， 162（6）： 50⁃53.
[13]	Alperstein David， Knani Dafna， Borchmann Nikolai， et al. Prediction of environmental stress cracking in polycarbonate by molecular modeling［J］. Polymer for Advanced Technologies， 2014， 25（12）： 1 433⁃1 438.
[14]	Hansen Charles M. On predicting environmental stress cracking in polymers［J］. Polymer Degradation and Stability， 2002， 77（1）： 43⁃53.
[15]	Charles M， Hansen， Just Lisbeth. Prediction of environmental stress cracking in plastics with Hansen solubility parameters［J］. Industrial & Engineering Chemistry Research， 2001， 40（1）：21⁃25.
[16]	Hildebrand Joel H， Scott Robert L. The solubility of nonelectrolytes［M］. 3rd ed. New York： Reinhold Publishing Corporation， 1950： Charpter VII.
[17]	Charles M. Hansen. Hansen solubility parameters⁃a user’s handbook［M］. 2nded. Boca Raton： CRC Press， 2007.
[18]	卢家荣，吴水珠，赵建青，等. PC/PA6共混体系的耐溶剂性及其结晶行为的研究［J］. 塑料工业， 2008， 36（10）： 9⁃12+19.
	LU J R， WU S Z， ZHAO J Q， et al. Study of solvent resistance and crystallization behavior of PC/PA6［J］. China Plastics Industry， 2008， 36（10）： 9⁃12+19.
[19]	钱志国，尹继磊，李正梅，等. 耐化学高抗冲PC/PBT合金的制备［J］. 工程塑料应用， 2016， 44（1）： 49⁃52.
	QIAN Z G， YIN J L， LI Z M， et al. Preparation of chemical resistant and high impact PC/PBT alloys［J］. Engineering Plastics Application， 2016， 44（1）： 49⁃52.