Variable temperature cure polyetherimide epoxy-based prepreg systems

This work identifies the necessary attributes of variable temperature cure epoxybased prepreg systems as they relate to high performance prepreg systems capable for composite repair. Model polyetherimide epoxy blend resins were developed and hot-melt impregnated into woven carbon fabric and compared with a commercial prepreg system. It was found that when the PEI content was increased from 0 to 14 wt% in the base resin of the prepregs, the G_IC and G_IIC fracture toughness increased by over 70%. The fracture toughness was found to be similar when the model prepreg was cured at either 121°C or 177°C, a result of only a 9% difference in conversion and complete phase separation of the PEI at both cure temperatures. Void content in vacuum cured laminates were found to decrease as the PEI content was increased because of a large quantity of resin in the interstitial areas between the longitudinal and transverse tows. A comparison of the model and commercial prepreg system demonstrated many similarities and some significant differences. For example, the commercial prepreg had a 15% difference in conversion when cured at 121°C versus 177°C and very little PEI phase separation after both cure cycles. As a result, a significant difference in G_IIC for the commercial prepreg was observed for the two cure temperatures.     

一种中温固化绿色固化剂树脂预浸料研究

采用松香酸酐(RMA)固化剂研制一种中温固化绿色固化剂环氧树脂,浸渍玻璃纤维织物得到中温固化绿色固化剂树脂预浸料。研究结果表明:3233C/EW250F玻璃布预浸料材料的理化性能、力学性能、燃烧性能、电性能和耐热性与3233B树脂/EW250F玻璃布复合材料性能相当,满足79AD Style 1581 Class 3 Grade B技术规范要求。     

Radiation-curable prepreg composites

Advanced composites, specifically carbon-fiber-reinforced epoxies, are used extensively for a variety of demanding structural applications, primarily because of their high strength-to-weight and stiffness-to-weight ratios, corrosion resistance, and damage tolerance characteristics. Electron beam (EB) treatment can be used to produce useful physical and/or chemical changes in plastics and composites by initiating various polymerization and crosslinking reactions. The advantages of using EB rather than thermal curing for carbon-fiber-reinforced epoxy composites include curing at ambient temperature, reduced curing times, and fewer volatiles. An EB-curable carbon fiber-acrylated epoxy composite is being developed for various applications. The tensile properties of the 14-ply EB-cured epoxy laminate were comparable with the properties of the thermally cured laminates used in the aircraft industry. Research is continuing to develop resin formulations and select coupling agents to improve the compression properties of EB-cured laminates.     

Room temperature aging of Narmco 5208 carbon-epoxy prepreg. Part I: Physicochemical characterization

Samples of Narmco Rigidite 5208/WC3000 carbon-epoxy prepreg were exposed to ambient temperature (22°C) and 50% relative humidity for different periods up to 66 days. They were analyzed in depth using various techniques to determine the extent of the chemical changes occurring. The physicochemical techniques used were Fourier transform infrared spectroscopy (transmission, attenuated total reflection, diffuse reflection), liquid chromatography (reverse-phase, high-speed reverse-phase, and high-performance size-exclusion), thermal analysis (differential scanning calorimetry and thermogravimetric analysis), and pyrolysis-gas chromatography. All showed evidence of significant changes, the most sensitive being Fourier transform infrared spectroscopy (FT-IR) and reversephase liquid chromatography (RPLC). FT-IR showed that the number of unreacted epoxy groups decreases steadily at a rate of 0.34% per day, based on the initial amount. At the same time, the number of free amine-hardener molecules, as monitored by RPLC, drops at a rate of 1.05% per day. RPLC also showed that the amount of initial epoxy-amine reaction product increases significantly over the first 30 days, but then declines as it undergoes further reaction to give higher-molecular-weight products. The heat of polymerization of the resin, measured by thermal analysis, decreased by 0.26% per day from its initial value of 561 J/g.     

Determination of prepreg tack

Prepreg materials — fibre-reinforcement preimpregnated with uncured resin — are widely used for the manufacture of large composite material components. Current commercially available prepreg materials often show significant variations in tack strength, from point to point within a sheet and from sheet to sheet. Such inconsistencies can lead to void formation in the final composites laminate. This paper describes the techniques and apparatus developed for the investigation of the surface tack strength of adhesives in general and of prepreg materials in particular, as a function of contact time and pressure and of rate of separation. It is hoped that the more detailed knowledge of prepreg tack will enable the production of more consistent material and hence the manufacture of improved quality composite laminates.     

SP launches blade prepreg

A GLASS fibre prepreg for use in making wind turbine blades was unveiled by UK-based company SP at the European Wind Energy Conference in Spain in June.This is a short news story only. Visit www.reinforcedplastics.com for the latest plastics industry news.     

预浸料技术的新进展

本文根据复合材料低成本制造技术，介绍了预浸料技术的新进展，包括可常温储存的预浸料；低温固化高温使用的预浸料；大丝束碳纤维预浸料和快速固化预浸料。     

Radiation-curable carbon fiber prepreg composites

Radiation processing is the utilization of ionizing radiation, usually photons or electron beams, to produce useful physical and chemical changes in a material. A potential application for electron beam processing for composite manufacturing is for curing carbon fiber prepregs. These prepregs, carbon fibers or fabrics preimpregnated with liquid polymer resin, are commonly used in the aircraft industry. Their use, however, can be time consuming and labor intensive. The advantages of radiation curing over thermal or chemical curing methods include improved rate control, reduced curing times, and curing at ambient temperature. There is no need for chemical initiators. A radiation-curable prepreg has been designed to meet the mechanical and physical property specifications of a leading aircraft manufacturing company. The resin is a mixture of an expoxy diacrylate, polybutadiene diacrylate, and a multifunctional monomer. This resin was used to impregnate a plain weave carbon fabric, at a loading of 35 percent (by mass), using a solvent process. Preliminary characterization studies show that the cured polymer produced by irradiation in air to a dose of 40 kGy is amorphous with a maximum gel fraction of 85 percent. The softening point of the polymer varied from 228°C (30-kGy sample) to 237°C (50-kGy sample). The linear thermal expansion coefficient of the polymer was 1.7 × 10⁻⁴ m/m°C from 25°C to 150°C and was unaffected by varying the applied dose from 30 to 50 kGy.