The effect of physical ageing on the properties of poly(ethylene terephthalate)

Physical ageing rates of poly(ethylene terephthalate) have been measured, and ageing is interpreted to be associated with the conventional glass formation process, which occurs at a more rapid rate at higher temperatures. Ageing is accompanied by a marked change in mechanical properties, increased tensile yield stress and drawing stress, more localized yielding of the polymer and a marked decrease in impact strength. The fracture results have been attributed to the increased yield stress and a change in contribution of plane stress and plane strain conditions in the samples. Fracture surfaces show evidence of mixed modes of fracture.     

Self-diffusion of poly(ethylene oxide) in aqueous dextran solutions measured using FT-pulsed field gradient n.m.r.

Transport in ternary polymer₁, polymer₂, solvent systems has been investigated using an n.m.r. spin-echo technique. The dependence of the self-diffusion coefficient of poly(ethylene oxide) polymers on the concentration and molecular size of dextran in aqueous solution has been measured. Monodisperse poly(ethylene oxide) fractions ($\text{M}\text{?}{}_{\mathrm{w}}\text{=7.3×10}{}^4$, 2.8·10⁵ and 1.2·10⁶) and dextrans ($\text{M}\text{?}{}_{\mathrm{w}}\text{=2·10}{}^4$, 1·10⁵ and 5·10⁵) have been employed over a range of concentration up to the miscibility limit in each system. It is found that when the molecular size of the diffusant is commensurate with or exceeds that of the matrix polymer, a relationship of the form: $\text{(}\text{D}\text{D}{}_0\text{)}{}_{\mathrm{<mtext>PEO</mtext>}}\text{=}\text{exp}\text{?k(C[η])}$ is applicable, where C[η] refers to the dextran component and is considered to describe the extent of coil overlap in concentrated solution. ($\text{D}\text{D}{}_0$) is independent of the molecular size of the poly(ethylene oxide), at least in the range studied (M_w<300 000).     

Change in the molecular weight distribution of poly(ethylene oxide) caused by the complexation with poly(acrylic acid)

The complexation between poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA) was made by using double the molar quantity of either polymer component at pH 2 where the resulting complex completely precipitates. After the removal of the precipitate, PEO or PAA remaining in the supernatant was subjected to gel permeation chromatography to investigate the change in the molecular weight distribution (MWD) caused by the complexation. No remarkable difference is observed in the MWD curves for PEO[1] (M_w=1.37 × 10⁴) before and after the complexation with PAA[1] (M_w=1.10 × 10³) and PAA[2] (M_w=4.16 × 10⁵). However, the MWD curves of PEO[2] (M_w=1.26 × 10⁵) and PAA[2] become shortened and shift to the low molecular weight side after the complexation with PAA[1] or [2] and PEO[2], respectively. This tendency is enhanced by increasing the complexation temperature. From these results, it is indicated that the complexation between PEO and PAA deals with an equilibrium reaction, and the equilibrium constant is dependent on the chain length of both polymer components and also on the complexation temperature.     

Change of the amorphous state by heat treatment below the glass transition temperature

This study was undertaken to elucidate the state of a polymer in the amorphous state through a change of motion of the molecular chain caused by heat treatment below the glass transition temperature. From dielectric measurements of amorphous poly(ethylene terephthalate) heat-treated below T_g, it was found that the average relaxation time, the distribution of relaxation time and the dielectric strength increase with increase of heat treatment. From these results, it was concluded that the amorphous state becomes more random by heat treatment.     

油菜秸秆在碳酸乙烯酯中液化工艺的研究

利用碳酸乙烯酯(EC)为液化剂在常压条件下对油菜秸秆进行了液化试验。选择甲烷磺酸(MSA)作为最优催化剂,探讨了反应温度、反应时间、物料量、催化剂量4个因素对液化得率及黏度的影响。采用二次回归正交旋转组合设计对其液化工艺进行了优化。结果表明:最佳液化条件为反应温度165℃,反应时间70 min,物料量15.5%,催化剂量3.2%。在此条件下,液化得率可达到92.89%。     

多胺处理对鸭梨采后生理的影响

本文以鸭梨果实为原料,研究了精胺和亚精胺处理对果实呼吸强度、果实乙烯释放量、果肉硬度、果实可溶性固形物含量和果皮组织相对电导率变化的影响。试验结果表明,精胺和亚精胺处理对鸭梨果实的呼吸强度和乙烯释放量具有显著的抑制作用,贮藏240d时,多胺处理组果实可溶性固形物含量和果肉硬度显著高于对照组(p<0.01),果心褐变指数显著低于对照组(p<0.01)。     

预处理对增加红富士苹果细胞壁物质降解和出汁率的影响

为了通过简便易行的预处理增强果实细胞壁物质降解,提高苹果果实出汁率。文中测定了500mg/L乙烯利(E_1)和100mg/L乙烯利配合60℃热水(E_2)处理,对红富士果实堆放期细胞壁酶活性、细胞壁物质含量和出汁率的影响。结果表明:E_1使其果胶甲酯酶(PME)、纤维素酶(CS)活性高峰分别比对照提前6、3d,多聚半乳糖醛酸酶(PG)活性在前15d持续高于对照,木聚糖酶(Xyl)活性基本不变;处理12d后,果实细胞壁多糖中果胶类多糖、半纤维素类多糖和细胞壁残渣多糖含量分别下降到对照的80.1%、70.4%和75.7%;处理后9～18d,红富士苹果的出汁率较对照提高2.3%～4.0%;E_2抑制了果实PME活性,却普遍增强了0～6d内PG、Xyl、CS活性,亦促进了各类细胞壁物质的降解,0～9d内果实出汁率较对照高3.2%～7.1%。     

1-MCP对切分哈密瓜保鲜效果的研究

以新疆哈密瓜(8601)为材料,在5℃贮藏温度下,研究了1-MCP 对切分哈密瓜生理、品质和食用安全性的影响。结果表明：1.0μl/L 1-MCP 处理可显著抑制贮藏期间果实乙烯释放量,保持果实的感官,硬度、糖度和高VC 的含量,抑制切分哈密瓜透明化,降低了切分哈密瓜的细胞膜脂质过氧化水平,抑制微生物的数目,延长了切分哈密瓜的货架期。