摘要
塑料物证是微量物证实验室常见的物证之一。目前对塑料物证的检验主要用红外光谱法检验塑料的种类,用扫描电镜/能谱法检测塑料中添加剂。但有些塑料样品,如汽车大灯塑料和家用保鲜膜,厂家为了保证其使用功能,很少加入添加剂,塑料种类并不多,这就给塑料物证比对检验带来很大困难。配有小角光散射检测器的凝胶色谱,无需标准样品就可直接测量塑料绝对分子量及其分布,对于种类相同的塑料物证可做进一步区分。本文采用常温凝胶色谱法对4个汽车大灯灯罩塑料进行检验,高温凝胶色谱法对3个保鲜膜塑料进行检验,得到这些样品的重均分子量(Mw)、数均分子量(Mn)和分子量分布(多分散指数PDI)。分别采用Student,s t检验法对组内样品的检测数据进行比对,综合Mw、Mn和PDI三个参数对样品进行区分。通过凝胶色谱法检验及Mw、Mn和PDI 3个参数的Student,s t检验,可对用扫描电镜/能谱法和红外光谱法无法区分的4个汽车大灯塑料样品和3个保鲜膜样品实现完全区分。该方法为塑料物证的区分提供了一种新的检验手段。
Polymers are frequently encountered in trace evidence laboratories in crime scene investigation, various types of plastic products can be collected. Fourier Transform Infrared Spectroscopy （FTIR） is usually used to determine the type of polymers and Scanning Electron Microscope/Energy Dispersive X-ray Spectrometry （SEM/EDX） is used to determine the elements of additives in polymer samples. Molecular weight and molecular weight distribution are important parameters to characterize polymers, but they have not been used in forensic science before. For some plastic samples, there is no or few additives present in them, which makes the differentiation between them more dififcult. In many cases, the polymer type and the additives information are not enough to differentiate plastic samples. Molecular weight and molecular weight distribution will be a big help to differentiate polymer samples of the same type. Gel Permeation Chromatography （GPC） with low angle laser light scattering detector is very useful in determining molecular weight and molecular weight distribution of polymers even without the relative standards. In this paper, four automobile headlight screens and three preservative iflm samples were analyzed by GPC method to determine the molecular weight and molecular weight distribution. Weight average（Mw）, number average（Mn）and molecular weight distribution or polydispersity index （PDI） of samples were measured. Normal temperature GPC method was applied for examining the automobile headlight screens and high temperature GPC method was used for examining preservative film samples. Student’s t test was used to compare the mean value of Mw, Mn and PDI of pairs of samples. The results show that all the plastic samples can be differentiated by the combination of these three parameters. GPC method provides a new way to further examine the plastic samples which could not be differentiated by FTIR and SEM/EDX.
出处
《刑事技术》
2015年第3期208-210,共3页
Forensic Science and Technology
基金
中央级公益性科研院所基本科研业务费项目(No.2013JB012)
关键词
塑料物证
凝胶色谱
分子量
分子量分布
plastic evidence
gel permeation chromatography
molecular weight
molecular weight distribution
