PET容器应力开裂的科学探讨

自1978年位于美国马萨诸塞州福尔河的制罐公司研发生产2升整体PET瓶以来,应力开裂一直是PET容器的致命点。随之,出现了很多有关影响应力开裂的原因分析和补救措施。这些分析既不完全正确也不完全错误,需要时间来验证。只有通过科学的探讨才能找到有用的信息,从中得到的经验和教训既适用于PET瓶,也适用于一般的塑料瓶成型。[第一段]     

聚酯(碳酸饮料)瓶应力开裂解决方法

通过对应力开裂机理进行研究和讨论,找出了影响碳酸饮料瓶应力开裂的因素．提出了解决思路和方法,并在生产实践中对制瓶工艺进行优化,最终解决了碳酸饮料瓶的应力开裂技术难题。     

PET瓶的等离子处理技术——ACTIS

一、　等离子（ＡＣＴＩＳ）技术原理ＡＣＴＩＳ技术是法国西得乐公司开发的、利用等离子技术在ＰＥＴ瓶内壁上,涂布一层碳氢阻隔层制备高阻隔性塑料瓶的一种新方法。等离子法（ＡＣＴＩＳ）是将气态的乙炔导入ＰＥＴ瓶中,通过微波处理器将乙炔激化,使之呈等离子状态,等离子态的颗粒撞击在瓶壁上能量骤然消失,在壁上形成一层极薄而致密的固态涂层（高度氢化的无定型碳涂层）,涂层的厚度不到２００Ａ,一只容量为５００ｍｌ的ＰＥＴ瓶的涂层,仅８～９毫克,但却具有极佳的阻透性能。二、　等离子（ＡＣＴＩＳ）技术的工业化装置ＡＣＴ…     

硫化物应力腐蚀开裂试验应力环载荷的测量及标定

硫化物应力腐蚀开裂试验的常用载荷测量方法是通过测量应力环的变形量计算载荷。指出了该方法在标定和测量过程中容易产生较大误差的原因。通过测量对比,证明了采用载荷传感器直接测量载荷的方法可减小误差,更适合作为试验过程中的载荷标定方法。     

残余应力对包装机械腐蚀开裂的影响及对策研究

包装机械零，部件在制造过程，内部都会产生残余应力，通过实验阐述了残余应力对包装机械腐蚀开裂性能的影响，以及防止腐蚀开裂的措施。     

面向残余应力检测的聚碳酸酯在溶剂环境下的初始应力-开裂时间关系

本研究利用四点弯曲应力松弛实验装置,获得了聚碳酸酯(PC)材料在不同比例甲苯/正丁醇混合溶剂中的初始应力-开裂时间实验数据;依据离散数据的几何相似性,建立了一个指数关系模型,拟合得到了初始应力-开裂时间的连续分布,并基于对拟合曲线的抽样误差分析,建立了残余应力与初始应力之间的关系式,可用于提高PC制品残余应力的检测精度。     

输油软管开裂原因

某飞机输油软管发生漏油现象,经检查为软管开裂所致.采用宏观观察、断口分析、红外光谱分析和热失重试验等方法,对软管开裂的原因进行了分析.结果表明:输油软管的开裂性质为疲劳开裂,裂纹起源于螺纹凹槽的根部;输油软管装配后产生应力老化,导致其疲劳性能下降,在振动和内部燃油压力等交变应力的作用下裂纹从凹槽根部的损伤位置起源,并最...     

钛合金螺母开裂原因分析

钛合金螺母在使用过程中发生了开裂,采用化学成分分析、金相分析、微观观察等方法对开裂螺母进行了分析。结果表明螺母的开裂是由于应力腐蚀造成的,并提出改进措施。     

Effect of recycled content and rPET quality on the properties of PET bottles,part I: Optical and mechanical properties

The effect of recycled content and type of recycled poly (ethylene terephthalate) (rPET) on the haziness; colour parameters L*, a*, and b*; total colour change; ultraviolet-visual spectrum (UV-VIS) absorption; and environmental stress cracking (ESC) of PET bottles was studied. Three series of PET bottles were made at a small scale production facility with same type of virgin PET and three different types of rPET with recycled contents of 25%, 50%, 75%, and 100%. Also, the particle contamination of the produced PET bottles was studied by dissolving bottle fragments and counting the insoluble particles. A linear relationship was found between the haziness of PET bottles and the particle contamination, with a coefficient of determination of 0.96. Linear relationships were also found between the colour parameters L* and b* and the particle contamination of the PET bottles, but the slope differed for each type of rPET. The origin of rPET (mono-collection or cocollection) seems to be the crucial factor determining particle contamination and colour of the produced bottles. No correlation was found between the recycled content and the incidence of ESC. However, PET bottles in which high intrinsic viscosity (IV) values were measured showed lower chances of ESC than PET bottles with low IV values     

Effect of hydrogen on stress corrosion cracking of copper

The effects of hydrogen on electrochemical behavior and susceptibility of stress corrosion cracking (SCC) of pure copper were studied. SCC susceptibility of pure copper in a 1 M NaNO₂ solution was increased by pre-charged hydrogen. The effect of hydrogen on the susceptibility is more obvious in the low stress region due to the longer fracture time, which resulted in a longer time for more hydrogen to diffuse toward the crack tip. Synergistic effects of hydrogen and stress on corrosion and SCC processes were discussed. The results showed that an interaction between stress and hydrogen at the crack tip could increase the anodic dissolution rate remarkably.     

Evaluation of a UV absorber added to PET bottles for edible oil packaging

The photo‐oxidation of lipids has significant effects on the quality of edible oils. The oxidation of oils and fats can begin due to the action of external energy sources such as light. Studies showed that the rate of photo‐oxidation of the oil depends on the light transmission of the packaging, the product characteristics and the O₂ barrier of the packaging. The UV absorber 2‐(2′‐hydroxy‐3′‐tert‐butyl‐5′‐methylphenyl)‐5‐chlorobenzotriazole (Tinuvin 326^?) has been used in PET bottles for oil, making possible the reduction of the photo‐oxidation rates. This additive was approved recently by the European Union and included in the Positive List of Directive 2001/62/EC, with a limit of specific migration. This additive is also approved by the Mercosur legislation; nevertheless its restriction of use is being reviewed in Brazil. This study had the objectives of evaluating the efficiency of the additive through the determination of the light barrier properties of PET bottles with various levels of Tinuvin 326^? and of verifying its suitability for use in direct contact with foods. Copyright © 2003 John Wiley & Sons, Ltd.     

BaTiO3铁电陶瓷的应力腐蚀

研究了BaTiO3铁电陶瓷在恒载荷下的应力腐蚀,环境分别为湿空气、水、硅油和甲酰胺.结果表明,BaTiO3铁电陶瓷在湿空气、硅油、水和甲酰胺中都能发生应力腐蚀,其本质是介质分子吸附降低表面能.在空气中的瞬时断裂为穿晶断裂,滞后断裂大部分为穿晶断裂,局部为沿晶断裂.在这四种环境中,归一化应力腐蚀门槛应力强度因子分别为KIsCC/KIC=0.78(空气),0.63(水),0.66(硅油)和0.82(甲酰胺),其断裂韧性为KIC=1.29±0.14 MPa·m1/2.     

Effect of recycled content and rPET quality on the properties of PET bottles,part II: Migration

Polyethylene terephthalate (PET) bottles were produced from three types of recycled PET (rPET) with four levels of recycled content. The migration of substances from these bottles to water was studied. Several migrated substances were detected. The migrated amounts of acetaldehyde and ethylene glycol complied with the limits given in the food contact material (FCM) legislation. Migration of 2-methyl-1,3-dioxolane was below the limit of 10 μg·L⁻¹, which is conventionally applied for non-intentionally added substances (NIAS) not classified as ‘carcinogenic’, ‘mutagenic’ or ‘toxic to reproduction’ (CMR). Limonene, acetone, butanone and furan were also detected as migrants, of which limonene is a natural fragrant, and the other three are probably residues from solvents used to clean and protect the mould at the small-scale production facility. Finally, benzene and styrene were also found as migrants from rPET. These migrants appear to originate from heat-induced reactions within the PET matrix, which involve contaminants. The formation of benzene in rPET is attributed to polyvinylchloride as contaminant. The migrated amounts of benzene from the PET bottles with recycled content to the water simulant are relatively small (0.03–0.44 μg·L⁻¹) after 10 days at 40°C. Consequently, the margin of exposure is 3.10⁵–8.10⁶. Hence, the level of concern for the public health is low, and the migrated amount represents a low priority for risk management. The FCM legislation demands a risk assessment for migrating NIAS. Depending on the underlying data and exposure scenario, different threshold limits in the food can be derived which can still be considered as safe.     

TEM investigations of intergranular stress corrosion cracking in austenitic alloys in PWR environmental conditions

Abstract

Analytical transmission microscopy has been used to investigate the initiation of stress corrosion cracking in Inconel 600 subjected to constant load testing under simulated pressured water reactor primary water conditions. The observations revealed that intergranular attack proceeded by the development of a zone of polycrystalline chromia along the boundary plane intersecting either the free surface or a blunted, open crack in contact with the free surface. Ni-rich metal particles were interspersed within the chromia. Conversely, open cracks were filled with nanocrystalline NiO and large compound particles of spinel and NiO, indicating a difference in potential between closed, attacked boundaries and open cracks. Open cracks appeared to have initiated by fracture of the chromia zones, such fracture being strongly dependent on boundary geometry with respect to loading direction. The observations suggest that stress corrosion crack initiation and propagation is dependent on diffusion of oxygen through the porous oxides. Dislocations and stress could enhance diffusion as chromia was observed along slip planes at the arrested tips of blunt cracks.     

Damage due to hydrogen embrittlement and stress corrosion cracking

Damage of metals due to the influence of hydrogen and to stress corrosion cracking is quite frequent and leads to dangerous failures as well as to loss of property and large compensational payments by insurance companies. One reason for this, is that some designers and engineers seem to lack sufficient knowledge of the basic mechanisms of these phenomena and accordingly often have only vague ideas how to prevent such failure causes. Although the basic concepts can be found in a number of good text books it seems worthwile to recall them in a short comprehensive paper.     

Interplay of microbiological corrosion and alloy microstructure in stress corrosion cracking of weldments of advanced stainless steels

This paper presents an overview of the phenomenon of stress corrosion cracking (SCC) of duplex stainless steels and their weldments in marine environments and the potential role of microbial activity in inducing SCC susceptibility. As a precursor to the topic the paper also reviews the performance of the traditional corrosion-resistant alloys and their weldments and the necessity of using duplex stainless steels (DSS), in order to alleviate corrosion problems in marine environments. Given that the performance of weldments of such steels is often unsatisfactory, this review also assesses the research needs in this area. In this context the paper also discusses the recent reports on the role of microorganisms in inducing hydrogen embrittlements and corrosion fatigue.     

Failures of engineering components due to environmentally assisted cracking

Examples of failures of engineering components by stress-corrosion cracking, corrosion-fatigue, hydrogen embrittlement, liquid-metal embrittlement, and solid-metal embrittlement are described. Causes of failure include inappropriate materials selection or heat treatment, poor design, and high residual stresses. The examples illustrate how fractographic characteristics, analysis of films and deposits on fracture surfaces, and other factors help in diagnosing the modes and causes of failures, thereby enabling the appropriate remedial measures to be taken.