Gas Chromatography in Analysis of Polymers and Rubbers

M. Hakkarainen, S. Karlsson
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引用次数: 8

Abstract

This chapter gives an overview of gas chromatography (with mass spectrometry) (GC/MS) of polymers and rubbers. Gas Chromatography (GC) analyzes volatile organic compounds, with an upper limit of 350°C, which means that the compounds to be analyzed must be volatile below this temperature. The technique is able to analyze small quantities of material, which means that it is applicable for example to residual monomers, initiators, catalysts, some additives and degradation products of polymers. It is generally not suitable for analysis of organic compounds at high molecular weight or of low volatility. Care must be taken not to analyze reactive species, which may ruin columns or other parts of the equipment. Proper sample preparation is necessary before GC/MS. Sensitive and selective techniques are used to separate and extract low-molecular-weight organic compounds from polymers. The sample preparation–extraction techniques may be grouped into (1) solvent extraction from solid matrices, (2) solvent extraction of organic compounds from aqueous solutions containing polymer (e.g. biomedical implants in physiological buffers) and (3) solvent-free extraction methods. An ideal extraction method is quantitative, selective, rapid and uses little or no solvent. Soxhlet is the old and traditional method for solvent extraction from solid sample matrices. Soxhlet is, however, time-consuming (two or three days is not uncommon), nonselective, uses large volumes of solvents and is often not quantitative. Ultrasonication and microwave-assisted extraction (MAE) are instead much more effective. Ultrasonication works by agitating the solution and producing cavitation in the liquid. The technique is useful for example to extract antioxidants from polyethylene (PE). MAE, extracts (semi)volatiles from solid matrices and has been successfully used to extract additives from polyolefins, aroma and flavor compounds from recycled polymers, and oligomers from poly(ethylene terephthalate) (PET). Solvent extractions from aqueous solutions are liquid–liquid extraction (LLE) and solid-phase extraction (SPE). LLE is rapid, but lacks in selectivity, is labor intensive and uses large volumes of organic solvents. SPE is instead suitable for separating volatile and semivolatile compounds and is a physical extraction process involving liquid and a solid phase (sorbent). Examples of separations are degradation products of PE and hydroxyacids in buffer solutions. Solvent-free extraction methods are headspace gas chromatography (HS/GC), solid-phase microextraction (SPME) and supercritical fluid extraction (SFE). HS/GC determines volatile compounds in liquids and solids. SPME is an inexpensive, rapid and solvent-free technique with applications reported for air samples, water and soil, based on 1-cm long, thin fused silica fiber coated with a polymeric stationary phase mounted in a modified syringe. The stationary phase is available in four different kinds. SFE uses a supercritical fluid to penetrate a material. Applications are antioxidants in polyolefins, aroma vapors absorbed in PE and surface coatings and their raw materials. This article reports applications in synthesis-related compounds in polymers, HS (headspace) analysis of polymers in indoor environments, thermal degradation products of polymers at processing temperatures, environmental degradation products, and additive systems in plastics and coatings.
气相色谱法分析聚合物和橡胶
本章概述了聚合物和橡胶的气相色谱(质谱)(GC/MS)。气相色谱(GC)分析挥发性有机化合物,其上限为350℃,这意味着要分析的化合物必须在此温度以下挥发。该技术能够分析少量的材料,这意味着它适用于残余单体、引发剂、催化剂、一些添加剂和聚合物的降解产物。它一般不适合分析高分子量或低挥发性的有机化合物。必须注意不要分析反应性物质,这可能会破坏色谱柱或设备的其他部分。在GC/MS之前,必须进行适当的样品制备。灵敏和选择性技术用于从聚合物中分离和提取低分子量有机化合物。样品制备-提取技术可分为(1)从固体基质中溶剂提取,(2)从含有聚合物的水溶液中溶剂提取有机化合物(例如,生理缓冲液中的生物医学植入物)和(3)无溶剂提取方法。一种理想的提取方法是定量、选择性、快速、少溶剂或不使用溶剂。索氏法是从固体样品基质中提取溶剂的古老而传统的方法。然而,索氏法耗时(两到三天并不罕见),无选择性,使用大量溶剂,而且通常不能定量。超声波和微波辅助提取(MAE)更有效。超声波的工作原理是搅动溶液并在液体中产生空化。该技术可用于从聚乙烯(PE)中提取抗氧化剂。MAE是从固体基质中提取(半)挥发物,并已成功地用于从聚烯烃中提取添加剂,从回收聚合物中提取香气和风味化合物,从聚对苯二甲酸乙酯(PET)中提取低聚物。水溶液的溶剂萃取分为液-液萃取(LLE)和固相萃取(SPE)。LLE快速,但缺乏选择性,是劳动密集型的,使用大量的有机溶剂。SPE适用于分离挥发性和半挥发性化合物,是一种涉及液体和固相(吸附剂)的物理萃取过程。分离的例子是PE和羟酸在缓冲溶液中的降解产物。无溶剂萃取方法有顶空气相色谱法(HS/GC)、固相微萃取法(SPME)和超临界流体萃取法(SFE)。HS/GC测定液体和固体中的挥发性化合物。SPME是一种廉价、快速、无溶剂的技术,据报道可用于空气样品、水和土壤,该技术基于1厘米长、薄的熔融二氧化硅纤维,表面涂有聚合物固定相,安装在改良的注射器中。固定相有四种不同的类型。SFE使用超临界流体穿透材料。应用于聚烯烃的抗氧化剂,PE和表面涂层及其原料中吸收的芳香蒸汽。本文报道了在聚合物合成相关化合物、室内环境下聚合物的顶空分析、聚合物在加工温度下的热降解产物、环境降解产物以及塑料和涂料添加剂体系中的应用。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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